Analysis of sagittal alignment changes in the spine-pelvis joint in sitting and standing positions after long- or short-segment fixation to the pelvis for lumbar degenerative diseases

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While preoperative changes in sagittal alignment are well studied, postoperative adaptations, particularly following spinal fixation extending to the pelvis, are less understood. Therefore, the present study aimed to examine sagittal changes in the spine, pelvis, and joints in sitting and standing positions after short- or long-segment posterior spinal fixation extending to the pelvis. Methods : This cross-sectional study analyzed patients who underwent long- or short-segment instrumented fusion to the pelvis for lumbar degenerative disease at our hospital from June 2018 to October 2019. Patients were grouped based on the number of internal fixation segments, both short and long. Sagittal parameters were measured in standing and sitting positions and matched for sex, gender, height, weight, and other related parameters. Statistical analysis was performed using t -tests and Mann–Whitney U tests. Results : A total of 98 patients were included, of whom 55 were included in the long-segmengroup (31 men, 24 women; mean age of 63.1 ± 8.5 years). In the long-segment group, no significant changes were observed between standing and sitting positions (P > 0.05). In the short-segment group, significant changes were observed in the sacral vertical axis, pelvic tilt, sacral slope, thoracic kyphosis, lumbar lordosis, T1 pelvic angle, T1 spinopelvic inclination, acetabular tilt, and pelvic-femoral angle between the two positions (P < 0.05). The difference in pelvic femoral angle changes between the groups was also significant (P < 0.05). Conclusions : In the short-segment group, transitioning from standing to sitting leads to greater sagittal changes, including decreased lumbar lordosis and forward trunk lean, with smaller hip joints than in the long-segment internal fixation group. spine pelvis lumbar degenerative disease sagittal alignment spinal fixation internal fixation postoperative adaptation Figures Figure 1 Figure 2 Figure 3 1. Introduction The spine, pelvis, and joints form an interconnected system, where these components coordinate, interact, and influence one another to maintain overall bodily balance. Lumbar degenerative diseases primarily include lumbar spinal stenosis, lumbar disc herniation, lumbar spondylolisthesis, and lumbar degenerative scoliosis. The main clinical symptoms of these conditions include low back pain, intermittent claudication, and motor and sensory impairments in both lower extremities caused by nerve involvement [ 1 ]. Lumbar degeneration in the older population often leads to a decreased lumbar lordosis (LL), posterior pelvic tilt (PT), and an increased acetabular anteversion angle [ 2 ]. This is particularly pronounced in older patients with low pelvic incidence (PI), whose pelvis exhibits limited compensatory reserve capacity [ 2 ]. Consequently, impingement of the posterior acetabular margin results in a “pseudo-flexion” posture of the knee joint and a forward shift of the center of gravity of the trunk, in accordance with the “principle of minimum energy expenditure” [ 2 ]. The pelvis, often described as the “pelvic vertebra,” connects the spine to the lower extremity joints. Under normal conditions, transitioning from standing to sitting positions involves a posterior PT, a reduction in LL, and a forward shift of the center of gravity of the trunk, allowing the body to achieve a new sagittal balance [ 3 ]. However, limited research has explored how the sagittal plane parameters of the spine, pelvis, and joints change and interact following posterior spinal fixation and fusion extending to the pelvis. The present study aimed to analyze sitting and standing radiographic data from patients with lumbar degenerative diseases treated with short- or long-segment posterior spinal fixation extending to the pelvis. By analyzing changes in sagittal plane parameters and their intrinsic relationships, this study provides spinal surgeons with a reference for designing personalized, holistic, and comprehensive surgical plans. 2. Materials and methods 2.1. Patient recruitment This cross-sectional study enrolled patients who underwent posterior lumbar or thoracolumbar fixation to the pelvis, with selective decompression and bone grafting fusion surgery for lumbar degenerative diseases, at the Chinese PLA General Hospital between June 2018 and October 2019. Inclusion criteria were as follows: 1) age ≥ 40 years; 2) posterior pedicle screw fixation surgery involving ≥ 2 vertebral segments, with the lowest instrumented vertebra (LIV) being the sacrum or ilium; 3) complete radiological and clinical data, including full-length anteroposterior and lateral spine radiographs in both sitting and standing positions obtained within 3 weeks postoperatively; and 4) diagnosis of lumbar degenerative diseases such as lumbar spinal stenosis, lumbar disc herniation, or degenerative lumbar scoliosis. The standard sitting position was defined as the body being naturally relaxed, with the hips and knees flexed at 90° and hands placed comfortably on the knees. Exclusion criteria were as follows: 1) history of thoracolumbar surgery or trauma; 2) ankylosing spondylitis, adult idiopathic scoliosis, Scheuermann’s disease, neuromuscular diseases, spinal tumors, or tuberculosis; 3) hip or knee joint diseases; and 4) prior lower limb surgery. This study was retrospective and, therefore, exempt from ethical review. 2.2. Measurement indicators of sagittal plane parameters of spinopelvic joints and clinical data collection 2.2.1. Imaging measurement indicators (Fig. 1) Sacral vertical axis (SVA): The distance from the C7 plumb line to the vertical line passing through the posterior superior corner of the sacrum. The balanced range for SVA in the sagittal plane is -5 cm to +5 cm. A positive value indicates that the C7 plumb line falls anterior to the posterior superior corner of the sacrum, whereas a negative value indicates it falls posterior to it. T1 spinopelvic inclination (T1SPI): A line is drawn from the centroid of T1 to the midpoint of the line connecting the two femoral heads. The angle between this line and a perpendicular line drawn from the midpoint of the line connecting the femoral heads defines the T1SPI. A positive value indicates that the T1 plumb line falls anterior to the midpoint, whereas a negative value indicates it falls posterior to it. T1 pelvic angle (TPA): This is the angle between two lines, one drawn from the centroid of T1 to the midpoint of the line connecting the two femoral heads and the other from the midpoint of the sacral endplate to the same midpoint. This geometric relationship is expressed as TPA = PT + T1SPI. Thoracic kyphosis (TK): The angle between the tangent to the upper endplate of T5 and the tangent to the lower endplate of T12. Thoracolumbar kyphosis (TLK): The angle between the tangent to the upper endplate of T11 and the tangent to the lower endplate of L1. Lumbar lordosis (LL): The angle between the tangent to the upper endplate of L1 and the tangent to the upper endplate of S1. PI: The angle between a line drawn from the midpoint of the sacral endplate to the midpoint of the line connecting the two femoral heads and a perpendicular line from the sacral endplate. PT: The angle between a line drawn from the midpoint of the sacral endplate to the midpoint of the line connecting the two femoral heads and a perpendicular line drawn from the same midpoint. Sacral slope (SS): The angle between the sacral endplate and the horizontal line. Acetabular tilt (AT): The angle between the line connecting the anterior and posterior edges of the acetabulum and the horizontal line in the sagittal plane. Sacro-acetabular angle (SA): The angle between the tangent to the sacral endplate and the line connecting the anterior and posterior edges of the acetabulum. This anatomical parameter reflects the inherent shape of the pelvis and is expressed geometrically as SA = SS + AT. Pelvicfemoral angle (PFA): The angle formed between a line connecting the midpoint of the sacral endplate to the center of the femoral head and a line parallel to the femoral shaft passing through the center of the femoral head. This parameter reflects the position of the femur relative to the pelvis. All parameters [4] were measured using Surgimap software (version 2.3; Surgimap, Methuen, MA, USA). Each parameter was measured three times consecutively by an attending spinal surgery physician, and the average value was recorded. 2.2.2. Clinical data collection Clinical data included patient age, sex, uppermost instrumented vertebra (UIV), PI-LL value, and global spinal alignment calculated as the sum of TK, LL, and PI [5]. 2.3. Patient grouping and variable matching The influence of the spine on the range of motion of the hip joint primarily stems from the vertebrae below L3 [6]. Therefore, the group with the UIV at or below L3 is defined as the short-segment internal fixation group, whereas the group with the UIV above L3 is classified as the long-segment internal fixation group. Based on a review of previous literature [7] ,factors that may influence changes in sagittal plane parameters in both sitting and standing positions were excluded. The variables matched in this study included age, sex, height, weight, and relevant standing parameters (PI-LL, TK + LL + PI, SVA, PI, PT, and SA) measured within 3 weeks postoperatively [7–9]. 2.4. Statistical analysis Statistical analysis was performed using SPSS software (version 23.0; SPSS Inc., San Diego, CA, USA). Paired sample t -tests were conducted to compare sagittal plane parameters of the spine and pelvic joints between sitting and standing positions. Independent sample t -tests were used for parameters that followed a normal distribution in both groups. For variables that did not follow a normal distribution, the Mann–Whitney U test was applied. Categorical variables were analyzed using the Pearson χ² test or Fisher’s exact test. A P-value < 0.05 was considered statistically significant. 3. Results 3.1. Patient characteristic and variable matching This study included 98 patients in total. The long-segment internal fixation group comprised 55 patients (31 men and 24 women) with an average age of 63.1 ± 8.5 years (range: 48–85 years), while the short-segment internal fixation included 43 patients in (22 men and 21 women) with an average age of 60.5 ± 7.2 years (range: 45–82 years). In the long-segment group, the UIV was fixed above T9 in 12 patients, between T9 and T11 in 32 patients, and between T12 and L2 in 11 patients. In the short-segment internal fixation group, the UIV was located at L5 in 23 patients, at L4 in 12 patients, and at L3 in 8 patients. The LIV for both groups was the sacrum or ilium. The results of the variable matching between the two groups are presented in Table 1 . There were no significant differences between the groups in terms of sex, age, height, weight, or postoperative standing sagittal plane parameters of the spine and pelvic joints, including PI, PT, SA, PI-LL, TK + LL + PI, and SVA (P > 0.05). The average number of instrumented segments was 10.2 ± 2.3 vertebrae in the long-segment group and 2.7 ± 0.8 vertebrae in the short-segment group, with a significant difference between the two groups (P < 0.05). Table 1 Propensity matching of patients with long-segment and short-segment fusion. Long-segment fusion Short-segment fusion P-value Age (years) 63.1 ± 8.5 60.5 ± 7.2 0.426 Sex (male: female) 31:24 22:21 0.608 Height (m) 1.65 ± 0.53 1.66 ± 0.64 0.486 Weight (Kg) 62.25 ± 7.80 64.32 ± 9.65 0.762 PI (°) 56.75 ± 9.47 58.35 ± 8.68 0.536 PT (°) 26.26 ± 10.28 24.71 ± 6.23 0.612 SA (°) 74.28 ± 12.56 72.45 ± 14.25 0.452 Standing PI-LL (°) 6.75 ± 15.28 7.23 ± 18.76 0.873 Standing TK + LL + PI (°) 45.47 ± 19.37 43.82 ± 20.32 0.315 Standing SVA (mm) 8.2 ± 25.8 6.8 ± 23.3 0.591 A P-value of < 0.05 was considered statistically significant. PI, Pelvic Incidence; PT, pelvic tilt; SA, sacral slope; LL, lumbar lordosis; TK, thoracic kyphosis; SVA, sagittal vertical axis 3.2. Comparison of sagittal plane parameters of the spine and pelvic joint in sitting and standing positions In the long-segment internal fixation group, the PFA significantly decreased by 85.91 ± 10.87° during the transition from standing to sitting positions (from 212.36 ± 23.87° to 126.45 ± 15.46°, respectively; P 0.05; Table 2 ). In the short-segment internal fixation group, transitioning from standing to sitting positions resulted in significant changes in several parameters. Specifically, the SVA increased by 14.8 ± 29.6 mm (from 6.8 ± 23.3 mm to 21.6 ± 21.2 mm), PT increased by 4.25 ± 7.56° (from 24.71 ± 6.23° to 28.96 ± 5.38°), SS decreased by 5.19 ± 9.61° (from 32.43 ± 9.26° to 27.24 ± 7.83°), TK increased by 5.84 ± 6.26° (from 24.78 ± 9.26° to 30.62 ± 10.46°), LL decreased by 15.15 ± 9.66° (from 56.72 ± 12.81° to 41.57 ± 13.47°), TPA increased by 8.13 ± 5.78° (from 19.33 ± 7.25° to 27.46 ± 8.68°), T1SPI increased by 5.07 ± 6.08° (from − 6.74 ± 5.36° to 1.67 ± 4.45°), AT increased by 5.42 ± 12.23° (from 37.94 ± 10.47° to 43.36 ± 12.56°), and PFA decreased by 75.63 ± 12.12° (from 216.37 ± 24.69° to 140.74 ± 17.54°, respectively). However, the PI, TLK, and SA exhibited no significant differences between the two positions (P > 0.05; Table 3 ). A comparison of the changes in PFA between the long-segment and short-segment internal fixation groups revealed a statistically significant difference, with values of 85.91 ± 10.87° vs. 75.63 ± 12.12°, respectively (P < 0.05). Representative cases from both groups are presented in Figs. 2 and 3 , respectively. Table 2 Comparisons of sagittal parameters of spine-pelvis-hip in patients with long-segment fusion. Standing position Sitting position P-value SVA (mm) 8.2 ± 25.8 6.26 ± 25.8 0.092 PI (°) 56.75 ± 9.47 - - PT (°) 26.26 ± 10.28 28.12 ± 9.11 0.716 SS (°) 29.55 ± 9.64 30.64 ± 7.63 0.532 TK (°) 32.86 ± 10.26 34.72 ± 9.76 0.571 LL (°) 52.46 ± 14.62 50.68 ± 11.24 0.642 TLK (°) 11.57 ± 5.36 12.43 ± 6.75 0.436 TPA (°) 20.86 ± 7.22 22.61 ± 6.31 0.096 T1SPI (°) -3.26 ± 6.42 -5.53 ± 5.21 0.0108 SA (°) 74.28 ± 12.56 - - AT (°) 41.53 ± 11.62 43.36 ± 10.82 0.513 PFA (°) 212.36 ± 23.87 126.45 ± 15.46 < 0.001 A P-value of < 0.05 was considered statistically significant. SVA, sagittal vertical axis; PI, pelvic incidence; PT, pelvic tilt; SS, sacral slope; TK, thoracic kyphosis; LL, lumbar lordosis; TLK, thoracolumbar kyphosis; TPA, thoracic pelvic angle; T1SPI, T1 slope pelvic incidence; SA, sacral angle; AT, axial tilt; PFA, pelvic femoral angle Table 3 Comparison of sagittal parameters of spine-pelvis-hip in patients with short-segment fusion. Standing position Sitting position P-value SVA (mm) 6.8 ± 23.3 21.6 ± 21.2 < 0.001 PI (°) 58.35 ± 8.68 - - PT (°) 24.71 ± 6.23 28.96 ± 5.38 < 0.05 SS (°) 32.43 ± 9.26 27.24 ± 7.83 < 0.05 TK (°) 24.78 ± 9.26 30.62 ± 10.46 < 0.001 LL (°) 56.72 ± 12.81 41.57 ± 13.47 < 0.001 TLK (°) 7.28 ± 3.54 7.95 ± 4.36 0.407 TPA (°) 19.33 ± 7.25 27.46 ± 8.68 < 0.001 T1SPI (°) -6.74 ± 5.36 -1.67 ± 4.45 < 0.05 SA (°) 72.45 ± 14.25 - - AT (°) 37.94 ± 10.47 43.36 ± 12.56 < 0.05 PFA (°) 216.37 ± 24.69 140.74 ± 17.54 < 0.001 A P-value of < 0.05 was considered statistically significant. SVA, sagittal vertical axis; PI, pelvic incidence; PT, pelvic tilt; SS, sacral slope; TK, thoracic kyphosis; LL, lumbar lordosis; TLK, thoracolumbar kyphosis; TPA, thoracic pelvic angle; T1SPI, T1 slope pelvic incidence; SA, sacral angle; AT, axial tilt; PFA, pelvic femoral angle 4. Discussion Owing to reduced mobility, the seated position plays a crucial role in the daily lives of older individuals. In recent years, research on changes in sagittal spinopelvic parameters during sitting has garnered significant attention. Notably, satisfaction with the seated position is a major factor influencing the quality of life for patients following spinal surgery [ 10 ]. However, most existing studies primarily examine preoperative changes in sagittal spinopelvic parameters in the seated position, with limited exploration of postoperative changes. In particular, there is a lack of data on how varying surgical segment lengths influence these parameters. Furthermore, the spinopelvic joint functions as an integrated and interconnected system. Spinal internal fixation and fusion surgeries can alter pelvic mobility, indirectly affecting joint activity. Conversely, joint activity can also influence the sagittal alignment of the spine [ 11 ]. These interactions highlight the need for further investigation into the complex relationships among the spine, pelvis, and joints. The present study included 98 patients who were categorized into long-segment and short-segment internal fixation groups based on the length of the fixed segments. To minimize the influence of unrelated factors on sagittal spinopelvic parameters, we matched these factors through a literature review and focused on analyzing the impact of fixation segment length on sagittal spinopelvic parameters in adults with degenerative lumbar diseases following surgery. In a study by Suzuki et al. [ 12 ], preoperative sagittal parameter measurements were conducted on 47 older patients (23 men, 24 women; mean age 75.3 ± 4.6 years) with degenerative lumbar diseases in the seated position. The authors reported that PT increased by 10.3 ± 7.4°, SS decreased by 9.2 ± 6.9°, while LL decreased by 8.5 ± 7.0° from the standing to the seated position. Bernstein et al. [ 13 ] conducted a retrospective study comparing full-length spine radiographs in flexion and extension positions for 100 patients without a history of spinal or hip surgery and 50 patients with varying degrees of lumbar fusion. They concluded that L5-S1 lumbar fusion had the greatest impact on pelvic mobility [ 14 , 15 ]. In our study, the long-segment internal fixation group exhibited no significant differences in PT, SS, and LL changes between the standing and seated positions. In contrast, in the short-segment internal fixation group, PT increased by 4.25 ± 7.56°, SS decreased by 5.19 ± 9.61°, and LL decreased by 15.15 ± 9.66° during the shift from the standing to the seated position. Our results indicated that in patients with short-segment internal fixation, the transition from standing to sitting is characterized by a forward trunk lean, a decrease in LL, and increases in SVA, TK, T1 pelvic angle, and T1 spinopelvic inclination angle. Their pelvis retains some capacity for backward rotation, resulting in an increased acetabular anteversion angle during the transition. We attribute these differences to the extent of spinal fixation. Specifically, in the long-segment internal fixation group, 80% of patients had the upper vertebrae fixed at T12 or above, with the fixation spanning the lumbar and sacral vertebrae. This extensive fixation restricted changes in LL and pelvic retroversion in the seated position. Pelvic retroversion is primarily characterized by an increase in PT, a decrease in SS, and a compensatory decrease in LL. Conversely, in the short-segment internal fixation group, the lumbar spine retained some flexibility in the seated position. Although fixation to the sacrum limited pelvic retroversion to some extent, the fixed segments completed the remaining retroversion compensation along with the pelvis as LL decreased. Therefore, the changes in SS and PT in the short-segment internal fixation group were smaller than the preoperative changes reported in the literature. In contrast, the long-segment internal fixation group exhibited minimal changes between the standing and seated positions. In a cross-sectional study by Zhou S et al. [ 16 ] involving 95 middle-aged and older volunteers (40 men, 55 women; mean age 53.3 ± 6.2 years), full-length spine radiographs taken in standing and seated positions revealed significant changes in sagittal parameters. They reported that SVA increased by 42.7 ± 27.4 mm, TPA increased by 9.2 ± 7.8°, and TK increased by 4.7 ± 5.2° when transitioning from standing to sitting. In our study, we observed no significant differences in SVA, TPA, TK, or T1SPI changes between the standing and seated positions in the long-segment internal fixation group. However, in the short-segment internal fixation group, SVA increased by 14.8 ± 29.6 mm, TPA increased by 8.13 ± 5.78°, TK increased by 5.84 ± 6.26°, and T1SPI increased by 5.07 ± 6.08° from standing to sitting. With long-segment spinal internal fixation, the thoracic and lumbar spine becomes rigid, preventing forward flexion in a relaxed seated position and resulting in minimal changes in these parameters. Although the long-segment group exhibited no statistically significant difference in SVA between positions, we noted that a subset of patients experienced slight trunk retroversion when seated. We attribute this phenomenon partly to sampling error and partly to anatomical factors. Specifically, patients with relatively high PI may have a smaller acetabular anteversion angle. During the transition from standing to sitting, these patients may experience an impingement pelvis between the proximal femur and the anterior acetabular rim due to insufficient pelvic retroversion and acetabular anteversion [ 17 – 19 ]. To compensate, the trunk retroverts as a whole, facilitating pelvic retroversion and increasing acetabular anteversion, thereby avoiding impingement of the anterior acetabular rim. We further measured changes in the sagittal pelvic and joint parameters between standing and seated positions in both groups. In the long-segment internal fixation group, AT exhibited no significant changes, whereas PFA decreased by 85.91 ± 10.87°. In the short-segment internal fixation group, AT increased by 5.42 ± 12.23°, and PFA decreased by 75.63 ± 12.12°. The difference in PFA changes between the two groups was statistically significant. The PFA reflects the relative position of the femur to the pelvis, with its variation indicating the degree of hip flexion relative to the pelvis [ 20 – 22 ]. In the long-segment internal fixation group, the inability of the pelvis to retrovert during the transition from standing to sitting prevents changes in acetabulum orientation, leading to minimal AT variation. The hip joint compensates with hyperflexion to achieve a relaxed, upright seated posture. Conversely, in the short-segment internal fixation group, the pelvis retains some retroversion capability, resulting in an increase in AT during the transition. While hip hyperflexion is also present in this group, the degree of PFA change is significantly smaller than that of the long-segment group. Based on these findings, we propose that reconstructing the sagittal alignment of the spinopelvic joint to improve its seated position adaptability is critical for certain patients, particularly those with high PI, hip joint diseases, or limited hip joint mobility. Achieving optimal spinopelvic alignment may help reduce postoperative complications such as proximal junctional kyphosis. This study had certain limitations. First, there may have been a sampling error, as potential variability, particularly in the trunk retroversion phenomenon, was observed in some patients in the long-segment group. Second, anatomical variations, such as PI and acetabular anteversion, may have influenced the results, introducing variability in the outcomes. Third, we may not have captured all patients who underwent posterior lumbar or thoracolumbar fixation to the pelvis, as selective decompression and bone grafting fusion surgery for lumbar degenerative diseases, especially within subgroups, could limit the generalizability of the findings. Finally, as this was a single-center study, the results may not be generalizable to other institutions. 5. Conclusions Our study demonstrated that the reduction of fixed segments allows the pelvis to retain some posterior rotation capability. As the number of fixed segments decreases, the range of motion of the patient's hip joint will also decrease, reducing the risk of hip dislocation and subsequent hip joint diseases. Therefore, we recommend that surgeons perform fixation on as few segments as necessary based on surgical requirements and adjust the curvature of the connecting rod to maintain appropriate sagittal alignment and minimize the impact on the spine-pelvis joint. Abbreviations AT, Axial tilt LL, Lumbar lordosis PFA, Pelvic femoral angle PI, Pelvic incidence PT, Pelvic tilt SA, Sacral angle SS, Sacral slope SVA, Sagittal vertical axis T1SPI, T1 slope pelvic incidence TK, Thoracic kyphosis TLK, Thoracolumbar kyphosis TPA, Thoracic pelvic angle Declarations Ethics approval and consent to participate The study is in accordance with the Declaration of Helsinki, and it is retrospective and exempt from ethical review, it should not mention ethics committee approval and written informed consent unless required by institutional policies. Consent for publication N/A. Availability of data and materials The data supporting this study’s findings are available from the first author (Yue Ma) upon request. Competing interests The authors declare no conflict of interest. Funding This work was supported by Beijing Nova Program (Grant 20230484464). The funder of the study had no role in study design, data collection, data analysis, data interpretation, or writing of the report. The corresponding author had full access to all the data in the study and had final responsibility for the decision to submit for publication. Author contributions YM: conceptualization, methodology, and writing – original draft preparation. CGW: formal analysis, validation, and visualization. HY: software, data curation, and investigation. GG and CX: data curation and supervision. CG: writing – review & editing, and resources. All authors contributed to the manuscript and approved the final version for submission. Acknowledgments We thank the Department of Orthopedics, Chinese PLA General Hospital, for their support during this study. References Bao T, Wang C, Wang Y, Wang T, Zhang Q, Gao F, et al. Relationship between paravertebral muscle degeneration and spinal-pelvic sagittal parameters in patients with lumbar disc herniation. 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Bone Joint J. 2017;99–B(Suppl A)(1 Supple A):37-45. https://doi.org/10.1302/0301-620X.99B1.BJJ-2016-0415.R1 Bo J, Zhao X, Hua Z, Li J, Qi X, Shen Y. Impact of sarcopenia and sagittal parameters on the residual back pain after percutaneous vertebroplasty in patients with osteoporotic vertebral compression fracture. J Orthop Surg Res. 2022;17:111. https://doi.org/10.1186/s13018-022-03009-4. Menge TJ, Truex NW. Femoroacetabular impingement: A common cause of hip pain. Phys Sportsmed. 2018;46:139-44. https://doi.org/10.1080/00913847.2018.1436844. Mills ES, Talehakimi A, Urness M, Wang J, Piple AS, Chung B, et al. Anteroposterior pelvic radiograph findings correlate with sagittal spinopelvic motion. Bone Joint J. 2023;105-B:496-503. https://doi.org/10.1302/0301-620X.105B5.BJJ-2022-0945.R1 Haffer H, Hu Z, Wang Z, Müllner M, Hardt S, Pumberger M. Association of age and spinopelvic function in patients receiving a total hip arthroplasty. Sci Rep. 2023;13:2589. https://doi.org/10.1038/s41598-023-29545-5 Heckmann N, Tezuka T, Bodner RJ, Dorr LD. Functional Anatomy of the Hip Joint. J Arthroplasty. 2021;36:374-8. https://doi.org/10.1016/j.arth.2020.07.065 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 30 Aug, 2025 Read the published version in Journal of Orthopaedic Surgery and Research → Version 1 posted Editorial decision: Revision requested 03 Jul, 2025 Reviews received at journal 20 Jun, 2025 Reviewers agreed at journal 19 Jun, 2025 Reviewers agreed at journal 18 Jun, 2025 Reviewers invited by journal 17 Jun, 2025 Editor assigned by journal 17 Jun, 2025 Submission checks completed at journal 17 Jun, 2025 First submitted to journal 15 Jun, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6899313","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":473646705,"identity":"b536021b-9f00-4666-b33a-4f8c10b4d5bc","order_by":0,"name":"Yue Ma","email":"","orcid":"","institution":"the First Medical Center of PLA General Hospital","correspondingAuthor":false,"prefix":"","firstName":"Yue","middleName":"","lastName":"Ma","suffix":""},{"id":473646706,"identity":"13078137-906c-436e-81d0-119235239cd6","order_by":1,"name":"ChunGuo Wang","email":"","orcid":"","institution":"the Fourth Medical Center of PLA General Hospital","correspondingAuthor":false,"prefix":"","firstName":"ChunGuo","middleName":"","lastName":"Wang","suffix":""},{"id":473646707,"identity":"5df7f188-8484-4861-97cf-b38bb4dc6662","order_by":2,"name":"Han Yu","email":"","orcid":"","institution":"the Fourth Medical Center of PLA General Hospital","correspondingAuthor":false,"prefix":"","firstName":"Han","middleName":"","lastName":"Yu","suffix":""},{"id":473646708,"identity":"038ed6d9-3c73-48dd-97e2-b2f859586f4d","order_by":3,"name":"Benzhang Tao","email":"","orcid":"","institution":"the First Medical Center of PLA General Hospital","correspondingAuthor":false,"prefix":"","firstName":"Benzhang","middleName":"","lastName":"Tao","suffix":""},{"id":473646711,"identity":"f4f6b7aa-c1e5-4167-a350-1b1e5858ed1c","order_by":4,"name":"Chao Gao","email":"","orcid":"","institution":"the Fourth Medical Center of PLA General Hospital","correspondingAuthor":false,"prefix":"","firstName":"Chao","middleName":"","lastName":"Gao","suffix":""},{"id":473646714,"identity":"53a60254-31fe-4ec7-85c5-734cbc07b7e6","order_by":5,"name":"Gan Gao","email":"","orcid":"","institution":"the First Medical Center of PLA General Hospital","correspondingAuthor":false,"prefix":"","firstName":"Gan","middleName":"","lastName":"Gao","suffix":""},{"id":473646716,"identity":"036fefc4-50cd-4c4f-80ea-66c02399f913","order_by":6,"name":"Chao Xue","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA40lEQVRIiWNgGAWjYDACZuYGCIO9seFAQoWEnDxhLYxALQlABs/hgw8+nLEwNmwgqAemRSIt2XBmW0UiwwECGnTbGRsf/vxhk8fPkGMmzTtPIoGxgfnhoxt4tJgdZmw25klIK5ZsOAPUsk0ij52Bzdg4B7+WNmmGhMOJGw72gLUUMzbwsEkT0NL+8wdQy/7DPEAtcyQSGw4Q1tLGwAOyhY0N6P0G4rQ0S/OkpSXOOMMMDORjEsaGzYT8cv7wwY8/bGwS++c/BEZlTZ2cPHvzw8f4tGABzKQpHwWjYBSMglGABQAABRxOqrVymUYAAAAASUVORK5CYII=","orcid":"","institution":"the Fourth Medical Center of PLA General Hospital","correspondingAuthor":true,"prefix":"","firstName":"Chao","middleName":"","lastName":"Xue","suffix":""}],"badges":[],"createdAt":"2025-06-15 16:08:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6899313/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6899313/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1186/s13018-025-06199-9","type":"published","date":"2025-08-30T15:58:07+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":85181870,"identity":"28e69322-3cb5-4961-98ce-798a52664345","added_by":"auto","created_at":"2025-06-23 07:27:09","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":142528,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSagittal parameters of the pelvis-hip\u003c/strong\u003e. (a and b) Changes in sagittal parameters of the pelvis-hip in the standing and sitting positions, respectively. Sacro-Acetabular angle (SA): The angle between the line tangent to the upper endplate of S1 and the line tangent to the anterior and posterior edges of the acetabulum. Acetabular tilt (AT): The angle between the horizontal line and the line tangent to the anterior and posterior edges of the acetabulum. Sacral slope (SS): The angle between the horizontal line and the line tangent to the upper endplate of S1. The geometrical relationship of complementary angles is expressed as SA = SS + AT. Pelvic femoral angle (PFA): The angle between the line from the center of the S1 endplate to the center of the femoral head and the line parallel to the femoral diaphysis.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6899313/v1/64ca0f37eccfd03cc93eb5f7.png"},{"id":85180841,"identity":"c50b7142-fdd8-4ec0-820a-7d7cbdebfeb8","added_by":"auto","created_at":"2025-06-23 07:19:09","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":411591,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eA representative patient.\u003c/strong\u003e A 69-year-old man underwent an elective posterior thoracolumbar instrumented fusion (T10-S1) and decompression for degenerative lumbar scoliosis. The sagittal parameters of the spine, pelvis, and hip were measured from a long cassette lateral radiograph in both standing and sitting positions. In the standing position, the measurements were as follows: SVA -20.84 mm, PI 53.42°, PT 26.95°, SS 26.47°, SA 70.50°, AT 43.25°, PFA 216.24°, TK 41.28°, TLK 13.82°, LL 52.79°, TPA 18.14°, and T1SPI -13.13°. In the sitting position, the measurements were as follows: SVA -26.19 mm, PI 54.33°, PT 28.36°, SS 25.97°, SA 70.78°, AT 46.32°, PFA 126.12°, TK 43.75°, TLK 14.91°, LL 53.46°, TPA 16.39°, and T1SPI -11.97°. SVA, sagittal vertical axis; PI, pelvic incidence; PT, pelvic tilt; SS, sacral slope; TK, thoracic kyphosis; LL, lumbar lordosis; TLK, thoracolumbar kyphosis; TPA, thoracic pelvic angle; T1SPI, T1 slope pelvic incidence; SA, sacral angle; AT, axial tilt; PFA, pelvic femoral angle.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6899313/v1/6af05af6036523c473717dae.png"},{"id":85183331,"identity":"8cab1bfe-caec-4ad0-96cc-11bfb2083f48","added_by":"auto","created_at":"2025-06-23 07:43:09","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":353015,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eA representative patient.\u003c/strong\u003e A 65-year-old woman underwent L4–S1 posterior lumbar interbody fusion for lumbar spinal stenosis. The sagittal parameters of the spine, pelvis, and hip were measured from a long cassette lateral radiograph in both standing and sitting positions. In the standing position, the measurements were as follows: SVA -12.50 mm, PI 66.42°, PT 25.54°, SS 40.88°, SA 68.64°, AT 27.66°, PFA 212.12°, TK 18.83°, TLK 8.83°, LL 62.37°, TPA 15.40°, and T1SPI -10.14°. In the sitting position, the measurements were as follows: SVA 10.45 mm, PI 67.33°, PT 30.36°, SS 36.97°, SA 69.78°, AT 32.81°, PFA 128.6°, TK 24.10°, TLK 9.23°, LL 48.84°, TPA 22.56°, and T1SPI -7.80°. SVA, sagittal vertical axis; PI, pelvic incidence; PT, pelvic tilt; SS, sacral slope; TK, thoracic kyphosis; LL, lumbar lordosis; TLK, thoracolumbar kyphosis; TPA, thoracic pelvic angle; T1SPI, T1 slope pelvic incidence; SA, sacral angle; AT, axial tilt; PFA, pelvic femoral angle.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6899313/v1/fe8f8864142cf052bb5e771d.png"},{"id":90345630,"identity":"725ebfb2-a4a4-4f8c-978d-db217222e9e9","added_by":"auto","created_at":"2025-09-01 16:10:43","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2071129,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6899313/v1/4316b50d-564c-462c-847e-df0f49fbeb80.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Analysis of sagittal alignment changes in the spine-pelvis joint in sitting and standing positions after long- or short-segment fixation to the pelvis for lumbar degenerative diseases","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe spine, pelvis, and joints form an interconnected system, where these components coordinate, interact, and influence one another to maintain overall bodily balance. Lumbar degenerative diseases primarily include lumbar spinal stenosis, lumbar disc herniation, lumbar spondylolisthesis, and lumbar degenerative scoliosis. The main clinical symptoms of these conditions include low back pain, intermittent claudication, and motor and sensory impairments in both lower extremities caused by nerve involvement [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. Lumbar degeneration in the older population often leads to a decreased lumbar lordosis (LL), posterior pelvic tilt (PT), and an increased acetabular anteversion angle [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. This is particularly pronounced in older patients with low pelvic incidence (PI), whose pelvis exhibits limited compensatory reserve capacity [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Consequently, impingement of the posterior acetabular margin results in a \u0026ldquo;pseudo-flexion\u0026rdquo; posture of the knee joint and a forward shift of the center of gravity of the trunk, in accordance with the \u0026ldquo;principle of minimum energy expenditure\u0026rdquo; [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe pelvis, often described as the \u0026ldquo;pelvic vertebra,\u0026rdquo; connects the spine to the lower extremity joints. Under normal conditions, transitioning from standing to sitting positions involves a posterior PT, a reduction in LL, and a forward shift of the center of gravity of the trunk, allowing the body to achieve a new sagittal balance [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. However, limited research has explored how the sagittal plane parameters of the spine, pelvis, and joints change and interact following posterior spinal fixation and fusion extending to the pelvis.\u003c/p\u003e \u003cp\u003eThe present study aimed to analyze sitting and standing radiographic data from patients with lumbar degenerative diseases treated with short- or long-segment posterior spinal fixation extending to the pelvis. By analyzing changes in sagittal plane parameters and their intrinsic relationships, this study provides spinal surgeons with a reference for designing personalized, holistic, and comprehensive surgical plans.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cdiv\u003e\n \u003ch2\u003e2.1. Patient recruitment\u003c/h2\u003e\n \u003cp\u003eThis cross-sectional study enrolled patients who underwent posterior lumbar or thoracolumbar fixation to the pelvis, with selective decompression and bone grafting fusion surgery for lumbar degenerative diseases, at the Chinese PLA General Hospital between June 2018 and October 2019.\u003c/p\u003e\n \u003cp\u003eInclusion criteria were as follows: 1) age\u0026thinsp;\u0026ge;\u0026thinsp;40 years; 2) posterior pedicle screw fixation surgery involving\u0026thinsp;\u0026ge;\u0026thinsp;2 vertebral segments, with the lowest instrumented vertebra (LIV) being the sacrum or ilium; 3) complete radiological and clinical data, including full-length anteroposterior and lateral spine radiographs in both sitting and standing positions obtained within 3 weeks postoperatively; and 4) diagnosis of lumbar degenerative diseases such as lumbar spinal stenosis, lumbar disc herniation, or degenerative lumbar scoliosis. The standard sitting position was defined as the body being naturally relaxed, with the hips and knees flexed at 90\u0026deg; and hands placed comfortably on the knees.\u003c/p\u003e\n \u003cp\u003eExclusion criteria were as follows: 1) history of thoracolumbar surgery or trauma; 2) ankylosing spondylitis, adult idiopathic scoliosis, Scheuermann\u0026rsquo;s disease, neuromuscular diseases, spinal tumors, or tuberculosis; 3) hip or knee joint diseases; and 4) prior lower limb surgery. This study was retrospective and, therefore, exempt from ethical review.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv\u003e\n \u003ch2\u003e2.2. Measurement indicators of sagittal plane parameters of spinopelvic joints and clinical data collection\u003c/h2\u003e\n \u003cdiv\u003e\n \u003ch2\u003e2.2.1. Imaging measurement indicators (Fig. 1)\u003c/h2\u003e\n \u003col\u003e\n \u003cli\u003eSacral vertical axis (SVA): The distance from the C7 plumb line to the vertical line passing through the posterior superior corner of the sacrum. The balanced range for SVA in the sagittal plane is -5 cm to +5 cm. A positive value indicates that the C7 plumb line falls anterior to the posterior superior corner of the sacrum, whereas a negative value indicates it falls posterior to it.\u003c/li\u003e\n \u003cli\u003eT1 spinopelvic inclination (T1SPI): A line is drawn from the centroid of T1 to the midpoint of the line connecting the two femoral heads. The angle between this line and a perpendicular line drawn from the midpoint of the line connecting the femoral heads defines the T1SPI. A positive value indicates that the T1 plumb line falls anterior to the midpoint, whereas a negative value indicates it falls posterior to it.\u003c/li\u003e\n \u003cli\u003eT1 pelvic angle (TPA): This is the angle between two lines, one drawn from the centroid of T1 to the midpoint of the line connecting the two femoral heads and the other from the midpoint of the sacral endplate to the same midpoint. This geometric relationship is expressed as TPA = PT + T1SPI.\u003c/li\u003e\n \u003cli\u003eThoracic kyphosis (TK): The angle between the tangent to the upper endplate of T5 and the tangent to the lower endplate of T12.\u003c/li\u003e\n \u003cli\u003eThoracolumbar kyphosis (TLK): The angle between the tangent to the upper endplate of T11 and the tangent to the lower endplate of L1.\u003c/li\u003e\n \u003cli\u003eLumbar lordosis (LL): The angle between the tangent to the upper endplate of L1 and the tangent to the upper endplate of S1.\u003c/li\u003e\n \u003cli\u003ePI: The angle between a line drawn from the midpoint of the sacral endplate to the midpoint of the line connecting the two femoral heads and a perpendicular line from the sacral endplate.\u003c/li\u003e\n \u003cli\u003ePT: The angle between a line drawn from the midpoint of the sacral endplate to the midpoint of the line connecting the two femoral heads and a perpendicular line drawn from the same midpoint.\u003c/li\u003e\n \u003cli\u003eSacral slope (SS): The angle between the sacral endplate and the horizontal line.\u003c/li\u003e\n \u003cli\u003eAcetabular tilt (AT): The angle between the line connecting the anterior and posterior edges of the acetabulum and the horizontal line in the sagittal plane.\u003c/li\u003e\n \u003cli\u003eSacro-acetabular angle (SA): The angle between the tangent to the sacral endplate and the line connecting the anterior and posterior edges of the acetabulum. This anatomical parameter reflects the inherent shape of the pelvis and is expressed geometrically as SA = SS + AT.\u0026nbsp;\u003c/li\u003e\n \u003cli\u003ePelvicfemoral angle (PFA): The angle formed between a line connecting the midpoint of the sacral endplate to the center of the femoral head and a line parallel to the femoral shaft passing through the center of the femoral head. This parameter reflects the position of the femur relative to the pelvis.\u0026nbsp;\u003c/li\u003e\n \u003c/ol\u003e\n \u003cp\u003eAll parameters [4] were measured using Surgimap software (version 2.3; Surgimap, Methuen, MA, USA). Each parameter was measured three times consecutively by an attending spinal surgery physician, and the average value was recorded.\u0026nbsp;\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv\u003e\n \u003ch2\u003e2.2.2. Clinical data collection\u003c/h2\u003e\n \u003cp\u003eClinical data included patient age, sex, uppermost instrumented vertebra (UIV), PI-LL value, and global spinal alignment calculated as the sum of TK, LL, and PI [5].\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv\u003e\n \u003ch2\u003e2.3. Patient grouping and variable matching\u003c/h2\u003e\n \u003cp\u003eThe influence of the spine on the range of motion of the hip joint primarily stems from the vertebrae below L3 [6]. Therefore, the group with the UIV at or below L3 is defined as the short-segment internal fixation group, whereas the group with the UIV above L3 is classified as the long-segment internal fixation group. Based on a review of previous literature [7] ,factors that may influence changes in sagittal plane parameters in both sitting and standing positions were excluded. The variables matched in this study included age, sex, height, weight, and relevant standing parameters (PI-LL, TK\u0026thinsp;+\u0026thinsp;LL\u0026thinsp;+\u0026thinsp;PI, SVA, PI, PT, and SA) measured within 3 weeks postoperatively [7\u0026ndash;9].\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv\u003e\n \u003ch2\u003e2.4. Statistical analysis\u003c/h2\u003e\n \u003cp\u003eStatistical analysis was performed using SPSS software (version 23.0; SPSS Inc., San Diego, CA, USA). Paired sample \u003cem\u003et\u003c/em\u003e-tests were conducted to compare sagittal plane parameters of the spine and pelvic joints between sitting and standing positions. Independent sample \u003cem\u003et\u003c/em\u003e-tests were used for parameters that followed a normal distribution in both groups. For variables that did not follow a normal distribution, the Mann\u0026ndash;Whitney U test was applied. Categorical variables were analyzed using the Pearson \u0026chi;\u0026sup2; test or Fisher\u0026rsquo;s exact test. A P-value\u0026thinsp;\u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"3. Results","content":"\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1. Patient characteristic and variable matching\u003c/h2\u003e\n \u003cp\u003eThis study included 98 patients in total. The long-segment internal fixation group comprised 55 patients (31 men and 24 women) with an average age of 63.1\u0026thinsp;\u0026plusmn;\u0026thinsp;8.5 years (range: 48\u0026ndash;85 years), while the short-segment internal fixation included 43 patients in (22 men and 21 women) with an average age of 60.5\u0026thinsp;\u0026plusmn;\u0026thinsp;7.2 years (range: 45\u0026ndash;82 years). In the long-segment group, the UIV was fixed above T9 in 12 patients, between T9 and T11 in 32 patients, and between T12 and L2 in 11 patients. In the short-segment internal fixation group, the UIV was located at L5 in 23 patients, at L4 in 12 patients, and at L3 in 8 patients. The LIV for both groups was the sacrum or ilium.\u003c/p\u003e\n \u003cp\u003eThe results of the variable matching between the two groups are presented in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. There were no significant differences between the groups in terms of sex, age, height, weight, or postoperative standing sagittal plane parameters of the spine and pelvic joints, including PI, PT, SA, PI-LL, TK\u0026thinsp;+\u0026thinsp;LL\u0026thinsp;+\u0026thinsp;PI, and SVA (P\u0026thinsp;\u0026gt;\u0026thinsp;0.05). The average number of instrumented segments was 10.2\u0026thinsp;\u0026plusmn;\u0026thinsp;2.3 vertebrae in the long-segment group and 2.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8 vertebrae in the short-segment group, with a significant difference between the two groups (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003ePropensity matching of patients with long-segment and short-segment fusion.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eLong-segment fusion\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eShort-segment fusion\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eP-value\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAge (years)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e63.1\u0026thinsp;\u0026plusmn;\u0026thinsp;8.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e60.5\u0026thinsp;\u0026plusmn;\u0026thinsp;7.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.426\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSex (male: female)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e31:24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e22:21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.608\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eHeight (m)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.65\u0026thinsp;\u0026plusmn;\u0026thinsp;0.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.66\u0026thinsp;\u0026plusmn;\u0026thinsp;0.64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.486\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eWeight (Kg)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e62.25\u0026thinsp;\u0026plusmn;\u0026thinsp;7.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e64.32\u0026thinsp;\u0026plusmn;\u0026thinsp;9.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.762\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePI (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e56.75\u0026thinsp;\u0026plusmn;\u0026thinsp;9.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e58.35\u0026thinsp;\u0026plusmn;\u0026thinsp;8.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.536\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePT (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e26.26\u0026thinsp;\u0026plusmn;\u0026thinsp;10.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e24.71\u0026thinsp;\u0026plusmn;\u0026thinsp;6.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.612\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSA (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e74.28\u0026thinsp;\u0026plusmn;\u0026thinsp;12.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e72.45\u0026thinsp;\u0026plusmn;\u0026thinsp;14.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.452\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStanding PI-LL (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.75\u0026thinsp;\u0026plusmn;\u0026thinsp;15.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.23\u0026thinsp;\u0026plusmn;\u0026thinsp;18.76\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.873\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStanding TK\u0026thinsp;+\u0026thinsp;LL\u0026thinsp;+\u0026thinsp;PI (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e45.47\u0026thinsp;\u0026plusmn;\u0026thinsp;19.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e43.82\u0026thinsp;\u0026plusmn;\u0026thinsp;20.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.315\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStanding SVA (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.2\u0026thinsp;\u0026plusmn;\u0026thinsp;25.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.8\u0026thinsp;\u0026plusmn;\u0026thinsp;23.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.591\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"4\"\u003e\n \u003cp\u003eA P-value of \u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/p\u003e\n \u003cp\u003ePI, Pelvic Incidence; PT, pelvic tilt; SA, sacral slope; LL, lumbar lordosis; TK, thoracic kyphosis; SVA, sagittal vertical axis\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003ch2\u003e\u003cstrong\u003e3.2. Comparison of sagittal plane parameters of the spine and pelvic joint in sitting and standing positions\u003c/strong\u003e\u003c/h2\u003e\n \u003cp\u003eIn the long-segment internal fixation group, the PFA significantly decreased by 85.91\u0026thinsp;\u0026plusmn;\u0026thinsp;10.87\u0026deg; during the transition from standing to sitting positions (from 212.36\u0026thinsp;\u0026plusmn;\u0026thinsp;23.87\u0026deg; to 126.45\u0026thinsp;\u0026plusmn;\u0026thinsp;15.46\u0026deg;, respectively; P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Other sagittal plane parameters, including SVA, PI, PT, SS, TK, LL, TLK, TPA, T1SPI, SA, and AT, exhibited no statistically significant differences (P\u0026thinsp;\u0026gt;\u0026thinsp;0.05; Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eIn the short-segment internal fixation group, transitioning from standing to sitting positions resulted in significant changes in several parameters. Specifically, the SVA increased by 14.8\u0026thinsp;\u0026plusmn;\u0026thinsp;29.6 mm (from 6.8\u0026thinsp;\u0026plusmn;\u0026thinsp;23.3 mm to 21.6\u0026thinsp;\u0026plusmn;\u0026thinsp;21.2 mm), PT increased by 4.25\u0026thinsp;\u0026plusmn;\u0026thinsp;7.56\u0026deg; (from 24.71\u0026thinsp;\u0026plusmn;\u0026thinsp;6.23\u0026deg; to 28.96\u0026thinsp;\u0026plusmn;\u0026thinsp;5.38\u0026deg;), SS decreased by 5.19\u0026thinsp;\u0026plusmn;\u0026thinsp;9.61\u0026deg; (from 32.43\u0026thinsp;\u0026plusmn;\u0026thinsp;9.26\u0026deg; to 27.24\u0026thinsp;\u0026plusmn;\u0026thinsp;7.83\u0026deg;), TK increased by 5.84\u0026thinsp;\u0026plusmn;\u0026thinsp;6.26\u0026deg; (from 24.78\u0026thinsp;\u0026plusmn;\u0026thinsp;9.26\u0026deg; to 30.62\u0026thinsp;\u0026plusmn;\u0026thinsp;10.46\u0026deg;), LL decreased by 15.15\u0026thinsp;\u0026plusmn;\u0026thinsp;9.66\u0026deg; (from 56.72\u0026thinsp;\u0026plusmn;\u0026thinsp;12.81\u0026deg; to 41.57\u0026thinsp;\u0026plusmn;\u0026thinsp;13.47\u0026deg;), TPA increased by 8.13\u0026thinsp;\u0026plusmn;\u0026thinsp;5.78\u0026deg; (from 19.33\u0026thinsp;\u0026plusmn;\u0026thinsp;7.25\u0026deg; to 27.46\u0026thinsp;\u0026plusmn;\u0026thinsp;8.68\u0026deg;), T1SPI increased by 5.07\u0026thinsp;\u0026plusmn;\u0026thinsp;6.08\u0026deg; (from \u0026minus;\u0026thinsp;6.74\u0026thinsp;\u0026plusmn;\u0026thinsp;5.36\u0026deg; to 1.67\u0026thinsp;\u0026plusmn;\u0026thinsp;4.45\u0026deg;), AT increased by 5.42\u0026thinsp;\u0026plusmn;\u0026thinsp;12.23\u0026deg; (from 37.94\u0026thinsp;\u0026plusmn;\u0026thinsp;10.47\u0026deg; to 43.36\u0026thinsp;\u0026plusmn;\u0026thinsp;12.56\u0026deg;), and PFA decreased by 75.63\u0026thinsp;\u0026plusmn;\u0026thinsp;12.12\u0026deg; (from 216.37\u0026thinsp;\u0026plusmn;\u0026thinsp;24.69\u0026deg; to 140.74\u0026thinsp;\u0026plusmn;\u0026thinsp;17.54\u0026deg;, respectively). However, the PI, TLK, and SA exhibited no significant differences between the two positions (P\u0026thinsp;\u0026gt;\u0026thinsp;0.05; Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eA comparison of the changes in PFA between the long-segment and short-segment internal fixation groups revealed a statistically significant difference, with values of 85.91\u0026thinsp;\u0026plusmn;\u0026thinsp;10.87\u0026deg; vs. 75.63\u0026thinsp;\u0026plusmn;\u0026thinsp;12.12\u0026deg;, respectively (P\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Representative cases from both groups are presented in Figs. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e and \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e, respectively.\u003c/p\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eComparisons of sagittal parameters of spine-pelvis-hip in patients with long-segment fusion.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eStanding position\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSitting position\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eP-value\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSVA (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.2\u0026thinsp;\u0026plusmn;\u0026thinsp;25.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.26\u0026thinsp;\u0026plusmn;\u0026thinsp;25.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.092\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePI (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e56.75\u0026thinsp;\u0026plusmn;\u0026thinsp;9.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePT (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e26.26\u0026thinsp;\u0026plusmn;\u0026thinsp;10.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e28.12\u0026thinsp;\u0026plusmn;\u0026thinsp;9.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.716\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSS (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e29.55\u0026thinsp;\u0026plusmn;\u0026thinsp;9.64\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e30.64\u0026thinsp;\u0026plusmn;\u0026thinsp;7.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.532\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTK (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e32.86\u0026thinsp;\u0026plusmn;\u0026thinsp;10.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e34.72\u0026thinsp;\u0026plusmn;\u0026thinsp;9.76\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.571\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLL (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e52.46\u0026thinsp;\u0026plusmn;\u0026thinsp;14.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e50.68\u0026thinsp;\u0026plusmn;\u0026thinsp;11.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.642\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTLK (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e11.57\u0026thinsp;\u0026plusmn;\u0026thinsp;5.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e12.43\u0026thinsp;\u0026plusmn;\u0026thinsp;6.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.436\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTPA (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e20.86\u0026thinsp;\u0026plusmn;\u0026thinsp;7.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e22.61\u0026thinsp;\u0026plusmn;\u0026thinsp;6.31\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.096\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT1SPI (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-3.26\u0026thinsp;\u0026plusmn;\u0026thinsp;6.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-5.53\u0026thinsp;\u0026plusmn;\u0026thinsp;5.21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.0108\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSA (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e74.28\u0026thinsp;\u0026plusmn;\u0026thinsp;12.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAT (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e41.53\u0026thinsp;\u0026plusmn;\u0026thinsp;11.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e43.36\u0026thinsp;\u0026plusmn;\u0026thinsp;10.82\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.513\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePFA (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e212.36\u0026thinsp;\u0026plusmn;\u0026thinsp;23.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e126.45\u0026thinsp;\u0026plusmn;\u0026thinsp;15.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"4\"\u003e\n \u003cp\u003eA P-value of \u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/p\u003e\n \u003cp\u003eSVA, sagittal vertical axis; PI, pelvic incidence; PT, pelvic tilt; SS, sacral slope; TK, thoracic kyphosis; LL, lumbar lordosis; TLK, thoracolumbar kyphosis; TPA, thoracic pelvic angle; T1SPI, T1 slope pelvic incidence; SA, sacral angle; AT, axial tilt; PFA, pelvic femoral angle\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n \u003ctable id=\"Tab3\" border=\"1\" class=\"fr-table-selection-hover\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eComparison of sagittal parameters of spine-pelvis-hip in patients with short-segment fusion.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eStanding position\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSitting position\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eP-value\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSVA (mm)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e6.8\u0026thinsp;\u0026plusmn;\u0026thinsp;23.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e21.6\u0026thinsp;\u0026plusmn;\u0026thinsp;21.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePI (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e58.35\u0026thinsp;\u0026plusmn;\u0026thinsp;8.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePT (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e24.71\u0026thinsp;\u0026plusmn;\u0026thinsp;6.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e28.96\u0026thinsp;\u0026plusmn;\u0026thinsp;5.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSS (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e32.43\u0026thinsp;\u0026plusmn;\u0026thinsp;9.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e27.24\u0026thinsp;\u0026plusmn;\u0026thinsp;7.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTK (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e24.78\u0026thinsp;\u0026plusmn;\u0026thinsp;9.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e30.62\u0026thinsp;\u0026plusmn;\u0026thinsp;10.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLL (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e56.72\u0026thinsp;\u0026plusmn;\u0026thinsp;12.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e41.57\u0026thinsp;\u0026plusmn;\u0026thinsp;13.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTLK (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.28\u0026thinsp;\u0026plusmn;\u0026thinsp;3.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.95\u0026thinsp;\u0026plusmn;\u0026thinsp;4.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.407\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTPA (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e19.33\u0026thinsp;\u0026plusmn;\u0026thinsp;7.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e27.46\u0026thinsp;\u0026plusmn;\u0026thinsp;8.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eT1SPI (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-6.74\u0026thinsp;\u0026plusmn;\u0026thinsp;5.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-1.67\u0026thinsp;\u0026plusmn;\u0026thinsp;4.45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSA (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e72.45\u0026thinsp;\u0026plusmn;\u0026thinsp;14.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAT (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e37.94\u0026thinsp;\u0026plusmn;\u0026thinsp;10.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e43.36\u0026thinsp;\u0026plusmn;\u0026thinsp;12.56\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePFA (\u0026deg;)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e216.37\u0026thinsp;\u0026plusmn;\u0026thinsp;24.69\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e140.74\u0026thinsp;\u0026plusmn;\u0026thinsp;17.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\" colspan=\"4\"\u003e\n \u003cp\u003eA P-value of \u0026lt;\u0026thinsp;0.05 was considered statistically significant.\u003c/p\u003e\n \u003cp\u003eSVA, sagittal vertical axis; PI, pelvic incidence; PT, pelvic tilt; SS, sacral slope; TK, thoracic kyphosis; LL, lumbar lordosis; TLK, thoracolumbar kyphosis; TPA, thoracic pelvic angle; T1SPI, T1 slope pelvic incidence; SA, sacral angle; AT, axial tilt; PFA, pelvic femoral angle\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003cp\u003e\u003cbr\u003e\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4. Discussion","content":"\u003cp\u003eOwing to reduced mobility, the seated position plays a crucial role in the daily lives of older individuals. In recent years, research on changes in sagittal spinopelvic parameters during sitting has garnered significant attention. Notably, satisfaction with the seated position is a major factor influencing the quality of life for patients following spinal surgery [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. However, most existing studies primarily examine preoperative changes in sagittal spinopelvic parameters in the seated position, with limited exploration of postoperative changes. In particular, there is a lack of data on how varying surgical segment lengths influence these parameters. Furthermore, the spinopelvic joint functions as an integrated and interconnected system. Spinal internal fixation and fusion surgeries can alter pelvic mobility, indirectly affecting joint activity. Conversely, joint activity can also influence the sagittal alignment of the spine [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. These interactions highlight the need for further investigation into the complex relationships among the spine, pelvis, and joints. The present study included 98 patients who were categorized into long-segment and short-segment internal fixation groups based on the length of the fixed segments. To minimize the influence of unrelated factors on sagittal spinopelvic parameters, we matched these factors through a literature review and focused on analyzing the impact of fixation segment length on sagittal spinopelvic parameters in adults with degenerative lumbar diseases following surgery.\u003c/p\u003e \u003cp\u003eIn a study by Suzuki et al. [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e], preoperative sagittal parameter measurements were conducted on 47 older patients (23 men, 24 women; mean age 75.3\u0026thinsp;\u0026plusmn;\u0026thinsp;4.6 years) with degenerative lumbar diseases in the seated position. The authors reported that PT increased by 10.3\u0026thinsp;\u0026plusmn;\u0026thinsp;7.4\u0026deg;, SS decreased by 9.2\u0026thinsp;\u0026plusmn;\u0026thinsp;6.9\u0026deg;, while LL decreased by 8.5\u0026thinsp;\u0026plusmn;\u0026thinsp;7.0\u0026deg; from the standing to the seated position. Bernstein et al. [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e] conducted a retrospective study comparing full-length spine radiographs in flexion and extension positions for 100 patients without a history of spinal or hip surgery and 50 patients with varying degrees of lumbar fusion. They concluded that L5-S1 lumbar fusion had the greatest impact on pelvic mobility [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. In our study, the long-segment internal fixation group exhibited no significant differences in PT, SS, and LL changes between the standing and seated positions. In contrast, in the short-segment internal fixation group, PT increased by 4.25\u0026thinsp;\u0026plusmn;\u0026thinsp;7.56\u0026deg;, SS decreased by 5.19\u0026thinsp;\u0026plusmn;\u0026thinsp;9.61\u0026deg;, and LL decreased by 15.15\u0026thinsp;\u0026plusmn;\u0026thinsp;9.66\u0026deg; during the shift from the standing to the seated position. Our results indicated that in patients with short-segment internal fixation, the transition from standing to sitting is characterized by a forward trunk lean, a decrease in LL, and increases in SVA, TK, T1 pelvic angle, and T1 spinopelvic inclination angle. Their pelvis retains some capacity for backward rotation, resulting in an increased acetabular anteversion angle during the transition. We attribute these differences to the extent of spinal fixation. Specifically, in the long-segment internal fixation group, 80% of patients had the upper vertebrae fixed at T12 or above, with the fixation spanning the lumbar and sacral vertebrae. This extensive fixation restricted changes in LL and pelvic retroversion in the seated position. Pelvic retroversion is primarily characterized by an increase in PT, a decrease in SS, and a compensatory decrease in LL. Conversely, in the short-segment internal fixation group, the lumbar spine retained some flexibility in the seated position. Although fixation to the sacrum limited pelvic retroversion to some extent, the fixed segments completed the remaining retroversion compensation along with the pelvis as LL decreased. Therefore, the changes in SS and PT in the short-segment internal fixation group were smaller than the preoperative changes reported in the literature. In contrast, the long-segment internal fixation group exhibited minimal changes between the standing and seated positions.\u003c/p\u003e \u003cp\u003eIn a cross-sectional study by Zhou S et al. [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e] involving 95 middle-aged and older volunteers (40 men, 55 women; mean age 53.3\u0026thinsp;\u0026plusmn;\u0026thinsp;6.2 years), full-length spine radiographs taken in standing and seated positions revealed significant changes in sagittal parameters. They reported that SVA increased by 42.7\u0026thinsp;\u0026plusmn;\u0026thinsp;27.4 mm, TPA increased by 9.2\u0026thinsp;\u0026plusmn;\u0026thinsp;7.8\u0026deg;, and TK increased by 4.7\u0026thinsp;\u0026plusmn;\u0026thinsp;5.2\u0026deg; when transitioning from standing to sitting. In our study, we observed no significant differences in SVA, TPA, TK, or T1SPI changes between the standing and seated positions in the long-segment internal fixation group. However, in the short-segment internal fixation group, SVA increased by 14.8\u0026thinsp;\u0026plusmn;\u0026thinsp;29.6 mm, TPA increased by 8.13\u0026thinsp;\u0026plusmn;\u0026thinsp;5.78\u0026deg;, TK increased by 5.84\u0026thinsp;\u0026plusmn;\u0026thinsp;6.26\u0026deg;, and T1SPI increased by 5.07\u0026thinsp;\u0026plusmn;\u0026thinsp;6.08\u0026deg; from standing to sitting. With long-segment spinal internal fixation, the thoracic and lumbar spine becomes rigid, preventing forward flexion in a relaxed seated position and resulting in minimal changes in these parameters. Although the long-segment group exhibited no statistically significant difference in SVA between positions, we noted that a subset of patients experienced slight trunk retroversion when seated. We attribute this phenomenon partly to sampling error and partly to anatomical factors. Specifically, patients with relatively high PI may have a smaller acetabular anteversion angle. During the transition from standing to sitting, these patients may experience an impingement pelvis between the proximal femur and the anterior acetabular rim due to insufficient pelvic retroversion and acetabular anteversion [\u003cspan additionalcitationids=\"CR18\" citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. To compensate, the trunk retroverts as a whole, facilitating pelvic retroversion and increasing acetabular anteversion, thereby avoiding impingement of the anterior acetabular rim.\u003c/p\u003e \u003cp\u003eWe further measured changes in the sagittal pelvic and joint parameters between standing and seated positions in both groups. In the long-segment internal fixation group, AT exhibited no significant changes, whereas PFA decreased by 85.91\u0026thinsp;\u0026plusmn;\u0026thinsp;10.87\u0026deg;. In the short-segment internal fixation group, AT increased by 5.42\u0026thinsp;\u0026plusmn;\u0026thinsp;12.23\u0026deg;, and PFA decreased by 75.63\u0026thinsp;\u0026plusmn;\u0026thinsp;12.12\u0026deg;. The difference in PFA changes between the two groups was statistically significant. The PFA reflects the relative position of the femur to the pelvis, with its variation indicating the degree of hip flexion relative to the pelvis [\u003cspan additionalcitationids=\"CR21\" citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. In the long-segment internal fixation group, the inability of the pelvis to retrovert during the transition from standing to sitting prevents changes in acetabulum orientation, leading to minimal AT variation. The hip joint compensates with hyperflexion to achieve a relaxed, upright seated posture. Conversely, in the short-segment internal fixation group, the pelvis retains some retroversion capability, resulting in an increase in AT during the transition. While hip hyperflexion is also present in this group, the degree of PFA change is significantly smaller than that of the long-segment group. Based on these findings, we propose that reconstructing the sagittal alignment of the spinopelvic joint to improve its seated position adaptability is critical for certain patients, particularly those with high PI, hip joint diseases, or limited hip joint mobility. Achieving optimal spinopelvic alignment may help reduce postoperative complications such as proximal junctional kyphosis.\u003c/p\u003e \u003cp\u003eThis study had certain limitations. First, there may have been a sampling error, as potential variability, particularly in the trunk retroversion phenomenon, was observed in some patients in the long-segment group. Second, anatomical variations, such as PI and acetabular anteversion, may have influenced the results, introducing variability in the outcomes. Third, we may not have captured all patients who underwent posterior lumbar or thoracolumbar fixation to the pelvis, as selective decompression and bone grafting fusion surgery for lumbar degenerative diseases, especially within subgroups, could limit the generalizability of the findings. Finally, as this was a single-center study, the results may not be generalizable to other institutions.\u003c/p\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003eOur study demonstrated that the reduction of fixed segments allows the pelvis to retain some posterior rotation capability. As the number of fixed segments decreases, the range of motion of the patient's hip joint will also decrease, reducing the risk of hip dislocation and subsequent hip joint diseases. Therefore, we recommend that surgeons perform fixation on as few segments as necessary based on surgical requirements and adjust the curvature of the connecting rod to maintain appropriate sagittal alignment and minimize the impact on the spine-pelvis joint.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cp\u003eAT, Axial tilt\u003c/p\u003e\n\u003cp\u003eLL, Lumbar lordosis\u003c/p\u003e\n\u003cp\u003ePFA, Pelvic femoral angle\u003c/p\u003e\n\u003cp\u003ePI, Pelvic incidence\u003c/p\u003e\n\u003cp\u003ePT, Pelvic tilt\u003c/p\u003e\n\u003cp\u003eSA, Sacral angle\u003c/p\u003e\n\u003cp\u003eSS, Sacral slope\u003c/p\u003e\n\u003cp\u003eSVA, Sagittal vertical axis\u003c/p\u003e\n\u003cp\u003eT1SPI, T1 slope pelvic incidence\u003c/p\u003e\n\u003cp\u003eTK, Thoracic kyphosis\u003c/p\u003e\n\u003cp\u003eTLK, Thoracolumbar kyphosis\u003c/p\u003e\n\u003cp\u003eTPA, Thoracic pelvic angle\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eEthics approval and consent to participate\u003c/h2\u003e\n\u003cp\u003eThe study is in accordance with the Declaration of Helsinki, and it is retrospective and exempt from ethical review, it should not mention ethics committee approval and written informed consent unless required by institutional policies.\u003c/p\u003e\n\u003ch2\u003eConsent for publication\u003c/h2\u003e\n\u003cp\u003eN/A.\u003c/p\u003e\n\u003ch2\u003eAvailability of data and materials\u003c/h2\u003e\n\u003cp\u003eThe data supporting this study\u0026rsquo;s findings are available from the first \u0026nbsp;author (Yue Ma) upon request.\u003c/p\u003e\n\u003ch2\u003eCompeting interests\u003c/h2\u003e\n\u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e\n\u003ch2\u003eFunding\u0026nbsp;\u003c/h2\u003e\n\u003cp\u003eThis work was supported by Beijing Nova Program (Grant 20230484464). The funder of the study had no role in study design, data collection, data analysis, data interpretation, or writing of the report. The corresponding author had full access to all the data in the study and had final responsibility for the decision to submit for publication.\u003c/p\u003e\n\u003ch2\u003eAuthor contributions\u003c/h2\u003e\n\u003cp\u003eYM: conceptualization, methodology, and writing \u0026ndash; original draft preparation.\u0026nbsp;CGW: formal analysis, validation, and visualization. HY: software, data curation, and investigation. GG and CX: data curation and supervision. CG: writing \u0026ndash; review \u0026amp; editing, and resources. All authors contributed to the manuscript and approved the final version for submission.\u003c/p\u003e\n\u003ch2\u003eAcknowledgments\u003c/h2\u003e\n\u003cp\u003eWe thank the Department of Orthopedics, Chinese PLA General Hospital, for their support during this study. \u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBao T, Wang C, Wang Y, Wang T, Zhang Q, Gao F, et al. Relationship between paravertebral muscle degeneration and spinal-pelvic sagittal parameters in patients with lumbar disc herniation. Sci Rep. 2024;14:192. https://doi.org/10.1038/s41598-023-50836-4.\u003c/li\u003e\n\u003cli\u003eLazennec JY, Brusson A, Rousseau MA. Hip-spine relations and sagittal balance clinical consequences. Eur Spine J. 2011;20(Suppl 5):686-98. https://doi.org/10.1007/s00586-011-1937-9. \u003c/li\u003e\n\u003cli\u003eMullin JP, Asghar J, Patel AI, Osorio JA, Smith JS, Ames CP, et al. Changes in alignment at untreated vertebral levels following short-segment fusion using personalized interbody cages: Leveraging personalized medicine to reduce the risk of reoperation. Int J Spine Surg. 2024;18(Suppl 1):S32-40. https://doi.org/10.14444/8639.\u003c/li\u003e\n\u003cli\u003eVallesi V, Shetty G, Moll M, Zweers P, Berger M, Christiaanse E, et al. Development and validation of a practical solution for detecting motion artefacts in the EOS X-ray system. Sci Rep. 2024;14:4837. https://doi.org/10.1038/s41598-024-55373-2. \u003c/li\u003e\n\u003cli\u003eSangondimath G, Mallepally AR, Marathe N, Salimath S, Chhabra HS. Radiographic analysis of the sagittal alignment of spine and pelvis in asymptomatic Indian population. Asian Spine J. 2022;16:107-18. https://doi.org/10.31616/asj.2020.0301. \u003c/li\u003e\n\u003cli\u003eIke H, Dorr LD, Trasolini N, Stefl M, McKnight B, Heckmann N. Spine-pelvis-hip relationship in the functioning of a total hip replacement. J Bone Joint Surg Am. 2018;100:1606-15. https://doi.org/10.2106/JBJS.17.00403.\u003c/li\u003e\n\u003cli\u003eRoberts SB, Tsirikos AI. Paediatric spinal deformity surgery: Complications and their management. Healthcare (Basel, Switzerland). 2022;10:2519. https://doi.org/10.3390/healthcare10122519. \u003c/li\u003e\n\u003cli\u003eTachibana T, Fujii M, Kitamura K, Nakamura T, Nakashima Y. Does acetabular coverage vary between the supine and standing positions in patients with hip dysplasia? Clin Orthop Relat Res. 2019;477:2455-66. https://doi.org/10.1097/CORR.0000000000000898.\u003c/li\u003e\n\u003cli\u003eMerrill RK, Kim JS, Leven DM, Kim JH, Cho SK. Beyond pelvic incidence-lumbar lordosis mismatch: The importance of assessing the entire spine to achieve global sagittal alignment. Glob Spine J. 2017;7:536-42. https://doi.org/10.1177/2192568217699405. \u003c/li\u003e\n\u003cli\u003eDharnipragada R, Bostrom N, Bertogliat M, Denduluri LS, Dhawan S, Ladd B, et al. Sagittal balance in sitting and standing positions: A systematic review of radiographic measures. Heliyon. 2024;10:e28545. https://doi.org/10.1016/j.heliyon.2024.e28545.\u003c/li\u003e\n\u003cli\u003eMasquefa T, Verdier N, Gille O, Boissi\u0026egrave;re L, Obeid I, Maillot C, et al. Change in acetabular version after lumbar pedicle subtraction osteotomy to correct postoperative flat back: EOS\u0026reg; measurements of 38 acetabula. Orthop Traumatol Surg Res. 2015;101:655-9. https://doi.org/10.1016/j.otsr.2015.07.013.\u003c/li\u003e\n\u003cli\u003eSuzuki H, Endo K, Mizuochi J, Murata K, Nishimura H, Matsuoka Y, et al. Sagittal lumbo-pelvic alignment in the sitting position of elderly persons. J Orthop Sci. 2016;21:713-7. https://doi.org/10.1016/j.jos.2016.06.015.\u003c/li\u003e\n\u003cli\u003eBernstein J, Charette R, Sloan M, Lee GC. Spinal fusion is associated with changes in acetabular orientation and reductions in pelvic mobility. Clin Orthop Relat Res. 2019;477:324-30. https://doi.org/10.1097/CORR.0000000000000390. \u003c/li\u003e\n\u003cli\u003eEbrahimkhani M, Arjmand N, Shirazi-Adl A. Adjacent segments biomechanics following lumbar fusion surgery: a musculoskeletal finite element model study. Eur Spine J. 2022;31:1630-9. https://doi.org/10.1007/s00586-022-07262-3\u003c/li\u003e\n\u003cli\u003eFan W, Zhang C, Wang QD, Guo LX, Zhang M. The effects of topping-off instrumentation on biomechanics of sacroiliac joint after lumbosacral fusion. Comput Biol Med. 2023;164:107357. https://doi.org/10.1016/j.compbiomed.2023.107357 \u003c/li\u003e\n\u003cli\u003eZhou S, Sun Z, Li W, Wang W, Su T, Du C, et al. The standing and sitting sagittal spinopelvic alignment of Chinese young and elderly population: does age influence the differences between the two positions?. Eur Spine J. 2020;29:405-12. https://doi.org/10.1007/s00586-019-06185-w.\u003c/li\u003e\n\u003cli\u003eStefl M, Lundergan W, Heckmann N, McKnight B, Ike H, Murgai R, et al. Spinopelvic mobility and acetabular component position for total hip arthroplasty. Bone Joint J. 2017;99\u0026ndash;B(Suppl A)(1 Supple A):37-45. https://doi.org/10.1302/0301-620X.99B1.BJJ-2016-0415.R1\u003c/li\u003e\n\u003cli\u003eBo J, Zhao X, Hua Z, Li J, Qi X, Shen Y. Impact of sarcopenia and sagittal parameters on the residual back pain after percutaneous vertebroplasty in patients with osteoporotic vertebral compression fracture. J Orthop Surg Res. 2022;17:111. https://doi.org/10.1186/s13018-022-03009-4. \u003c/li\u003e\n\u003cli\u003eMenge TJ, Truex NW. Femoroacetabular impingement: A common cause of hip pain. Phys Sportsmed. 2018;46:139-44. https://doi.org/10.1080/00913847.2018.1436844. \u003c/li\u003e\n\u003cli\u003eMills ES, Talehakimi A, Urness M, Wang J, Piple AS, Chung B, et al. Anteroposterior pelvic radiograph findings correlate with sagittal spinopelvic motion. Bone Joint J. 2023;105-B:496-503. https://doi.org/10.1302/0301-620X.105B5.BJJ-2022-0945.R1\u003c/li\u003e\n\u003cli\u003eHaffer H, Hu Z, Wang Z, M\u0026uuml;llner M, Hardt S, Pumberger M. Association of age and spinopelvic function in patients receiving a total hip arthroplasty. Sci Rep. 2023;13:2589. https://doi.org/10.1038/s41598-023-29545-5\u003c/li\u003e\n\u003cli\u003eHeckmann N, Tezuka T, Bodner RJ, Dorr LD. Functional Anatomy of the Hip Joint. J Arthroplasty. 2021;36:374-8. https://doi.org/10.1016/j.arth.2020.07.065\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"journal-of-orthopaedic-surgery-and-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"josr","sideBox":"Learn more about [Journal of Orthopaedic Surgery and Research](http://josr-online.biomedcentral.com)","snPcode":"13018","submissionUrl":"https://submission.nature.com/new-submission/13018/3","title":"Journal of Orthopaedic Surgery and Research","twitterHandle":"@MSKmedBMC","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"spine, pelvis, lumbar degenerative disease, sagittal alignment, spinal fixation, internal fixation, postoperative adaptation","lastPublishedDoi":"10.21203/rs.3.rs-6899313/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6899313/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eBackground:\u003c/strong\u003e The spine, pelvis, and joints maintain sagittal balance, which is often disrupted in lumbar degenerative diseases. While preoperative changes in sagittal alignment are well studied, postoperative adaptations, particularly following spinal fixation extending to the pelvis, are less understood. Therefore, the present study aimed to examine sagittal changes in the spine, pelvis, and joints in sitting and standing positions after short- or long-segment posterior spinal fixation extending to the pelvis.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods\u003c/strong\u003e: This cross-sectional study analyzed patients who underwent long- or short-segment instrumented fusion to the pelvis for lumbar degenerative disease at our hospital from June 2018 to October 2019. Patients were grouped based on the number of internal fixation segments, both short and long. Sagittal parameters were measured in standing and sitting positions and matched for sex, gender, height, weight, and other related parameters. Statistical analysis was performed using\u003cem\u003e t\u003c/em\u003e-tests and Mann–Whitney U tests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults\u003c/strong\u003e: A total of 98 patients were included, of whom 55 were included in the long-segmengroup (31 men, 24 women; mean age of 63.1 ± 8.5 years). In the long-segment group, no significant changes were observed between standing and sitting positions (P \u0026gt; 0.05). In the short-segment group, significant changes were observed in the sacral vertical axis, pelvic tilt, sacral slope, thoracic kyphosis, lumbar lordosis, T1 pelvic angle, T1 spinopelvic inclination, acetabular tilt, and pelvic-femoral angle between the two positions (P \u0026lt; 0.05). The difference in pelvic femoral angle changes between the groups was also significant (P \u0026lt; 0.05).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusions\u003c/strong\u003e: In the short-segment group, transitioning from standing to sitting leads to greater sagittal changes, including decreased lumbar lordosis and forward trunk lean, with smaller hip joints than in the long-segment internal fixation group.\u003c/p\u003e","manuscriptTitle":"Analysis of sagittal alignment changes in the spine-pelvis joint in sitting and standing positions after long- or short-segment fixation to the pelvis for lumbar degenerative diseases","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-23 07:19:05","doi":"10.21203/rs.3.rs-6899313/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-07-03T23:32:21+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-21T00:59:14+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"49777789144081702550174135681712614761","date":"2025-06-19T13:26:45+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"55673497196982051092076727802347674748","date":"2025-06-18T06:59:29+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-06-18T00:58:26+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-06-17T10:05:06+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-06-17T07:21:59+00:00","index":"","fulltext":""},{"type":"submitted","content":"Journal of Orthopaedic Surgery and Research","date":"2025-06-15T16:02:30+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"journal-of-orthopaedic-surgery-and-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"josr","sideBox":"Learn more about [Journal of Orthopaedic Surgery and Research](http://josr-online.biomedcentral.com)","snPcode":"13018","submissionUrl":"https://submission.nature.com/new-submission/13018/3","title":"Journal of Orthopaedic Surgery and Research","twitterHandle":"@MSKmedBMC","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"76329365-6143-4d20-b4b5-395b1facfb1d","owner":[],"postedDate":"June 23rd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-09-01T16:10:00+00:00","versionOfRecord":{"articleIdentity":"rs-6899313","link":"https://doi.org/10.1186/s13018-025-06199-9","journal":{"identity":"journal-of-orthopaedic-surgery-and-research","isVorOnly":false,"title":"Journal of Orthopaedic Surgery and Research"},"publishedOn":"2025-08-30 15:58:07","publishedOnDateReadable":"August 30th, 2025"},"versionCreatedAt":"2025-06-23 07:19:05","video":"","vorDoi":"10.1186/s13018-025-06199-9","vorDoiUrl":"https://doi.org/10.1186/s13018-025-06199-9","workflowStages":[]},"version":"v1","identity":"rs-6899313","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6899313","identity":"rs-6899313","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}