Hounsfield unit is associated with vertebral body re-collapse 3 months after surgery in working-age patients with a thoracolumbar burst fracture: A retrospective register-based cohort study

Hounsfield unit is associated with vertebral body re-collapse 3 months after surgery in working-age patients with a thoracolumbar burst fracture: A retrospective register-based cohort study | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Hounsfield unit is associated with vertebral body re-collapse 3 months after surgery in working-age patients with a thoracolumbar burst fracture: A retrospective register-based cohort study Jabbar Mohammed, Ryo Fujita, Johan Wänman, Mikael Kontakis, Fabian Burmeister, and 5 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6376244/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Purpose Factors associated with early re-collapse after posterior fixation of thoracolumbar burst fractures have been sparsely examined in previous studies. We investigated the factors associated with re-collapse within the first 3 months after posterior fixation of thoracolumbar burst fractures. Methods This retrospective study used data from the Swedish Fracture Register (2015–2019), encompassing patients aged 18 to 66 who sustained a single-level thoracolumbar burst fracture between T11 and L3 and underwent posterior fixation. The fractures were classified by a modified AO classification and the load sharing classification (LSC). Hounsfield unit (HU) values were used to evaluate bone quality. Vertebral collapse assessment included measurements of the kyphosis angle, wedge angle, and anterior/posterior height. Moreover, pull-out of pedicle screws was assessed. Multiple logistic regression analysis assessed the factors associated with re-collapse within 3 months after surgery Results This study comprised 100 participants, of whom 58 were male and 42 were female. Some 16 patients had radiographic vertebral re-collapse and 15 had pedicle screw pull-out. A statistically significant association was observed between HU values and re-collapse (odds ratio [OR]: 0.97, 95% confidence interval [CI]: 0.94–0.99). Preoperative LSC also tended to be associated with re-collapse (OR: 2.35, 95% CI: 1.07–6.82). However, no association with screw insertion depth or the number of fixated vertebrae was seen in this study. Conclusion Three months post-surgery, a statistically significant association was noted between HU values and early re-collapse after posterior spinal fixation in patients with thoracolumbar burst fractures. Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction Burst fractures are compression fractures of the vertebral body, characterized by damage to the posterior vertebral wall and at least one of the end plates[ 1 ]. They most commonly occur at the thoracolumbar junction, where the biomechanical forces are highest[ 2 ]. Burst fractures account for almost 10–20% of all thoracolumbar fractures and are most common in young males with high-energy trauma[ 3 ]. Burst fractures often lead to prolonged disability, chronic pain, and extended sick leave[ 4 ]. Posterior instrumented fusion is the most commonly used approach for thoracolumbar burst fractures[ 5 ]. Some surgeons, however, recommend anterior fusion for cases scoring ≥ 7 on the load sharing classification (LSC) [ 6 , 7 ]. In recent years, the posterior approach alone has shown good outcomes and faster return-to-work than the combined anterior-posterior approach, which is particularly advantageous for working-age individuals[ 8 ]. One important complication of posterior approaches is the early postoperative re-collapse of a well-reduced vertebral body, which is associated with correction loss, posttraumatic kyphosis, implant failure, and revision surgery[ 9 ]. Various strategies have been explored to prevent implant failure in posterior approaches, including vertebroplasty[ 10 ], calcium hydroxyapatite augmentation[ 11 ], and screw insertion into the fractured vertebral body[ 12 , 13 ]. Few studies have investigated factors associated with vertebral re-collapse after surgery for burst fractures. It has previously been reported that age at the time of surgery and preoperative body height loss were associated with re-collapse following posterior instrumented fusion for thoracolumbar burst fractures[ 9 ]. This study investigates factors associated with early postoperative (3 months) collapse of thoracolumbar burst fractures in working-age (18–66) people. Materials and methods Study population This retrospective study included data from patients registered in the Swedish Fracture Register (SFR) between 2015 and 2019. The SFR is a nationwide quality register covering all fracture types in Sweden, with spinal fractures incorporated since 2015, classified by a modified AO Spine system for standardized data collection[ 14 , 15 ]. Patients of working age with a single-level thoracolumbar burst fracture between T10 and L3 treated with posterior fixation were included. Patients with co-existing fractures in the same level pedicles or adjacent posterior structures (lamina, transverse, or spinous processes) were eligible if the posterior tension band was patent or indeterminate. Exclusion criteria included neurological injury beyond a single-level root (spinal cord or cauda equina injury), low-energy trauma, and pathological fractures. Comorbidity variables (diabetes, heart disease, osteoporosis) and reoperations within 1 year were collected from the Swedish National Patient Register, maintained by the National Board of Health and Welfare[ 16 ]. This was done by linking patient records using their unique social security numbers, allowing the register to identify relevant comorbidities based on ICD-10 codes recorded during any inpatient hospital stay or specialized outpatient visit. Medical image analysis Medical images were collected from the treating hospitals’ radiological departments. Patients underwent computed tomography (CT) and/or magnetic resonance imaging (MRI) within 2 weeks of the injury, followed by CT immediately after surgery and X-ray or CT 3 months after surgery. CT and MRI scans were acquired in the supine position, while X-rays were taken in the lateral decubitus position. Thoracolumbar CT was performed using Siemens Somatom Definition Flash (Siemens AG, Germany) and Canon Aquilion Prime (Canon Medical Systems, Japan) in helical mode with 120 kVp, adaptive tube load, and a slice thickness of 0.6–0.7 mm. Multiplanar reconstructions were generated in three orientations (1.0–3.0 mm thickness). Images were stored and analyzed using the institutional PACS. The evaluation of Kyphosis and vertebral body height assessments were conducted following the methodology outlined by Tang et al.[ 17 ]. Measurements included (1) kyphosis angle (Cobb angle between the superior endplate of the upper vertebra and the inferior endplate of the lower vertebra), (2) wedge angle (angle between the superior and inferior endplates of the fractured vertebra), and (3) the ratio of anterior to posterior vertebral body height (Fig. 4 ). These parameters were assessed preoperatively, immediately postoperatively, and at 3 months postoperatively. Re-collapse was defined as an anterior height loss of at least 20%[ 9 ]. The adjusted anterior height was calculated using the height ratio of adjacent vertebrae on immediate postoperative and 3-month postoperative images. Bone quality was assessed using Hounsfield unit (HU) values from the L1 vertebral body, measured on preoperative 3D CT using an oval region of interest within the trabecular bone of the middle axial slice (Fig. 5). If L1 were fractured, L2 was used instead[ 18 ]. The depth of pedicle screws within the vertebral body (% depth) was measured postoperatively based on previous described methods by Fujita et al.[ 19 ]. Measurements were taken bilaterally from the most cranial and caudal vertebrae within the fixation segment, and the mean % depth was calculated. To minimize potential observer errors, two independent orthopedic surgeons (SB and FB) not involved in the treatment of the study patients evaluated digital radiographs magnified twice. Intraclass correlation coefficients were assessed for kyphosis, wedge angles, body height, and HU values. The number of patients with screws inserted in the fractured vertebra was also evaluated. By using preoperative CT, the fracture was classified according to the LSC and a modified version of the 2013 AO spine injury classification system[ 14 ]. Patients were divided into two groups based on their LSC score: 68 patients had an LSC score ≥ 7 and patients had an LSC score < 7. The progression of the kyphosis angle, wedge angle, and A/P height ratio was then compared between the two groups. The measurement of pull-out of pedicle screw from the vertebral body Pull-out measurements of the pedicle screws were assessed by comparing immediate postoperative and 3-month postoperative images. The most cranial and caudal screws at fixation levels were examined. For cases with CT scans at both time points, pull-out was defined as ≥ 2 mm displacement on axial images, based on previous criteria[ 20 ]. When only lateral X-rays were available 3 months post-surgery, pull-out was evaluated against sagittal images from the immediate postoperative CT. Two orthopedic spine surgeons (JM and RF) independently conducted the assessment. Surgery All patients underwent posterior instrumented stabilization with either an open or minimally invasive approach. Given the extant evidence, a pedicle screw should be inserted at least one level above and below the fracture vertebra[ 5 ]. All surgeries were performed by either a consultant orthopedic surgeon or a neurosurgeon specializing in spine surgery. The surgical procedure was performed within 2 weeks of the injury date. Statistics analysis A Shapiro-Wilk test was conducted to assess distributional characteristics. Normally distributed data were expressed as mean with standard deviation (SD) and non-normally distributed data as median with interquartile range (IQR). Mann-Whitney U tests were used to assess group differences for continuous variables; Fisher's exact test was computed for the comparison of proportions. Paired t-tests assessed differences in kyphosis angle, wedge angle, and A/P vertebral height ratio between preoperative and immediate postoperative measurements and between immediate postoperative and 3-month postoperative measurements. Multiple logistic regression analysis was performed to identify factors associated with re-collapse. A backward-forward stepwise regression was used, selecting variable combinations that minimized the Akaike information criterion. Inclusion criteria were based on univariate analyses, considering variables significant (p < 0.05) or approaching significance (p < 0.2). Statistical analyses were performed using SPSS for Mac (version 29.0; IBM Corp., Armonk, NY, USA). Ethics, funding, and potential conflict of interest The study adhered to the Helsinki Declaration's ethical principles and was approved by the Swedish Ethical Review Authority (Approval No: 2021-00011). Results The patient selection process for this study is illustrated in Fig. 1 . A cohort of 100 patients with burst fractures was included. Their demographic characteristics are summarized in Table 1. Screws placed in the most cranial fixed vertebra tended to be inserted deeper into the vertebral body than those in the most caudal fixed vertebra. Based on the modified AO classification, the most common fracture type was A4-B0, accounting for 56% of cases, and L1 was the most frequent level for the fractures, accounting for 51% of cases. The median load sharing classification (LSC) score was 8, exceeding the threshold of 7, where anterior column reconstruction is generally recommended. Of the 100 patients, three underwent additional surgery within 1 year: one due to surgical site infection, one due to neurological deficits, and one due to implant failure. Postoperative vertebral collapse The data on the corrections angle achieved by the surgery, the progression of kyphosis, wedge angles, and the anterior/posterior height ratio (A/P ratio) of vertebra collapse are shown in Table 2. The immediate postoperative measurements revealed a reduction in the average kyphosis angle and wedge angle compared to their preoperative values, with the means decreasing from 10.7 to -2.3° and from 14.7 to 5.9°, respectively (p < 0.0001 for both). However, vertebral collapse had progressed by the 3-month follow-up, leading to increases in both angles. At this later time point, the mean kyphosis angle had risen to 2.9° and the mean wedge angle to 10.3°. The progression of the angles over this period averaged 5.7° for kyphosis and 4.4° for the wedge angle (ps < 0.0001 for both). The A/P ratios demonstrated a similar progression. While surgery effectively improved the vertebral A/P ratio, a slight collapse was observed during the 3-month follow-up. The average A/P ratio increased from 0.68 to 0.87 units postoperatively but decreased to 0.76 units at the 3-month follow-up, reflecting a progression of 0.1 (both ps < 0.0001). Evaluation of screw pull-out In this study, 95 cases were analyzed for screw pull-out after excluding five cases: two cases were excluded due to severe rotation observed on postoperative radiographs, which rendered evaluation impossible; one case involved rod breakage; one case had a dislodged set screw; and one case had a pedicle screw placed entirely outside the pedicle. These exclusions were implemented to ensure the reliability of the analysis. Of the 95 patients evaluated, 15 (15%) had screw pull-out within 3 months of surgery. Eight patients (8%) had pull-out in only the cranial screw, one (1%) in only the caudal screw, and six (6%) in both. Comparisons between patients with and without re-collapse Sixteen patients had radiographic vertebral re-collapse 3 months after surgery. Compared to the non-re-collapse group, the re-collapse group had a significantly higher proportion of females (56.3% vs. 43,7.1%, p = 0.02) and lower HU values (160 vs. 197.5, p = 0.02). Additionally, the re-collapse group showed significantly greater progression in KA (11.8 vs. 4.5, p < 0.001), WA (10.4 vs. 3.3, p < 0.001), and A/P vertebral height loss (0.23 vs. 0.08, p < 0.001) compared to the non-re-collapse group (Table 3). Multiple logistic regression analysis of potential factors associated with re-collapse A multiple logistic regression analysis was conducted to examine the association between potential factors and the re-collapse of the fractured vertebra 3 months after surgery. A statistically significant association was observed between HU value and re-collapse (odds ratio [OR]: 0.97; 95% confidence interval [CI]: 0.94–0.99). Preoperative LSC also showed a tendency to be associated with re-collapse (OR: 2.35, 95% CI: 1.07–6.82, p = 0.06). No statistically significant association with screw insertion depth or the number of fixed vertebrae was observed (Table 4). Comparison of vertebral collapse at 3 months postoperatively between LSC ≥ 7 and LSC < 7 We compared the progression of the kyphosis angle, wedge angle, and A/P height ratio between patients with LSC scores ≥ 7 and LSC scores < 7. Sixteen patients had LSC scores < 7 and 68 had LSC scores ≥ 7. There was a significant difference in wedge angle and A/P height ratio between the two groups (both ps = 0.04), while there was no statistically significant difference in kyphosis angle (p = 0.5) (Table 5). Discussion Our major finding demonstrated a significant association between lower HU values and early re-collapse following posterior spinal fixation in patients with thoracolumbar burst fractures, including those of working age. Meanwhile, screw insertion depth and the number of fixation levels were not associated with early re-collapse. Kohno et al. reported a 29% re-collapse rate among patients aged 60–86. The authors concluded that although posterior fixation yielded favorable clinical outcomes, the high incidence of postoperative complications due to bone fragility persisted[ 21 ]. Our study examined working-age adults, of whom only three were diagnosed with osteoporosis. A recent report defined normal lumbar HU values as ≥ 170 and osteoporotic values as ≤ 115. The average L1 HU in this study was 190, indicating a relatively healthy population[ 22 ]. Despite this, a statistically significant association persisted between HU values and re-collapse, suggesting that a larger-scale study is warranted to establish a re-collapse HU threshold independent of osteoporosis. Additionally, it indicates the importance of postoperative bone quality assessment even in this age group. Preoperative LSC tended to be associated with re-collapse. The LSC was originally developed to predict screw breakage or indicate the need for anterior reconstruction; its development was based on older-generation Steffe plates and screws, without considering soft tissue damage[ 7 ]. Subsequent research has shown that posterior instrumentation alone may suffice, even in cases with high LSC scores, with no clear correlation between LSC and instrumentation failure or correction loss[ 7 ]. Patients with an LSC score of ≥ 7 had significantly greater progression of wedge angle and A/P height ratio than those with an LSC score of < 7. However, there was no difference in the progression of the kyphosis angle. This observation suggests that, despite severe burst fractures with high LSC scores, posterior reconstruction alone may lead to vertebral re-collapse. Yet, overall spinal alignment can still achieve favorable outcomes with current treatments, consistent with previous studies[ 7 ]. The depth of the screws was not associated with re-collapse in this study. Previous reports have examined long screws in spinal surgery. For instance, Matsukawa et al. found that in cortical bone trajectory-transforaminal lumbar interbody fusion (CBT-TLIF), the fusion group had significantly greater screw insertion depth than the non-fusion group, with a cutoff of 39.2% [ 23 ]. Hao et al. reported that in posterior fixation for lumbar fractures, long screws (with a % depth of ≥ 80% of the vertebral body) led to better vertebral restoration and sagittal stability than short screws (with a % depth of ≤ 60%)[ 24 ]. In this study, 13.4% (12/89) of screws exhibiting > 80% depth were located cephalad, and 9% (8/88) were located caudally; this is a lower percentage than that reported by Hao et al. (55.3% (36/65)). However, the fracture site in this study was the thoracolumbar transition area and included more than three intervertebral fixation ranges, which may explain these differences in results to some extent. Our study has several limitations. First, its retrospective design is susceptible to inherent biases (e.g., incomplete records). Also, the precision and reliability of research findings are impacted by sample size. Additionally, postoperative imaging was not performed in a standing position. For optimal alignment evaluation, a standing position is recommended. Another limitation is that we have only analyzed radiographic parameters as outcome measures. Further studies incorporating patient-reported outcome measures are warranted. Although the evaluation included the presence or absence of reoperation within 1 year after surgery, an assessment of bone fusion, including flexion-extension X-rays, was not conducted. An ongoing register-based randomized controlled trial, the SunBurst trial[ 25 ], is planned to evaluate the same measurements using a method similar to that of a secondary analysis. Conclusion In a working-age population, the HU value was significantly associated with early re-collapse after posterior spinal fixation for thoracolumbar burst fractures 3 months after surgery. Declarations Author Contribution JM and RF initiated the study, analyzed the data, and wrote the manuscript. FB, MK, and KD analyzed data and reviewed the manuscript. SB analyzed the data, authored the manuscript, and supervised the study. JW, SM, and TE reviewed the manuscript. PG supervised JM and RF, performed surgery, and wrote the manuscript. Acknowledgement We sincerely thank the Swedish Fracture Register for their support and collaboration. We would also like to express our deep gratitude to all patients who participated in this study and to all trauma hospitals involved in the research. 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Acta Orthop 93:256–263 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted 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. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-6376244","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":450370000,"identity":"6946637d-94a1-40db-9bf9-64817e1c1dea","order_by":0,"name":"Jabbar 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12:38:27","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6376244/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6376244/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":82300576,"identity":"290a9649-7c08-4d26-92f3-2b9b0cb52c1b","added_by":"auto","created_at":"2025-05-08 20:48:39","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":52048,"visible":true,"origin":"","legend":"\u003cp\u003eflowcharts\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6376244/v1/135e5479b78a8c68379fb8e0.jpg"},{"id":82300585,"identity":"bc083293-4f28-424c-a90f-3eaba836440c","added_by":"auto","created_at":"2025-05-08 20:48:39","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":149436,"visible":true,"origin":"","legend":"\u003cp\u003eThe measurement of the % depth of the screw insertions was defined as the ratio of the length of the screw in the vertebral body (A) to the length of the anteroposterior length of the vertebral body (B) on the axial CT plan Percentage (A/B×100).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6376244/v1/bf3a7985ac178ee14d38919f.png"},{"id":82300580,"identity":"15a13205-91af-43bc-b530-fbb5f54806ce","added_by":"auto","created_at":"2025-05-08 20:48:39","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":61601,"visible":true,"origin":"","legend":"\u003cp\u003eRadiographs on the thoracolumbar area immediately after posterior fixation (a) and 3 months later (b). Height of the collapsed vertebra body was measured at the anterior (AH) and posterior (PH) borders. Kyphosis angle (KA) and wedge angle (WA) were also measured\u003cstrong\u003e.\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6376244/v1/e05b780dbdc5799b05717705.jpg"},{"id":82301309,"identity":"9c4e4249-ab78-4848-9fa4-dd80e0756fda","added_by":"auto","created_at":"2025-05-08 20:56:39","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":29225,"visible":true,"origin":"","legend":"\u003cp\u003eComputed tomography images illustrating the measurement of the HU value in a series of axial views of L1 vertebrae.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6376244/v1/5e0c74835702b979b5d7858f.jpg"},{"id":83417560,"identity":"c7ed70dc-508f-4959-9ff7-6a9ce0760887","added_by":"auto","created_at":"2025-05-25 22:01:22","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":929709,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6376244/v1/d3f72005-4b04-4962-99b8-74b1baf4819b.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Hounsfield unit is associated with vertebral body re-collapse 3 months after surgery in working-age patients with a thoracolumbar burst fracture: A retrospective register-based cohort study","fulltext":[{"header":"Introduction","content":"\u003cp\u003eBurst fractures are compression fractures of the vertebral body, characterized by damage to the posterior vertebral wall and at least one of the end plates[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. They most commonly occur at the thoracolumbar junction, where the biomechanical forces are highest[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. Burst fractures account for almost 10\u0026ndash;20% of all thoracolumbar fractures and are most common in young males with high-energy trauma[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Burst fractures often lead to prolonged disability, chronic pain, and extended sick leave[\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Posterior instrumented fusion is the most commonly used approach for thoracolumbar burst fractures[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. Some surgeons, however, recommend anterior fusion for cases scoring\u0026thinsp;\u0026ge;\u0026thinsp;7 on the load sharing classification (LSC) [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e, \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. In recent years, the posterior approach alone has shown good outcomes and faster return-to-work than the combined anterior-posterior approach, which is particularly advantageous for working-age individuals[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eOne important complication of posterior approaches is the early postoperative re-collapse of a well-reduced vertebral body, which is associated with correction loss, posttraumatic kyphosis, implant failure, and revision surgery[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. Various strategies have been explored to prevent implant failure in posterior approaches, including vertebroplasty[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], calcium hydroxyapatite augmentation[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], and screw insertion into the fractured vertebral body[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Few studies have investigated factors associated with vertebral re-collapse after surgery for burst fractures. It has previously been reported that age at the time of surgery and preoperative body height loss were associated with re-collapse following posterior instrumented fusion for thoracolumbar burst fractures[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. This study investigates factors associated with early postoperative (3 months) collapse of thoracolumbar burst fractures in working-age (18\u0026ndash;66) people.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy population\u003c/h2\u003e \u003cp\u003eThis retrospective study included data from patients registered in the Swedish Fracture Register (SFR) between 2015 and 2019. The SFR is a nationwide quality register covering all fracture types in Sweden, with spinal fractures incorporated since 2015, classified by a modified AO Spine system for standardized data collection[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Patients of working age with a single-level thoracolumbar burst fracture between T10 and L3 treated with posterior fixation were included. Patients with co-existing fractures in the same level pedicles or adjacent posterior structures (lamina, transverse, or spinous processes) were eligible if the posterior tension band was patent or indeterminate. Exclusion criteria included neurological injury beyond a single-level root (spinal cord or cauda equina injury), low-energy trauma, and pathological fractures.\u003c/p\u003e \u003cp\u003eComorbidity variables (diabetes, heart disease, osteoporosis) and reoperations within 1 year were collected from the Swedish National Patient Register, maintained by the National Board of Health and Welfare[\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]. This was done by linking patient records using their unique social security numbers, allowing the register to identify relevant comorbidities based on ICD-10 codes recorded during any inpatient hospital stay or specialized outpatient visit.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eMedical image analysis\u003c/h3\u003e\n\u003cp\u003eMedical images were collected from the treating hospitals\u0026rsquo; radiological departments. Patients underwent computed tomography (CT) and/or magnetic resonance imaging (MRI) within 2 weeks of the injury, followed by CT immediately after surgery and X-ray or CT 3 months after surgery. CT and MRI scans were acquired in the supine position, while X-rays were taken in the lateral decubitus position. Thoracolumbar CT was performed using Siemens Somatom Definition Flash (Siemens AG, Germany) and Canon Aquilion Prime (Canon Medical Systems, Japan) in helical mode with 120 kVp, adaptive tube load, and a slice thickness of 0.6\u0026ndash;0.7 mm. Multiplanar reconstructions were generated in three orientations (1.0\u0026ndash;3.0 mm thickness). Images were stored and analyzed using the institutional PACS.\u003c/p\u003e \u003cp\u003eThe evaluation of Kyphosis and vertebral body height assessments were conducted following the methodology outlined by Tang et al.[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Measurements included (1) kyphosis angle (Cobb angle between the superior endplate of the upper vertebra and the inferior endplate of the lower vertebra), (2) wedge angle (angle between the superior and inferior endplates of the fractured vertebra), and (3) the ratio of anterior to posterior vertebral body height (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003e). These parameters were assessed preoperatively, immediately postoperatively, and at 3 months postoperatively. Re-collapse was defined as an anterior height loss of at least 20%[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. The adjusted anterior height was calculated using the height ratio of adjacent vertebrae on immediate postoperative and 3-month postoperative images.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBone quality was assessed using Hounsfield unit (HU) values from the L1 vertebral body, measured on preoperative 3D CT using an oval region of interest within the trabecular bone of the middle axial slice (Fig.\u0026nbsp;5). If L1 were fractured, L2 was used instead[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. The depth of pedicle screws within the vertebral body (% depth) was measured postoperatively based on previous described methods by Fujita et al.[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Measurements were taken bilaterally from the most cranial and caudal vertebrae within the fixation segment, and the mean % depth was calculated. To minimize potential observer errors, two independent orthopedic surgeons (SB and FB) not involved in the treatment of the study patients evaluated digital radiographs magnified twice. Intraclass correlation coefficients were assessed for kyphosis, wedge angles, body height, and HU values. The number of patients with screws inserted in the fractured vertebra was also evaluated.\u003c/p\u003e \u003cp\u003eBy using preoperative CT, the fracture was classified according to the LSC and a modified version of the 2013 AO spine injury classification system[\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Patients were divided into two groups based on their LSC score: 68 patients had an LSC score\u0026thinsp;\u0026ge;\u0026thinsp;7 and patients had an LSC score\u0026thinsp;\u0026lt;\u0026thinsp;7. The progression of the kyphosis angle, wedge angle, and A/P height ratio was then compared between the two groups.\u003c/p\u003e \u003cp\u003e \u003cb\u003eThe measurement of pull-out of\u003c/b\u003e \u003cb\u003epedicle screw\u003c/b\u003e \u003cb\u003efrom the vertebral body\u003c/b\u003e\u003c/p\u003e \u003cp\u003ePull-out measurements of the pedicle screws were assessed by comparing immediate postoperative and 3-month postoperative images. The most cranial and caudal screws at fixation levels were examined. For cases with CT scans at both time points, pull-out was defined as \u0026ge;\u0026thinsp;2 mm displacement on axial images, based on previous criteria[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]. When only lateral X-rays were available 3 months post-surgery, pull-out was evaluated against sagittal images from the immediate postoperative CT. Two orthopedic spine surgeons (JM and RF) independently conducted the assessment.\u003c/p\u003e\n\u003ch3\u003eSurgery\u003c/h3\u003e\n\u003cp\u003eAll patients underwent posterior instrumented stabilization with either an open or minimally invasive approach. Given the extant evidence, a pedicle screw should be inserted at least one level above and below the fracture vertebra[\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. All surgeries were performed by either a consultant orthopedic surgeon or a neurosurgeon specializing in spine surgery. The surgical procedure was performed within 2 weeks of the injury date.\u003c/p\u003e\n\u003ch3\u003eStatistics analysis\u003c/h3\u003e\n\u003cp\u003eA Shapiro-Wilk test was conducted to assess distributional characteristics. Normally distributed data were expressed as mean with standard deviation (SD) and non-normally distributed data as median with interquartile range (IQR). Mann-Whitney U tests were used to assess group differences for continuous variables; Fisher's exact test was computed for the comparison of proportions. Paired t-tests assessed differences in kyphosis angle, wedge angle, and A/P vertebral height ratio between preoperative and immediate postoperative measurements and between immediate postoperative and 3-month postoperative measurements. Multiple logistic regression analysis was performed to identify factors associated with re-collapse. A backward-forward stepwise regression was used, selecting variable combinations that minimized the Akaike information criterion. Inclusion criteria were based on univariate analyses, considering variables significant (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05) or approaching significance (p\u0026thinsp;\u0026lt;\u0026thinsp;0.2). Statistical analyses were performed using SPSS for Mac (version 29.0; IBM Corp., Armonk, NY, USA).\u003c/p\u003e\n\u003ch3\u003eEthics, funding, and potential conflict of interest\u003c/h3\u003e\n\u003cp\u003e The study adhered to the Helsinki Declaration's ethical principles and was approved by the Swedish Ethical Review Authority (Approval No: 2021-00011).\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eThe patient selection process for this study is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e1\u003c/span\u003e. A cohort of 100 patients with burst fractures was included. Their demographic characteristics are summarized in Table\u0026nbsp;1. Screws placed in the most cranial fixed vertebra tended to be inserted deeper into the vertebral body than those in the most caudal fixed vertebra. Based on the modified AO classification, the most common fracture type was A4-B0, accounting for 56% of cases, and L1 was the most frequent level for the fractures, accounting for 51% of cases. The median load sharing classification (LSC) score was 8, exceeding the threshold of 7, where anterior column reconstruction is generally recommended. Of the 100 patients, three underwent additional surgery within 1 year: one due to surgical site infection, one due to neurological deficits, and one due to implant failure.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003ePostoperative vertebral collapse\u003c/h3\u003e\n\u003cp\u003eThe data on the corrections angle achieved by the surgery, the progression of kyphosis, wedge angles, and the anterior/posterior height ratio (A/P ratio) of vertebra collapse are shown in Table\u0026nbsp;2. The immediate postoperative measurements revealed a reduction in the average kyphosis angle and wedge angle compared to their preoperative values, with the means decreasing from 10.7 to -2.3\u0026deg; and from 14.7 to 5.9\u0026deg;, respectively (p\u0026thinsp;\u0026lt;\u0026thinsp;0.0001 for both). However, vertebral collapse had progressed by the 3-month follow-up, leading to increases in both angles. At this later time point, the mean kyphosis angle had risen to 2.9\u0026deg; and the mean wedge angle to 10.3\u0026deg;. The progression of the angles over this period averaged 5.7\u0026deg; for kyphosis and 4.4\u0026deg; for the wedge angle (ps\u0026thinsp;\u0026lt;\u0026thinsp;0.0001 for both). The A/P ratios demonstrated a similar progression. While surgery effectively improved the vertebral A/P ratio, a slight collapse was observed during the 3-month follow-up. The average A/P ratio increased from 0.68 to 0.87 units postoperatively but decreased to 0.76 units at the 3-month follow-up, reflecting a progression of 0.1 (both ps\u0026thinsp;\u0026lt;\u0026thinsp;0.0001).\u003c/p\u003e\n\u003ch3\u003eEvaluation of screw pull-out\u003c/h3\u003e\n\u003cp\u003eIn this study, 95 cases were analyzed for screw pull-out after excluding five cases: two cases were excluded due to severe rotation observed on postoperative radiographs, which rendered evaluation impossible; one case involved rod breakage; one case had a dislodged set screw; and one case had a pedicle screw placed entirely outside the pedicle. These exclusions were implemented to ensure the reliability of the analysis. Of the 95 patients evaluated, 15 (15%) had screw pull-out within 3 months of surgery. Eight patients (8%) had pull-out in only the cranial screw, one (1%) in only the caudal screw, and six (6%) in both.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e\u003cb\u003eComparisons between patients with and without re-collapse\u003c/b\u003e\u003c/h2\u003e \u003cp\u003eSixteen patients had radiographic vertebral re-collapse 3 months after surgery. Compared to the non-re-collapse group, the re-collapse group had a significantly higher proportion of females (56.3% vs. 43,7.1%, p\u0026thinsp;=\u0026thinsp;0.02) and lower HU values (160 vs. 197.5, p\u0026thinsp;=\u0026thinsp;0.02). Additionally, the re-collapse group showed significantly greater progression in KA (11.8 vs. 4.5, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), WA (10.4 vs. 3.3, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001), and A/P vertebral height loss (0.23 vs. 0.08, p\u0026thinsp;\u0026lt;\u0026thinsp;0.001) compared to the non-re-collapse group (Table\u0026nbsp;3).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003eMultiple logistic regression analysis of potential factors associated with re-collapse\u003c/h2\u003e \u003cp\u003eA multiple logistic regression analysis was conducted to examine the association between potential factors and the re-collapse of the fractured vertebra 3 months after surgery. A statistically significant association was observed between HU value and re-collapse (odds ratio [OR]: 0.97; 95% confidence interval [CI]: 0.94\u0026ndash;0.99). Preoperative LSC also showed a tendency to be associated with re-collapse (OR: 2.35, 95% CI: 1.07\u0026ndash;6.82, p\u0026thinsp;=\u0026thinsp;0.06). No statistically significant association with screw insertion depth or the number of fixed vertebrae was observed (Table\u0026nbsp;4).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section2\"\u003e \u003ch2\u003eComparison of vertebral collapse at 3 months postoperatively between LSC\u0026thinsp;\u0026ge;\u0026thinsp;7 and LSC\u0026thinsp;\u0026lt;\u0026thinsp;7\u003c/h2\u003e \u003cp\u003eWe compared the progression of the kyphosis angle, wedge angle, and A/P height ratio between patients with LSC scores\u0026thinsp;\u0026ge;\u0026thinsp;7 and LSC scores\u0026thinsp;\u0026lt;\u0026thinsp;7. Sixteen patients had LSC scores\u0026thinsp;\u0026lt;\u0026thinsp;7 and 68 had LSC scores\u0026thinsp;\u0026ge;\u0026thinsp;7. There was a significant difference in wedge angle and A/P height ratio between the two groups (both ps\u0026thinsp;=\u0026thinsp;0.04), while there was no statistically significant difference in kyphosis angle (p\u0026thinsp;=\u0026thinsp;0.5) (Table\u0026nbsp;5).\u003c/p\u003e \u003c/div\u003e"},{"header":"Discussion","content":"\u003cp\u003eOur major finding demonstrated a significant association between lower HU values and early re-collapse following posterior spinal fixation in patients with thoracolumbar burst fractures, including those of working age. Meanwhile, screw insertion depth and the number of fixation levels were not associated with early re-collapse. Kohno et al. reported a 29% re-collapse rate among patients aged 60\u0026ndash;86. The authors concluded that although posterior fixation yielded favorable clinical outcomes, the high incidence of postoperative complications due to bone fragility persisted[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]. Our study examined working-age adults, of whom only three were diagnosed with osteoporosis. A recent report defined normal lumbar HU values as \u0026ge;\u0026thinsp;170 and osteoporotic values as \u0026le;\u0026thinsp;115. The average L1 HU in this study was 190, indicating a relatively healthy population[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]. Despite this, a statistically significant association persisted between HU values and re-collapse, suggesting that a larger-scale study is warranted to establish a re-collapse HU threshold independent of osteoporosis. Additionally, it indicates the importance of postoperative bone quality assessment even in this age group.\u003c/p\u003e \u003cp\u003ePreoperative LSC tended to be associated with re-collapse. The LSC was originally developed to predict screw breakage or indicate the need for anterior reconstruction; its development was based on older-generation Steffe plates and screws, without considering soft tissue damage[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Subsequent research has shown that posterior instrumentation alone may suffice, even in cases with high LSC scores, with no clear correlation between LSC and instrumentation failure or correction loss[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Patients with an LSC score of \u0026ge;\u0026thinsp;7 had significantly greater progression of wedge angle and A/P height ratio than those with an LSC score of \u0026lt;\u0026thinsp;7. However, there was no difference in the progression of the kyphosis angle. This observation suggests that, despite severe burst fractures with high LSC scores, posterior reconstruction alone may lead to vertebral re-collapse. Yet, overall spinal alignment can still achieve favorable outcomes with current treatments, consistent with previous studies[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe depth of the screws was not associated with re-collapse in this study. Previous reports have examined long screws in spinal surgery. For instance, Matsukawa et al. found that in cortical bone trajectory-transforaminal lumbar interbody fusion (CBT-TLIF), the fusion group had significantly greater screw insertion depth than the non-fusion group, with a cutoff of 39.2% [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. Hao et al. reported that in posterior fixation for lumbar fractures, long screws (with a % depth of \u0026ge;\u0026thinsp;80% of the vertebral body) led to better vertebral restoration and sagittal stability than short screws (with a % depth of \u0026le;\u0026thinsp;60%)[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. In this study, 13.4% (12/89) of screws exhibiting\u0026thinsp;\u0026gt;\u0026thinsp;80% depth were located cephalad, and 9% (8/88) were located caudally; this is a lower percentage than that reported by Hao et al. (55.3% (36/65)). However, the fracture site in this study was the thoracolumbar transition area and included more than three intervertebral fixation ranges, which may explain these differences in results to some extent.\u003c/p\u003e \u003cp\u003eOur study has several limitations. First, its retrospective design is susceptible to inherent biases (e.g., incomplete records). Also, the precision and reliability of research findings are impacted by sample size. Additionally, postoperative imaging was not performed in a standing position. For optimal alignment evaluation, a standing position is recommended. Another limitation is that we have only analyzed radiographic parameters as outcome measures. Further studies incorporating patient-reported outcome measures are warranted. Although the evaluation included the presence or absence of reoperation within 1 year after surgery, an assessment of bone fusion, including flexion-extension X-rays, was not conducted. An ongoing register-based randomized controlled trial, the SunBurst trial[\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e], is planned to evaluate the same measurements using a method similar to that of a secondary analysis.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn a working-age population, the HU value was significantly associated with early re-collapse after posterior spinal fixation for thoracolumbar burst fractures 3 months after surgery.\u003c/p\u003e "},{"header":"Declarations","content":"\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eJM and RF initiated the study, analyzed the data, and wrote the manuscript. FB, MK, and KD analyzed data and reviewed the manuscript. SB analyzed the data, authored the manuscript, and supervised the study. JW, SM, and TE reviewed the manuscript. PG supervised JM and RF, performed surgery, and wrote the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eWe sincerely thank the Swedish Fracture Register for their support and collaboration. We would also like to express our deep gratitude to all patients who participated in this study and to all trauma hospitals involved in the research.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eHoldsworth F (1970) Fractures, dislocations, and fracture-dislocations of the spine. J Bone Joint Surg Am 52(8):1534\u0026ndash;1551\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWood KB et al (2014) Management of thoracolumbar spine fractures. Spine J 14(1):145\u0026ndash;164\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGnanenthiran SR, Adie S, Harris IA (2012) Nonoperative versus operative treatment for thoracolumbar burst fractures without neurologic deficit: a meta-analysis. 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Spine (Phila Pa 1976) 19(15):1741\u0026ndash;1744\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eStam WT et al (2020) The Predictive Value of the Load Sharing Classification Concerning Sagittal Collapse and Posterior Instrumentation Failure: A Systematic Literature Review. Global Spine J 10(4):486\u0026ndash;492\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHinojosa-Gonzalez DE et al (2023) A Network Meta-Analysis on the Surgical Management of Thoracolumbar Burst Fractures: Anterior, Posterior, and Combined. Spine Surg Relat Res 7(3):211\u0026ndash;218\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJang HD et al (2018) Risk factor analysis for predicting vertebral body re-collapse after posterior instrumented fusion in thoracolumbar burst fracture. Spine J 18(2):285\u0026ndash;293\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCho DY, Lee WY, Sheu PC (2003) \u003cem\u003eTreatment of thoracolumbar burst fractures with polymethyl methacrylate vertebroplasty and short-segment pedicle screw fixation.\u003c/em\u003e Neurosurgery, 53(6): pp. 1354-60; discussion 1360-1\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMarco RA, Meyer BC, Kushwaha VP (2010) Thoracolumbar burst fractures treated with posterior decompression and pedicle screw instrumentation supplemented with balloon-assisted vertebroplasty and calcium phosphate reconstruction. Surgical technique. J Bone Joint Surg Am 92(Suppl 1 Pt 1):67\u0026ndash;76\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGuven O et al (2009) The use of screw at the fracture level in the treatment of thoracolumbar burst fractures. J Spinal Disord Tech 22(6):417\u0026ndash;421\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKanna RM, Shetty AP, Rajasekaran S (2015) Posterior fixation including the fractured vertebra for severe unstable thoracolumbar fractures. Spine J 15(2):256\u0026ndash;264\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMorgonsk\u0026ouml;ld D et al (2019) Inter- and intra-rater reliability of vertebral fracture classifications in the Swedish fracture register. World J Orthop 10(1):14\u0026ndash;22\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eM\u0026ouml;ller M et al (2022) The Swedish Fracture Register - ten years of experience and 600,000 fractures collected in a National Quality Register. BMC Musculoskelet Disord 23(1):141\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLudvigsson JF et al (2011) External review and validation of the Swedish national inpatient register. BMC Public Health 11:450\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTeng MM et al (2003) Kyphosis correction and height restoration effects of percutaneous vertebroplasty. AJNR Am J Neuroradiol 24(9):1893\u0026ndash;1900\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAnderson PA et al (2018) Clinical Use of Opportunistic Computed Tomography Screening for Osteoporosis. J Bone Joint Surg Am 100(23):2073\u0026ndash;2081\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFujita R et al (2024) Real-world clinical accuracy of long cortical bone trajectory screw placement using a patient-specific template guide. J Spine Surg 10(3):468\u0026ndash;478\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSumiya S et al (2021) Comparative analysis of clinical factors associated with pedicle screw pull-out during or immediately after surgery between intraoperative cone-beam computed tomography and postoperative computed tomography. BMC Musculoskelet Disord 22(1):55\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKohno M et al (2019) Surgical Intervention for Osteoporotic Vertebral Burst Fractures in Middle-low Lumbar Spine with Special Reference to Postoperative Complications Affecting Surgical Outcomes. Neurol Med Chir (Tokyo) 59(3):98\u0026ndash;105\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCourtois EC, Ohnmeiss DD (2025) Assessing bone quality in hounsfield units using computed tomography: what value should be used to classify bone as normal or osteoporotic? Eur Spine J 34(2):493\u0026ndash;497\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMatsukawa K et al (2021) Depth of vertebral screw insertion using a cortical bone trajectory technique in lumbar spinal fusion: radiological significance of a long cortical bone trajectory. J Neurosurg Spine, : p. 1\u0026ndash;6\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiu H et al (2020) Effects of pedicle screw number and insertion depth on radiographic and functional outcomes in lumbar vertebral fracture. J Orthop Surg Res 15(1):572\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBlixt S et al (2022) Study protocol: The SunBurst trial-a register-based, randomized controlled trial on thoracolumbar burst fractures. Acta Orthop 93:256\u0026ndash;263\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-6376244/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6376244/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cb\u003ePurpose\u003c/b\u003e\u003c/p\u003e \u003cp\u003eFactors associated with early re-collapse after posterior fixation of thoracolumbar burst fractures have been sparsely examined in previous studies. We investigated the factors associated with re-collapse within the first 3 months after posterior fixation of thoracolumbar burst fractures.\u003c/p\u003e\u003cp\u003e\u003cb\u003eMethods\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThis retrospective study used data from the Swedish Fracture Register (2015\u0026ndash;2019), encompassing patients aged 18 to 66 who sustained a single-level thoracolumbar burst fracture between T11 and L3 and underwent posterior fixation. The fractures were classified by a modified AO classification and the load sharing classification (LSC). Hounsfield unit (HU) values were used to evaluate bone quality. Vertebral collapse assessment included measurements of the kyphosis angle, wedge angle, and anterior/posterior height. Moreover, pull-out of pedicle screws was assessed. Multiple logistic regression analysis assessed the factors associated with re-collapse within 3 months after surgery\u003c/p\u003e\u003cp\u003e\u003cb\u003eResults\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThis study comprised 100 participants, of whom 58 were male and 42 were female. Some 16 patients had radiographic vertebral re-collapse and 15 had pedicle screw pull-out. A statistically significant association was observed between HU values and re-collapse (odds ratio [OR]: 0.97, 95% confidence interval [CI]: 0.94\u0026ndash;0.99). Preoperative LSC also tended to be associated with re-collapse (OR: 2.35, 95% CI: 1.07\u0026ndash;6.82). However, no association with screw insertion depth or the number of fixated vertebrae was seen in this study.\u003c/p\u003e\u003cp\u003e\u003cb\u003eConclusion\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThree months post-surgery, a statistically significant association was noted between HU values and early re-collapse after posterior spinal fixation in patients with thoracolumbar burst fractures.\u003c/p\u003e","manuscriptTitle":"Hounsfield unit is associated with vertebral body re-collapse 3 months after surgery in working-age patients with a thoracolumbar burst fracture: A retrospective register-based cohort study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-05-08 20:48:34","doi":"10.21203/rs.3.rs-6376244/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"45236823-3068-4b5e-8741-02833b963a73","owner":[],"postedDate":"May 8th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2025-05-25T21:53:16+00:00","versionOfRecord":[],"versionCreatedAt":"2025-05-08 20:48:34","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6376244","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6376244","identity":"rs-6376244","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}