Diagnosis and treatment of Pipkin type IV femoral head fracture: a finite element analysis

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Methods Finite element models of normal hip joints and Pipkin type IV femoral head fractures were separately established, and the stress distribution and displacement of each model were simulated using finite element analysis. Clinical data were retrospectively collected from 15 patients with Pipkin type IV femoral head fractures who underwent surgical treatment at Xijing Hospital, Air Force Medical University, between March 2013 and April 2019. Their hip joint function was evaluated during follow-up, and the findings from the finite element analysis were validated through comparison with the clinical follow-up results. Results The results of the finite element analysis were as follows: (1) When a load is applied to the normal hip joint model in the upright position, the femoral head bears the largest stress, followed by the posterior wall and top of the acetabulum, and the anterior column of the acetabulum experiences the largest displacement, followed by the femoral neck, which suggests that Pipkin type IV femoral head fractures are prone to occur when the lower limbs hit the ground after falling from a height. When a load is applied to the normal hip joint model in 90°, 120° flexion and 10° internal rotation, the stress is concentrated on the top and posterior wall of the acetabulum and the femoral neck and the displacement is mainly distributed along the posterior column and posterior wall of the acetabulum, which indicates that the patient is prone to Pipkin type IV femoral head fracture if the dashboard is damaged in a car accident. (2) In the model of Pipkin type IV femoral head fracture, acetabular fractures are fixed with lag screws and reconstruction plates, resulting in the smallest stress and displacement, which suggests that this method of internal fixation is the most reliable. The clinical follow-up results were as follows: a total of 15 patients were followed up for 12–86 months, with a mean of 34.4 months and Majeed functional scoring was performed to evaluate the hip joint at the last follow-up after their femoral head fractures were fixed with double-head compression screws. Among them, 5 cases of acetabular fracture were fixed with lag screws and reconstruction plates, and their hip joint function was graded excellent; 5 cases of acetabular fracture were fixed with reconstruction plates, and their hip joint function was graded good; another 5 cases of acetabular fractures were fixed with lag screws, and their hip joint function was graded as good. Conclusion The results of finite element analysis in the normal hip joint model are consistent with the clinicaldata of patients with injuries caused by falling from a height and car accidents, so finite element analysis can provide evidence for the early diagnosis of Pipkin type IV femoral head fractures. The results of the finite element analysis in the model of Pipkin type IV femoral head fracture with internal fixation are consistent with the hip function scores in the clinical evaluation, so finite element analysis can provide guidance for selecting optimal internal fixation. In short, finite element analysis can play an important role in the clinical diagnosis and treatment of Pipkin type IV femoral head fractures. finite element analysis femoral head fracture Pipkin type IV diagnosis treatment Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1. Introduction Pipkin type IV femoral head fracture refers to femoral head fracture associated with posterior dislocation of the hip joint and ipsilateral acetabular fracture [ 1 ] . Pipkin type IV femoral head fracture is a high-energy injury characterized by its severity and complexity, difficulty in management and high complication rate [ 2 ] . Some physicians categorize it as a floating hip injury [ 3 , 4 ] . There is no consensus on the diagnosis and treatment of Pipkin type IV femoral head fracture. As the most important weight-bearing joint of the human body, the hip joint plays an important role in the upright standing and movement of the human body. Due to its anatomy, complex functions and deep location of the hip joint, it is difficult to carry out in vivo mechanical studies, and the reliability of animal model experiments is uncertain. Finite element analysis, one key method applied in computer mechanics analysis, is widely applied in bone biomechanics, especially for the mechanical analysis of irregular structures. This study adopted finite element analysis and biomechanics to analyze the injury mechanism of Pipkin type IV femoral head fracture, bone stress and displacement during surgical treatment of internal fixation and verified the results of the finite element analysis with the clinical data of patients with these types of fractures in Xijing Hospital of Air Force Medical University to provide a theoretical basis for clinical decision-making. 2. Materials & Methods 1 General data In total, 15 patients with Pipkin type IV femoral head fractures treated at Xijing Hospital from March 2013 to April 2019 were involved in this study, including 11 men and 4 women. They were 27–70 years, mean 50.6 years. There were 7 cases of car accident injuries, 4 cases of fall injuries and 4 cases of other types. The inclusion criteria were as follows: (1) diagnostic criteria for Pipkin type IV femoral head fracture and (2) surgical treatment. The exclusion criteria were as follows: (1) patients with pathological fractures or patients who underwent conservative treatment; and (2) patients who were lost to follow-up. 2. Methods 1. The normal hip joint model and Pipkin type IV fracture femoral head model were established, and finite element analysis was used to simulate the stress distribution and displacement of each model. 1.1 Establishment of the three dimensional solid models The CT images of healthy volunteers were imported into Mimics software(Fig. 1a), and the tissues were segmented into two-dimensional images to obtain the solid model of each bone and then imported into GeomagicStudio 2015 for smoothing. The STP file was exported last (Fig. 1b). The STP file was imported into the UG10.0 software. The articular cartilage, fracture model and internal plants were designed according to the requirements, and then the STP files of each model were exported.(Fig. 1c and Fig. 1d) The STP file was imported into hypermesh14.0 software to mesh the model, and finite element models of the nondestructive hip joint (Fig. 2a), posterior wall fracture of the acetabulum, femoral head fracture, and Pipkin type IV femoral head fracture were obtained (Fig. 2b). The total number of nodes and units in each model was showed in Table 1(a). 1.3 Material property assignment Each element in the mesh should be assigned material properties, including the bone, cartilage, and internal fixators. To verify the results, the properties of the mechanical materials were set according to the previous literature. The elastic modulus of the cortical bone material was uniformly set to 10000 MPa, with a Poisson's ratio of 0.29 and cancellous bone of 100 MPa, with a Poisson's ratio of 0.29. Articular cartilage was defined as a linear elastic material, with an elastic modulus of 12 MPa and a Poisson’s ratio of 0.4. The material of the prosthetic implant was TC4, with an elastic modulus of 110000 MPa and a Poisson’s ratio of 0.3 (Table 1(b)). 1.4 Boundary settings The boundary conditions were defined as follows: hard sliding contact was defined between the fracture blocks and between the steel plate and bones; bound contact constraints were defined between the screws and bone and between the screws and plate and between the acetabular cortical bone and cartilage; and sliding contact was defined between the femoral head and acetabular cartilage. Contact property: frictional contact; friction coefficient = 0.01; calculation: penalty function method. 1.5 Loading The pubic symphysis was fixed without displacement or rotation in any direction (U1 = U2 = U3 = UR1 = UR2 = UR3 = 0), and the auricular surface of the sacroiliac joint was constrained (U1 = U2 = U3 = UR1 = UR2 = UR3 = 0). In the upright position, 350 N, 550 N, 750 N, 950 N, and 1500 N loads were applied along the femoral axis; at 10° internal rotation, a load of 750 N was applied along the femoral axis in 90° and 120° flexion. 1.6 Finite element analysis In the model of the normal hip joint, different loads were applied in the upright position to simulate the situation in which the lower limbs hit the ground after falling from a height(Fig. 3a), and a load was applied at different angles in flexion to simulate the damage of the dashboard in a car accident (Fig. 3b). When the normal hip joint model is loaded in the upright position, the stress is concentrated on the longitudinal axis of the iliac bone, the anterior wall of the acetabulum, the top and posterior wall of the acetabulum, the suprapubic branch, the weight-bearing area of the femoral head, the pressure side of the femoral neck, and the femoral distance. The femoral head bears the largest stress, followed by the posterior wall and the top of the acetabulum. The displacement was mainly distributed on the anterior column of the acetabulum, the anterior wall of the acetabulum, the top, posterior wall and posterior column of the acetabulum, the weight-bearing area of the femoral head, the femoral neck, and the intertrochanteric area (Fig. 3c). This suggests that Pipkin type IV femoral head fractures are prone to occur when the lower limbs hit the ground after falling from a height. When a load is applied to the normal hip joint model in flexion, the stress is concentrated on the top and posterior wall of the acetabulum and the femoral neck; the displacement is mainly distributed on the posterior wall of the acetabulum and the intertrochanteric area (Fig. 3d), which indicates that the patient is prone to a Pipkin type IV femoral head fracture if the dashboard is damaged in a car accident. We carried out a classification and comparison of Pipkin type IV femoral head fracture models: all femoral head fractures were fixed with double-head compression screws, and the acetabular fractures were fixed with three different methods: lag screws combined with reconstruction plates, reconstruction plates alone, and lag screws alone. Different loads were applied in the upright position of the joint to simulate the situation in the standing position, and loads at different angles were applied in flexion to simulate the situation during walking. In the model of Pipkin type IV femoral head fracture under a load of 750 N in the upright position, when the acetabular fracture was fixed using a combination of lag screws and reconstruction plates, the stress values were 50.73 MPa with a displacement of 0.059 mm in the ilium, and 30.58 MPa with a displacement of 0.284 mm in the femur (Fig. 4a–4d, Fig. 7a, Table 2c). When fixation was performed with reconstruction plates alone, the stress reached 77.16 MPa with a displacement of 0.175 mm in the ilium, and 74.30 MPa with a displacement of 0.785 mm in the femur (Fig. 6a–6c, Table 3a). With lag screws alone, the stress was 87.69 MPa and displacement was 0.187 mm in the ilium, while in the femur the values were 54.74 MPa and 0.689 mm, respectively (Fig. 6a–6c, Table 3b). Under an increased load of 1500 N in the upright position, fixation with both lag screws and reconstruction plates resulted in a stress of 50.44 MPa and displacement of 0.355 mm in the ilium, and 55.4 MPa with 0.638 mm displacement in the femur (Fig. 4a–4d, Table 2b). When only reconstruction plates were used, the stress was 85.08 MPa with 0.849 mm displacement in the ilium, and 146.1 MPa with 1.562 mm displacement in the femur (Fig. 6a–6c, Table 6). With lag screws alone, the ilium showed a stress of 141.7 MPa and displacement of 0.875 mm, while the femur exhibited 87.14 MPa and 0.957 mm displacement (Fig. 5a–5d, Table 3b). These results indicate that the model with acetabular fracture fixed using a combination of lag screws and reconstruction plates exhibited the lowest stress and displacement under varying load conditions (Fig. 7). A consistent trend was observed under other load levels of 350 N, 550 N, and 950 N (Table 2a–2c). In summary, for the fixation of acetabular fractures, the combined use of lag screws and reconstruction plates provides superior biomechanical stability compared to the use of either reconstruction plates or lag screws alone. For the model of the Pipkin IV femoral head fracture under a load of 750 N in flexion, taking Q30° flexion for example, if the acetabular fracture was fixed with lag screws and reconstruction plates, the stress was 81.93 mpa and the displacement was 0.202 mm in the ilium, 62.09 mpa and 4.621 mm in the femur; if the acetabular fracture was fixed with reconstruction plates, the stress was 144.9 mpa and the displacement was 0.465 mm in the ilium, 96.51 mpa and 7.992 mm in the femur; if the acetabular fracture was fixed with lag screws, the stress was 364.3 mpa and the displacement was 0.505 mm in the ilium, 87.60 mpa and 7.887 mm in the femur (Fig. 7, Table 3). The overall trend of bone stress and displacement data in the finite element analysis was consistent with that in the upright position (Fig. 7), suggesting that fixation with lag screws and reconstruction plates was the most effective for acetabular fractures. 2 Case collection and follow-up In accordance with the diagnostic criteria of Pipkin type IV femoral head fracture and the inclusion and exclusion criteria of this study, 15 cases were collected from the Keep running scientific research management system and the quality control system of electronic medical records. All patients were followed up by telephone, WeChat or other contact methods. Some patients were followed up by regular visits in the outpatient clinic, and some patients were followed up at home. During the follow-up, patients were checked by X-rays to observe fracture healing, photos or videos were taken to observe postoperative functional recovery, and the Majeed standard functional scoring system was used to evaluate the hip joint function and quantify functional recovery. 3. Results Finite element analysis results When a load is applied to the normal hip joint model in the upright position, the stress is concentrated on the longitudinal axis of the ilium, the anterior wall of the acetabulum, the top and posterior wall of the acetabulum, the suprapubic branch, the weight-bearing area of the femoral head, the pressure side of the femoral neck, and the femoral distance. The femoral head and neck bear the largest stress, followed by the posterior wall and top of the acetabulum; the displacement is mainly distributed on the anterior column of the acetabulum, the anterior wall of the acetabulum, the top, posterior wall and posterior column of the acetabulum, the weight-bearing area of the femoral head, the femoral neck, and the intertrochanteric area. The anterior column of the acetabulum has the largest displacement, followed by the femoral head and neck. This suggests that Pipkin type IV femoral head fractures are prone to occur when the lower limbs hit the ground after falling from height. When a load is applied to the normal hip joint model in 90°, 120° flexion and 10° internal rotation, the stress is concentrated on the top and posterior wall of the acetabulum and the femoral head and neck; the displacement is mainly distributed along the posterior column and posterior wall of the acetabulum, which indicates that the patient is prone to a Pipkin type IV femoral head fracture if the dashboard is damaged in a car accident. In a model of Pipkin type IV femoral head fracture, the femoral head is fixed with double-head compression screws, and acetabular fractures are fixed with lag screws and reconstruction plates, resulting in the smallest stress and displacement, which suggests that this method of internal fixation is the most reliable. Clinical follow-up results A total of 15 patients were followed up for 12–86 months, with a mean of 34.4 months. There were 7 cases of traffic accident injuries, 4 cases of falling injuries, and 4 cases of other types. Majeed functional scoring was performed to evaluate the hip joint at the last follow-up: 15 cases of femoral head fractures were fixed with double-head compression screws. Among them, 5 cases of acetabular fracture were fixed with lag screws and reconstruction plates, and their hip joint function was graded excellent; 5 cases of acetabular fracture were fixed with reconstruction plates, and their hip joint function was graded good; another 5 cases of acetabular fractures were fixed with lag screws, and their hip joint function was graded good. 4. Conclusion The results of finite element analysis in the normal hip joint model are consistent with clinical data in patients with injuries caused by falling from a height and car accidents. The results of the finite element analysis in the model of Pipkin type IV femoral head fracture with internal fixation were consistent with hip function scores in the clinical evaluation. In conclusion, finite element analysis can provide a theoretical basis for exploring the injury mechanism of Pipkin type IV femoral head fractures and provide data support for selecting the optimal internal fixation method, which is beneficial for the clinical diagnosis and treatment of Pipkin type IV femoral head fractures. 5. Discussion 1. Development of finite element analysis Finite element analysis (FEA) [ 5 – 7 ] refers to the application of the matrix method in structural mechanics and elastic mechanics. Brekelmans et al. [ 8 ] first applied the finite element method in orthopedics in 1972. At present, finite element analysis has been used in bone stress analysis, fixator selection, optimal design and the working life prediction of joint prostheses. In particular, it is mostly applied in the biomechanics of the spine [ 9 , 10 ] , including detecting pressure changes during joint motion within the spine, selecting materials for spinal internal fixation and surgical methods, and bone stress analysis of the limbs [ 11 ] (the ankle joint, knee joint, elbow, etc.). Moreover, it is also involved in studies on the pathological mechanism of certain diseases, e.g., plantar stress distribution in diabetic foot patients [ 12 ] and the design of artificial joint prostheses, e.g., hip replacement prostheses [ 13 , 14 ] . Finite element analysis has achieved a leap from two-dimensional to three-dimensional. With the development of computer technology and accurate analysis programs, finite element analysis is not confined to simple stress analysis. The combination of the finite element method and digital technology makes the establishment of models more accurate and convenient. Thanks to the advances in biomechanics and computer software, finite element analysis has great potential for applications in orthopedic biomechanics, especially for studies on the pathogenesis of degenerative diseases [ 15 , 16 ] and the development and selection of internal or external fixation materials [ 17 ] . 2. Floating hip injury and Pipkin type IV femoral head fracture Floating hip injury (FHI) was first proposed by Liebergall et al. [ 18 ] and was defined as an unstable pelvic fracture or acetabular fracture caused by high-energy violence accompanied by an ipsilateral femoral fracture [ 19 ] . Based on Tile’s classification of pelvic fractures [ 20 ] , Liebergall et al. [ 18 ] divided floating hip injuries into 3 types. Muller’s classification is also commonly applied in the clinic [ 19 ] . Muller’s classification and Liebergall’s classification are widely used in clinical practice, but neither has evaluated the subdivision of femoral fractures. Floating hip injury is a kind of floating joint injury that refers to extra-articular or intra-articular fracture of the upper and lower bones adjacent to the joint [ 21 ] . Accordingly, femoral fractures in floating hip injuries can be subdivided into proximal femoral fractures, femoral shaft fractures, and distal femoral fractures. Because of the involvement of hip joints, those with acetabular fractures or femoral head fractures can be regarded as intra-articular floating hip injuries, among which Pipkin type IV femoral head fracture (i.e., acetabular fracture) combined with ipsilateral femoral head fracture and dislocation is the most severe in the clinic. Pipkin type IV femoral head fracture has a lot in common with floating hip injury, including the injury mechanism, cause of violence, treatment principles and complications; therefore, it is considered one type of floating hip injury. An epidemiological survey on floating hip injury by Zhang et al. [ 22 ] revealed that the most common type of floating hip injury is the Muller A type [ 19 ] , and floating hip injuries with proximal fractures of the ipsilateral acetabulum and femoral head are the most common in the clinic. In other words, the Pipkin type IV femoral head fracture is the most common type of floating hip injury. In this study, we established a finite element model of Pipkin type IV femoral head fracture with internal fixation and performed a mechanical analysis, which was of clinical significance for the treatment of floating hip injuries. 3. Application of finite element analysis of Pipkin type IV femoral head fractures If the hip joint is seriously traumatized, it is prone to severe consequences, such as femoral head necrosis or traumatic arthritis [ 23 ] . Due to the limited source of the specimens and the difficulty in controlling the experimental conditions, biomechanics experiments on hip joints are restricted [ 24 ] . Finite element analysis has good adaptability to the complex structure of the hip joint. It can simulate many clinical conditions by changing the parameters and analyze the mechanical changes of the hip joint in the physiological and pathological processes [ 9 , 25 ] . Most femoral head fractures are caused by high-energy injuries. The surgery is difficult and demanding, and choosing an appropriate fixation method is a key step to ensure its efficacy [ 10 ] . In view of the complexity and severity of Pipkin type IV femoral head fracture, there is no strong evidence about its treatment or quality evaluation, especially for the effect of internal fixation on postoperative joint function. Finite element analysis can play an irreplaceable role in the diagnosis and treatment of Pipkin type IV femoral head fractures. 4. Precautions for the application of finite element analysis The purpose of finite element analysis is to provide a biomechanical and theoretical basis for clinical applications. Existing modeling methods cannot achieve an absolute real simulation. Therefore, accurate modeling is the primary prerequisite to ensure the authenticity and reliability of simulation data. In addition, human errors in load and boundary condition settings, cell division, node selection, and elastic modulus settings can also affect the authenticity and reliability of the research data, which requires a rigorous scientific attitude and the meticulousness of researchers, as well as careful planning and arrangement. Finite element analysis requires pure theoretical research. The results of theoretical research are generally based on tendencies and qualitative perspectives. We need to minimize human errors and improve the reliability of research data and at the same time, the results of finite element analysis need to be compared, verified and comprehensively analyzed with in vivo or in vitro experiments, animal experiments and clinical observations to ensure the conscientiousness and reliability of the scientific research [ 7 ] . In this study, the results of finite element analysis of related models were confirmed by clinical follow-up data of patients with Pipkin type IV femoral head fractures, so the conclusion is reliable. 5. Disadvantages and prospects of the finite element analysis Finite element analysis can fully control the experimental conditions and simulate the biomechanical experiments to the greatest extent by computers, which play a bridging role in the transitional stage from animal experiments to clinical human specimen experiments [ 11 ] . However, finite element analysis also shows the following disadvantages [ 10 , 26 , 27 ] : (1) finite element technology belongs to engineering mechanics, and its calculation requires a strong capability of mathematical logic and reasoning, which hampers its application; (2) in cases of Pipkin type IV femoral head fractures, the shape of the femoral head and acetabulum is irregular, so it is difficult to accurately simulate internal stress distribution with an elastic modulus of finite element cells. Both the experimental data and approximation can affect the accuracy; (3) the motion system of the human body is both dynamic and static, e.g., the hip joint has a three-dimensional axis of movement, undertaking a complex range of motion, such as external rotation, external abduction, internal rotation, adduction, flexion and extension [ 10 , 28 ] . The mechanism of Pipkin type IV femoral head fracture and postoperative functional recovery should be investigated during the state of motion, and only in this way can the results be more realistic. Finite element analysis is insufficient in studying the stress distribution and displacement of the bone and joint in motion, which is the direction of future studies [ 11 ] . Declarations Acknowledgments None Author contributions All authors participated in the conception and design of this study.Yefan Zhang,Jiahao Zeng , and Mwnglong Wang contributed to data collection and analysis. Yefan Zhang writed the first draft of the manuscript. Qiyou Cao, along with Haifeng Dang, Long Bi, Zhuojing Luo, completed the design and correction of the chart. Junjun Fan, Donglin Li and Haifeng Dang revised the manuscript. All authors read and agreed to the final manuscript. Funding None Ethics approval and consent to participate The study was approved by the Ethics Committee of Xijing Hospital of Military Medical University (approval No. QX20221008-1), and the need for informed consent was waived by the ethics committee. All procedures involving human participants in this study were conducted in accordance with the principles of the Declaration of Helsinki. Clinical trial number Not applicable Consent for publication Not applicable Competing interests The authors declare no competing interests Author details 1Department of Orthopedics, Xijing Hospital of Military Medical University (Xi 'an, 710032),China . Email:fanjunjunys＠163.com [email protected] References Pipkin G. Treatment of grade IV fracture-dislocation of the hip[J]. J Bone Joint Surg Am, 1957,39-a(5):1027–1042 passim. Wang SX, Li BH, Li J, et al. Middle-term follow-up results of Pipkin type IV femoral head fracture patients treated by reconstruction plate and bioabsorbable screws[J]. 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Tables Tables 1 to 3 are available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files Tables.docx Cite Share Download PDF Status: Published Journal Publication published 07 Jan, 2026 Read the published version in BMC Musculoskeletal Disorders → Version 1 posted Editorial decision: Revision requested 29 Oct, 2025 Reviews received at journal 27 Oct, 2025 Reviewers agreed at journal 23 Oct, 2025 Reviewers agreed at journal 23 Oct, 2025 Reviews received at journal 21 Oct, 2025 Reviewers agreed at journal 21 Oct, 2025 Reviews received at journal 21 Oct, 2025 Reviewers agreed at journal 21 Oct, 2025 Reviews received at journal 21 Oct, 2025 Reviewers agreed at journal 21 Oct, 2025 Reviewers agreed at journal 21 Oct, 2025 Reviewers invited by journal 21 Oct, 2025 Editor invited by journal 30 Sep, 2025 Editor assigned by journal 30 Sep, 2025 Submission checks completed at journal 30 Sep, 2025 First submitted to journal 24 Sep, 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. 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Introduction","content":"\u003cp\u003ePipkin type IV femoral head fracture refers to femoral head fracture associated with posterior dislocation of the hip joint and ipsilateral acetabular fracture \u003csup\u003e[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]\u003c/sup\u003e. Pipkin type IV femoral head fracture is a high-energy injury characterized by its severity and complexity, difficulty in management and high complication rate \u003csup\u003e[\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]\u003c/sup\u003e. Some physicians categorize it as a floating hip injury \u003csup\u003e[\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]\u003c/sup\u003e. There is no consensus on the diagnosis and treatment of Pipkin type IV femoral head fracture. As the most important weight-bearing joint of the human body, the hip joint plays an important role in the upright standing and movement of the human body. Due to its anatomy, complex functions and deep location of the hip joint, it is difficult to carry out \u003cem\u003ein vivo\u003c/em\u003e mechanical studies, and the reliability of animal model experiments is uncertain. Finite element analysis, one key method applied in computer mechanics analysis, is widely applied in bone biomechanics, especially for the mechanical analysis of irregular structures. This study adopted finite element analysis and biomechanics to analyze the injury mechanism of Pipkin type IV femoral head fracture, bone stress and displacement during surgical treatment of internal fixation and verified the results of the finite element analysis with the clinical data of patients with these types of fractures in Xijing Hospital of Air Force Medical University to provide a theoretical basis for clinical decision-making.\u003c/p\u003e"},{"header":"2. Materials \u0026 Methods","content":"\n\u003ch3\u003e1 General data\u003c/h3\u003e\n\u003cp\u003eIn total, 15 patients with Pipkin type IV femoral head fractures treated at Xijing Hospital from March 2013 to April 2019 were involved in this study, including 11 men and 4 women. They were 27\u0026ndash;70 years, mean 50.6 years. There were 7 cases of car accident injuries, 4 cases of fall injuries and 4 cases of other types. The inclusion criteria were as follows: (1) diagnostic criteria for Pipkin type IV femoral head fracture and (2) surgical treatment. The exclusion criteria were as follows: (1) patients with pathological fractures or patients who underwent conservative treatment; and (2) patients who were lost to follow-up.\u003c/p\u003e\u003cp\u003e\u003cb\u003e2. Methods\u003c/b\u003e\u003c/p\u003e\u003cp\u003e1. The normal hip joint model and Pipkin type IV fracture femoral head model were established, and finite element analysis was used to simulate the stress distribution and displacement of each model.\u003c/p\u003e\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e1.1 Establishment of the three dimensional solid models\u003c/h2\u003e\u003cp\u003eThe CT images of healthy volunteers were imported into Mimics software(Fig.\u0026nbsp;1a), and the tissues were segmented into two-dimensional images to obtain the solid model of each bone and then imported into GeomagicStudio 2015 for smoothing. The STP file was exported last (Fig.\u0026nbsp;1b).\u003c/p\u003e\u003cp\u003eThe STP file was imported into the UG10.0 software. The articular cartilage, fracture model and internal plants were designed according to the requirements, and then the STP files of each model were exported.(Fig.\u0026nbsp;1c and Fig.\u0026nbsp;1d)\u003c/p\u003e\u003cp\u003eThe STP file was imported into hypermesh14.0 software to mesh the model, and finite element models of the nondestructive hip joint (Fig.\u0026nbsp;2a), posterior wall fracture of the acetabulum, femoral head fracture, and Pipkin type IV femoral head fracture were obtained (Fig.\u0026nbsp;2b). The total number of nodes and units in each model was showed in Table\u0026nbsp;1(a).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e1.3 Material property assignment\u003c/h2\u003e\u003cp\u003eEach element in the mesh should be assigned material properties, including the bone, cartilage, and internal fixators. To verify the results, the properties of the mechanical materials were set according to the previous literature. The elastic modulus of the cortical bone material was uniformly set to 10000 MPa, with a Poisson's ratio of 0.29 and cancellous bone of 100 MPa, with a Poisson's ratio of 0.29. Articular cartilage was defined as a linear elastic material, with an elastic modulus of 12 MPa and a Poisson\u0026rsquo;s ratio of 0.4. The material of the prosthetic implant was TC4, with an elastic modulus of 110000 MPa and a Poisson\u0026rsquo;s ratio of 0.3 (Table\u0026nbsp;1(b)).\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e1.4 Boundary settings\u003c/h2\u003e\u003cp\u003eThe boundary conditions were defined as follows: hard sliding contact was defined between the fracture blocks and between the steel plate and bones; bound contact constraints were defined between the screws and bone and between the screws and plate and between the acetabular cortical bone and cartilage; and sliding contact was defined between the femoral head and acetabular cartilage. Contact property: frictional contact; friction coefficient\u0026thinsp;=\u0026thinsp;0.01; calculation: penalty function method.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec7\" class=\"Section2\"\u003e\u003ch2\u003e1.5 Loading\u003c/h2\u003e\u003cp\u003eThe pubic symphysis was fixed without displacement or rotation in any direction (U1\u0026thinsp;=\u0026thinsp;U2\u0026thinsp;=\u0026thinsp;U3\u0026thinsp;=\u0026thinsp;UR1\u0026thinsp;=\u0026thinsp;UR2\u0026thinsp;=\u0026thinsp;UR3\u0026thinsp;=\u0026thinsp;0), and the auricular surface of the sacroiliac joint was constrained (U1\u0026thinsp;=\u0026thinsp;U2\u0026thinsp;=\u0026thinsp;U3\u0026thinsp;=\u0026thinsp;UR1\u0026thinsp;=\u0026thinsp;UR2\u0026thinsp;=\u0026thinsp;UR3\u0026thinsp;=\u0026thinsp;0). In the upright position, 350 N, 550 N, 750 N, 950 N, and 1500 N loads were applied along the femoral axis; at 10\u0026deg; internal rotation, a load of 750 N was applied along the femoral axis in 90\u0026deg; and 120\u0026deg; flexion.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec8\" class=\"Section2\"\u003e\u003ch2\u003e1.6 Finite element analysis\u003c/h2\u003e\u003cp\u003eIn the model of the normal hip joint, different loads were applied in the upright position to simulate the situation in which the lower limbs hit the ground after falling from a height(Fig.\u0026nbsp;3a), and a load was applied at different angles in flexion to simulate the damage of the dashboard in a car accident (Fig.\u0026nbsp;3b).\u003c/p\u003e\u003cp\u003eWhen the normal hip joint model is loaded in the upright position, the stress is concentrated on the longitudinal axis of the iliac bone, the anterior wall of the acetabulum, the top and posterior wall of the acetabulum, the suprapubic branch, the weight-bearing area of the femoral head, the pressure side of the femoral neck, and the femoral distance. The femoral head bears the largest stress, followed by the posterior wall and the top of the acetabulum. The displacement was mainly distributed on the anterior column of the acetabulum, the anterior wall of the acetabulum, the top, posterior wall and posterior column of the acetabulum, the weight-bearing area of the femoral head, the femoral neck, and the intertrochanteric area (Fig.\u0026nbsp;3c). This suggests that Pipkin type IV femoral head fractures are prone to occur when the lower limbs hit the ground after falling from a height.\u003c/p\u003e\u003cp\u003eWhen a load is applied to the normal hip joint model in flexion, the stress is concentrated on the top and posterior wall of the acetabulum and the femoral neck; the displacement is mainly distributed on the posterior wall of the acetabulum and the intertrochanteric area (Fig.\u0026nbsp;3d), which indicates that the patient is prone to a Pipkin type IV femoral head fracture if the dashboard is damaged in a car accident.\u003c/p\u003e\u003cp\u003eWe carried out a classification and comparison of Pipkin type IV femoral head fracture models: all femoral head fractures were fixed with double-head compression screws, and the acetabular fractures were fixed with three different methods: lag screws combined with reconstruction plates, reconstruction plates alone, and lag screws alone. Different loads were applied in the upright position of the joint to simulate the situation in the standing position, and loads at different angles were applied in flexion to simulate the situation during walking.\u003c/p\u003e\u003cp\u003eIn the model of Pipkin type IV femoral head fracture under a load of 750 N in the upright position, when the acetabular fracture was fixed using a combination of lag screws and reconstruction plates, the stress values were 50.73 MPa with a displacement of 0.059 mm in the ilium, and 30.58 MPa with a displacement of 0.284 mm in the femur (Fig.\u0026nbsp;4a\u0026ndash;4d, Fig.\u0026nbsp;7a, Table\u0026nbsp;2c). When fixation was performed with reconstruction plates alone, the stress reached 77.16 MPa with a displacement of 0.175 mm in the ilium, and 74.30 MPa with a displacement of 0.785 mm in the femur (Fig.\u0026nbsp;6a\u0026ndash;6c, Table\u0026nbsp;3a). With lag screws alone, the stress was 87.69 MPa and displacement was 0.187 mm in the ilium, while in the femur the values were 54.74 MPa and 0.689 mm, respectively (Fig.\u0026nbsp;6a\u0026ndash;6c, Table\u0026nbsp;3b).\u003c/p\u003e\u003cp\u003eUnder an increased load of 1500 N in the upright position, fixation with both lag screws and reconstruction plates resulted in a stress of 50.44 MPa and displacement of 0.355 mm in the ilium, and 55.4 MPa with 0.638 mm displacement in the femur (Fig.\u0026nbsp;4a\u0026ndash;4d, Table\u0026nbsp;2b). When only reconstruction plates were used, the stress was 85.08 MPa with 0.849 mm displacement in the ilium, and 146.1 MPa with 1.562 mm displacement in the femur (Fig.\u0026nbsp;6a\u0026ndash;6c, Table\u0026nbsp;6). With lag screws alone, the ilium showed a stress of 141.7 MPa and displacement of 0.875 mm, while the femur exhibited 87.14 MPa and 0.957 mm displacement (Fig.\u0026nbsp;5a\u0026ndash;5d, Table\u0026nbsp;3b).\u003c/p\u003e\u003cp\u003eThese results indicate that the model with acetabular fracture fixed using a combination of lag screws and reconstruction plates exhibited the lowest stress and displacement under varying load conditions (Fig.\u0026nbsp;7). A consistent trend was observed under other load levels of 350 N, 550 N, and 950 N (Table\u0026nbsp;2a\u0026ndash;2c). In summary, for the fixation of acetabular fractures, the combined use of lag screws and reconstruction plates provides superior biomechanical stability compared to the use of either reconstruction plates or lag screws alone.\u003c/p\u003e\u003cp\u003eFor the model of the Pipkin IV femoral head fracture under a load of 750 N in flexion, taking Q30\u0026deg; flexion for example, if the acetabular fracture was fixed with lag screws and reconstruction plates, the stress was 81.93 mpa and the displacement was 0.202 mm in the ilium, 62.09 mpa and 4.621 mm in the femur; if the acetabular fracture was fixed with reconstruction plates, the stress was 144.9 mpa and the displacement was 0.465 mm in the ilium, 96.51 mpa and 7.992 mm in the femur; if the acetabular fracture was fixed with lag screws, the stress was 364.3 mpa and the displacement was 0.505 mm in the ilium, 87.60 mpa and 7.887 mm in the femur (Fig.\u0026nbsp;7, Table\u0026nbsp;3). The overall trend of bone stress and displacement data in the finite element analysis was consistent with that in the upright position (Fig.\u0026nbsp;7), suggesting that fixation with lag screws and reconstruction plates was the most effective for acetabular fractures.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e\n\u003ch3\u003e2 Case collection and follow-up\u003c/h3\u003e\n\u003cp\u003e In accordance with the diagnostic criteria of Pipkin type IV femoral head fracture and the inclusion and exclusion criteria of this study, 15 cases were collected from the Keep running scientific research management system and the quality control system of electronic medical records. All patients were followed up by telephone, WeChat or other contact methods. Some patients were followed up by regular visits in the outpatient clinic, and some patients were followed up at home. During the follow-up, patients were checked by X-rays to observe fracture healing, photos or videos were taken to observe postoperative functional recovery, and the Majeed standard functional scoring system was used to evaluate the hip joint function and quantify functional recovery.\u003c/p\u003e"},{"header":"3. Results","content":"\u003cp\u003eFinite element analysis results\u003c/p\u003e\u003cp\u003eWhen a load is applied to the normal hip joint model in the upright position, the stress is concentrated on the longitudinal axis of the ilium, the anterior wall of the acetabulum, the top and posterior wall of the acetabulum, the suprapubic branch, the weight-bearing area of the femoral head, the pressure side of the femoral neck, and the femoral distance. The femoral head and neck bear the largest stress, followed by the posterior wall and top of the acetabulum; the displacement is mainly distributed on the anterior column of the acetabulum, the anterior wall of the acetabulum, the top, posterior wall and posterior column of the acetabulum, the weight-bearing area of the femoral head, the femoral neck, and the intertrochanteric area. The anterior column of the acetabulum has the largest displacement, followed by the femoral head and neck. This suggests that Pipkin type IV femoral head fractures are prone to occur when the lower limbs hit the ground after falling from height. When a load is applied to the normal hip joint model in 90\u0026deg;, 120\u0026deg; flexion and 10\u0026deg; internal rotation, the stress is concentrated on the top and posterior wall of the acetabulum and the femoral head and neck; the displacement is mainly distributed along the posterior column and posterior wall of the acetabulum, which indicates that the patient is prone to a Pipkin type IV femoral head fracture if the dashboard is damaged in a car accident.\u003c/p\u003e\u003cp\u003eIn a model of Pipkin type IV femoral head fracture, the femoral head is fixed with double-head compression screws, and acetabular fractures are fixed with lag screws and reconstruction plates, resulting in the smallest stress and displacement, which suggests that this method of internal fixation is the most reliable.\u003c/p\u003e\u003cp\u003eClinical follow-up results\u003c/p\u003e\u003cp\u003eA total of 15 patients were followed up for 12\u0026ndash;86 months, with a mean of 34.4 months. There were 7 cases of traffic accident injuries, 4 cases of falling injuries, and 4 cases of other types. Majeed functional scoring was performed to evaluate the hip joint at the last follow-up: 15 cases of femoral head fractures were fixed with double-head compression screws. Among them, 5 cases of acetabular fracture were fixed with lag screws and reconstruction plates, and their hip joint function was graded excellent; 5 cases of acetabular fracture were fixed with reconstruction plates, and their hip joint function was graded good; another 5 cases of acetabular fractures were fixed with lag screws, and their hip joint function was graded good.\u003c/p\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eThe results of finite element analysis in the normal hip joint model are consistent with clinical data in patients with injuries caused by falling from a height and car accidents. The results of the finite element analysis in the model of Pipkin type IV femoral head fracture with internal fixation were consistent with hip function scores in the clinical evaluation. In conclusion, finite element analysis can provide a theoretical basis for exploring the injury mechanism of Pipkin type IV femoral head fractures and provide data support for selecting the optimal internal fixation method, which is beneficial for the clinical diagnosis and treatment of Pipkin type IV femoral head fractures.\u003c/p\u003e"},{"header":"5. Discussion","content":"\u003cp\u003e1. Development of finite element analysis\u003c/p\u003e\u003cp\u003eFinite element analysis (FEA) \u003csup\u003e[\u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/sup\u003e refers to the application of the matrix method in structural mechanics and elastic mechanics. Brekelmans et al. \u003csup\u003e[\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]\u003c/sup\u003e first applied the finite element method in orthopedics in 1972. At present, finite element analysis has been used in bone stress analysis, fixator selection, optimal design and the working life prediction of joint prostheses. In particular, it is mostly applied in the biomechanics of the spine \u003csup\u003e[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e, including detecting pressure changes during joint motion within the spine, selecting materials for spinal internal fixation and surgical methods, and bone stress analysis of the limbs\u003csup\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e (the ankle joint, knee joint, elbow, etc.). Moreover, it is also involved in studies on the pathological mechanism of certain diseases, e.g., plantar stress distribution in diabetic foot patients \u003csup\u003e[\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]\u003c/sup\u003e and the design of artificial joint prostheses, e.g., hip replacement prostheses \u003csup\u003e[\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\u003cp\u003eFinite element analysis has achieved a leap from two-dimensional to three-dimensional. With the development of computer technology and accurate analysis programs, finite element analysis is not confined to simple stress analysis. The combination of the finite element method and digital technology makes the establishment of models more accurate and convenient. Thanks to the advances in biomechanics and computer software, finite element analysis has great potential for applications in orthopedic biomechanics, especially for studies on the pathogenesis of degenerative diseases \u003csup\u003e[\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e]\u003c/sup\u003e and the development and selection of internal or external fixation materials \u003csup\u003e[\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e\n\u003ch3\u003e2. Floating hip injury and Pipkin type IV femoral head fracture\u003c/h3\u003e\n\u003cp\u003eFloating hip injury (FHI) was first proposed by Liebergall et al.\u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e and was defined as an unstable pelvic fracture or acetabular fracture caused by high-energy violence accompanied by an ipsilateral femoral fracture \u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e. Based on Tile\u0026rsquo;s classification of pelvic fractures \u003csup\u003e[\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e]\u003c/sup\u003e, Liebergall et al.\u003csup\u003e[\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]\u003c/sup\u003e divided floating hip injuries into 3 types. Muller\u0026rsquo;s classification is also commonly applied in the clinic \u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e. Muller\u0026rsquo;s classification and Liebergall\u0026rsquo;s classification are widely used in clinical practice, but neither has evaluated the subdivision of femoral fractures. Floating hip injury is a kind of floating joint injury that refers to extra-articular or intra-articular fracture of the upper and lower bones adjacent to the joint \u003csup\u003e[\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e]\u003c/sup\u003e. Accordingly, femoral fractures in floating hip injuries can be subdivided into proximal femoral fractures, femoral shaft fractures, and distal femoral fractures. Because of the involvement of hip joints, those with acetabular fractures or femoral head fractures can be regarded as intra-articular floating hip injuries, among which Pipkin type IV femoral head fracture (i.e., acetabular fracture) combined with ipsilateral femoral head fracture and dislocation is the most severe in the clinic. Pipkin type IV femoral head fracture has a lot in common with floating hip injury, including the injury mechanism, cause of violence, treatment principles and complications; therefore, it is considered one type of floating hip injury. An epidemiological survey on floating hip injury by Zhang et al. \u003csup\u003e[\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e]\u003c/sup\u003e revealed that the most common type of floating hip injury is the Muller A type \u003csup\u003e[\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]\u003c/sup\u003e, and floating hip injuries with proximal fractures of the ipsilateral acetabulum and femoral head are the most common in the clinic. In other words, the Pipkin type IV femoral head fracture is the most common type of floating hip injury. In this study, we established a finite element model of Pipkin type IV femoral head fracture with internal fixation and performed a mechanical analysis, which was of clinical significance for the treatment of floating hip injuries.\u003c/p\u003e\n\u003ch3\u003e3. Application of finite element analysis of Pipkin type IV femoral head fractures\u003c/h3\u003e\n\u003cp\u003eIf the hip joint is seriously traumatized, it is prone to severe consequences, such as femoral head necrosis or traumatic arthritis \u003csup\u003e[\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]\u003c/sup\u003e. Due to the limited source of the specimens and the difficulty in controlling the experimental conditions, biomechanics experiments on hip joints are restricted \u003csup\u003e[\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]\u003c/sup\u003e. Finite element analysis has good adaptability to the complex structure of the hip joint. It can simulate many clinical conditions by changing the parameters and analyze the mechanical changes of the hip joint in the physiological and pathological processes \u003csup\u003e[\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]\u003c/sup\u003e. Most femoral head fractures are caused by high-energy injuries. The surgery is difficult and demanding, and choosing an appropriate fixation method is a key step to ensure its efficacy \u003csup\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/sup\u003e. In view of the complexity and severity of Pipkin type IV femoral head fracture, there is no strong evidence about its treatment or quality evaluation, especially for the effect of internal fixation on postoperative joint function. Finite element analysis can play an irreplaceable role in the diagnosis and treatment of Pipkin type IV femoral head fractures.\u003c/p\u003e\n\u003ch3\u003e4. Precautions for the application of finite element analysis\u003c/h3\u003e\n\u003cp\u003eThe purpose of finite element analysis is to provide a biomechanical and theoretical basis for clinical applications. Existing modeling methods cannot achieve an absolute real simulation. Therefore, accurate modeling is the primary prerequisite to ensure the authenticity and reliability of simulation data. In addition, human errors in load and boundary condition settings, cell division, node selection, and elastic modulus settings can also affect the authenticity and reliability of the research data, which requires a rigorous scientific attitude and the meticulousness of researchers, as well as careful planning and arrangement. Finite element analysis requires pure theoretical research. The results of theoretical research are generally based on tendencies and qualitative perspectives. We need to minimize human errors and improve the reliability of research data and at the same time, the results of finite element analysis need to be compared, verified and comprehensively analyzed with \u003cem\u003ein vivo\u003c/em\u003e or \u003cem\u003ein vitro\u003c/em\u003e experiments, animal experiments and clinical observations to ensure the conscientiousness and reliability of the scientific research \u003csup\u003e[\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]\u003c/sup\u003e. In this study, the results of finite element analysis of related models were confirmed by clinical follow-up data of patients with Pipkin type IV femoral head fractures, so the conclusion is reliable.\u003c/p\u003e\n\u003ch3\u003e5. Disadvantages and prospects of the finite element analysis\u003c/h3\u003e\n\u003cp\u003eFinite element analysis can fully control the experimental conditions and simulate the biomechanical experiments to the greatest extent by computers, which play a bridging role in the transitional stage from animal experiments to clinical human specimen experiments \u003csup\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e. However, finite element analysis also shows the following disadvantages \u003csup\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]\u003c/sup\u003e: (1) finite element technology belongs to engineering mechanics, and its calculation requires a strong capability of mathematical logic and reasoning, which hampers its application; (2) in cases of Pipkin type IV femoral head fractures, the shape of the femoral head and acetabulum is irregular, so it is difficult to accurately simulate internal stress distribution with an elastic modulus of finite element cells. Both the experimental data and approximation can affect the accuracy; (3) the motion system of the human body is both dynamic and static, e.g., the hip joint has a three-dimensional axis of movement, undertaking a complex range of motion, such as external rotation, external abduction, internal rotation, adduction, flexion and extension \u003csup\u003e[\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]\u003c/sup\u003e. The mechanism of Pipkin type IV femoral head fracture and postoperative functional recovery should be investigated during the state of motion, and only in this way can the results be more realistic. Finite element analysis is insufficient in studying the stress distribution and displacement of the bone and joint in motion, which is the direction of future studies \u003csup\u003e[\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]\u003c/sup\u003e.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eAcknowledgments\u003c/p\u003e\n\u003cp\u003eNone\u003c/p\u003e\n\u003cp\u003eAuthor contributions\u003c/p\u003e\n\u003cp\u003eAll authors participated in the conception and design of this study.Yefan Zhang,Jiahao Zeng , and Mwnglong Wang contributed to data collection and analysis. Yefan Zhang writed the first draft of the manuscript. Qiyou Cao, along with Haifeng Dang, Long Bi, Zhuojing Luo, completed the design and correction of the chart. Junjun Fan, Donglin Li and Haifeng Dang revised the manuscript. All authors read and agreed to the final manuscript.\u003c/p\u003e\n\u003cp\u003eFunding\u003c/p\u003e\n\u003cp\u003eNone\u003c/p\u003e\n\u003cp\u003eEthics approval and consent to participate\u003c/p\u003e\n\u003cp\u003eThe study was approved by the Ethics Committee of \u0026nbsp; Xijing Hospital of Military Medical University (approval No. QX20221008-1), and the need for informed consent was waived by the ethics committee. All procedures involving human participants in this study were conducted in accordance with the principles of the Declaration of Helsinki.\u003c/p\u003e\n\u003cp\u003eClinical trial number\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003eConsent for publication\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003eCompeting interests\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests\u003c/p\u003e\n\u003cp\u003eAuthor details\u003c/p\u003e\n\u003cp\u003e1Department of Orthopedics, Xijing Hospital of Military Medical University (Xi \u0026apos;an, 710032),China . \u0026nbsp; Email:fanjunjunys＠163.com \u0026nbsp; [email protected]\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003ePipkin G. Treatment of grade IV fracture-dislocation of the hip[J]. 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The floating hip\u0026ndash;ipsilateral pelvic and femoral fractures[J]. JBJS. 1992;74\u0026ndash;B:93\u0026ndash;100.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eM\u0026uuml;ller EJ, Siebenrock K, Ekkernkamp A, et al. Ipsilateral fractures of the pelvis and the femur \u0026ndash; floating hip? A retrospective analysis of 42 cases[J]. Arch Orthop Trauma Surg. 1999;119:179\u0026ndash;82.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eTile M. Pelvic ring fractures: should they be fixed?[J]. J bone joint Surg Br volume. 1988;70(1):1\u0026ndash;12.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eLiebergall M, Mosheiff R, Safran O, et al. The floating hip injury: patterns of injury[J]. Injury. Int J Care Injured. 2002;33:717\u0026ndash;22.\u003c/span\u003e\u003c/li\u003e\u003cli\u003e\u003cspan\u003eJi Chenni L, Shilun Z, Yingze, et al. Epidemiological survey of adult floating hip fractures in 83 hospitals from 2010 to 2011 [J]. 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Mater Design. 2007;28(5):1577\u0026ndash;83. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1016/j.matdes.2006.02.015\u003c/span\u003e\u003cspan address=\"10.1016/j.matdes.2006.02.015\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003eTables 1 to 3 are available in the Supplementary Files section.\u003c/p\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":"bmc-musculoskeletal-disorders","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmsd","sideBox":"Learn more about [BMC Musculoskeletal Disorders](http://bmcmusculoskeletdisord.biomedcentral.com/)","snPcode":"","submissionUrl":"https://author-welcome.nature.com/12891","title":"BMC Musculoskeletal Disorders","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"finite element analysis, femoral head fracture, Pipkin type IV, diagnosis, treatment","lastPublishedDoi":"10.21203/rs.3.rs-7703193/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7703193/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e\u003cstrong\u003eObjective \u003c/strong\u003eTo investigate the application value of finite element analysis in the diagnosis and treatment of Pipkin type IV femoral head fractures.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMethods\u003c/strong\u003e Finite element models of normal hip joints and Pipkin type IV femoral head fractures were separately established, and the stress distribution and displacement of each model were simulated using finite element analysis. Clinical data were retrospectively collected from 15 patients with Pipkin type IV femoral head fractures who underwent surgical treatment at Xijing Hospital, Air Force Medical University, between March 2013 and April 2019. Their hip joint function was evaluated during follow-up, and the findings from the finite element analysis were validated through comparison with the clinical follow-up results.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eResults\u003c/strong\u003e The results of the finite element analysis were as follows: (1) When a load is applied to the normal hip joint model in the upright position, the femoral head bears the largest stress, followed by the posterior wall and top of the acetabulum, and the anterior column of the acetabulum experiences the largest displacement, followed by the femoral neck, which suggests that Pipkin type IV femoral head fractures are prone to occur when the lower limbs hit the ground after falling from a height. When a load is applied to the normal hip joint model in 90°, 120° flexion and 10° internal rotation, the stress is concentrated on the top and posterior wall of the acetabulum and the femoral neck and the displacement is mainly distributed along the posterior column and posterior wall of the acetabulum, which indicates that the patient is prone to Pipkin type IV femoral head fracture if the dashboard is damaged in a car accident. (2) In the model of Pipkin type IV femoral head fracture, acetabular fractures are fixed with lag screws and reconstruction plates, resulting in the smallest stress and displacement, which suggests that this method of internal fixation is the most reliable. The clinical follow-up results were as follows: a total of 15 patients were followed up for 12–86 months, with a mean of 34.4 months and Majeed functional scoring was performed to evaluate the hip joint at the last follow-up after their femoral head fractures were fixed with double-head compression screws. Among them, 5 cases of acetabular fracture were fixed with lag screws and reconstruction plates, and their hip joint function was graded excellent; 5 cases of acetabular fracture were fixed with reconstruction plates, and their hip joint function was graded good; another 5 cases of acetabular fractures were fixed with lag screws, and their hip joint function was graded as good.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConclusion \u003c/strong\u003eThe results of finite element analysis in the normal hip joint model are consistent with the clinicaldata of patients with injuries caused by falling from a height and car accidents, so finite element analysis can provide evidence for the early diagnosis of Pipkin type IV femoral head fractures. The results of the finite element analysis in the model of Pipkin type IV femoral head fracture with internal fixation are consistent with the hip function scores in the clinical evaluation, so finite element analysis can provide guidance for selecting optimal internal fixation. In short, finite element analysis can play an important role in the clinical diagnosis and treatment of Pipkin type IV femoral head fractures.\u003c/p\u003e","manuscriptTitle":"Diagnosis and treatment of Pipkin type IV femoral head fracture: a finite element analysis","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-10-31 15:27:57","doi":"10.21203/rs.3.rs-7703193/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-10-29T13:05:36+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-27T18:26:26+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"275664448526129526682902106891679221267","date":"2025-10-23T18:40:17+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"2760162200389740410776572017214696200","date":"2025-10-23T16:40:56+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-22T02:14:17+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"193865583858002708630373200510782562794","date":"2025-10-22T01:51:17+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-22T00:42:04+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"74036087994947016174232241896161772698","date":"2025-10-22T00:05:22+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-10-21T13:18:38+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"130169175316140338289576480389986415625","date":"2025-10-21T13:04:24+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"312946453145996983273566941885039410964","date":"2025-10-21T10:55:55+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-10-21T10:38:04+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2025-09-30T13:09:43+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-09-30T06:38:18+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-09-30T06:34:57+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Musculoskeletal Disorders","date":"2025-09-24T11:23:48+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-musculoskeletal-disorders","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"bmsd","sideBox":"Learn more about [BMC Musculoskeletal Disorders](http://bmcmusculoskeletdisord.biomedcentral.com/)","snPcode":"","submissionUrl":"https://author-welcome.nature.com/12891","title":"BMC Musculoskeletal Disorders","twitterHandle":"BMC_series","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"a71f887a-9459-4ea3-bbf9-64c259c37f68","owner":[],"postedDate":"October 31st, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2026-01-12T16:03:43+00:00","versionOfRecord":{"articleIdentity":"rs-7703193","link":"https://doi.org/10.1186/s12891-025-09435-9","journal":{"identity":"bmc-musculoskeletal-disorders","isVorOnly":false,"title":"BMC Musculoskeletal Disorders"},"publishedOn":"2026-01-07 15:58:07","publishedOnDateReadable":"January 7th, 2026"},"versionCreatedAt":"2025-10-31 15:27:57","video":"","vorDoi":"10.1186/s12891-025-09435-9","vorDoiUrl":"https://doi.org/10.1186/s12891-025-09435-9","workflowStages":[]},"version":"v1","identity":"rs-7703193","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7703193","identity":"rs-7703193","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}