Impact of Age-Related Decline in Bone Mineral Density on Internal Fixation for Nondisplaced Femoral Neck Fractures: A Finite Element Analysis Using Virtual Simulation Models

Impact of Age-Related Decline in Bone Mineral Density on Internal Fixation for Nondisplaced Femoral Neck Fractures: A Finite Element Analysis Using Virtual Simulation Models | 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 Impact of Age-Related Decline in Bone Mineral Density on Internal Fixation for Nondisplaced Femoral Neck Fractures: A Finite Element Analysis Using Virtual Simulation Models Sakura Kuniyoshi, Satoshi Nakasone, Mika Takaesu, Fumiyuki Washizaki, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9411724/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 7 You are reading this latest preprint version Abstract Background As the global population ages, the incidence of femoral neck fractures (FNFs) is rising. While internal fixation is generally preferred for nondisplaced FNFs, clinical outcomes in elderly patients remain controversial due to high complication rates associated with osteoporosis. This study aimed to establish a novel finite element analysis (FEA)-based evaluation method using virtual models to isolate the independent biomechanical effect of age-related, region-specific decline in bone mineral density (BMD) on the stability of internal fixation for nondisplaced FNFs. Methods A 70° Pauwels angle nondisplaced FNF model was created using CT data from a 30-year-old woman and was fixed with a fixed angle device. Eight virtual femur models, simulating ages 30 to 100, were generated by adjusting regional volume-BMD (vBMD) based on established longitudinal aging data. Linear FEA was performed to simulate single-leg standing. Evaluation parameters included mean von Mises stress (VMS) on screws, the fracture risk index (FRI) of the surrounding cancellous bone, and the relative displacement of the fracture fragments. Results Increasing simulated model age was associated with progressive decrease in regional vBMD across all areas. This decline led to a concomitant increase in mean implant VMS and the FRI of the bone surrounding the screws, particularly in load-bearing regions and around screw threads. Between simulated ages 30 and 80, the FRI increased by 101% to 125% across the three screws, with the distal screw showing the greatest increase. Furthermore, fracture fragment displacement increased with advancing model age, indicating reduced construct stiffness. Conclusions Age-related reduction in vBMD alone significantly compromises the biomechanical stability of internal fixation in nondisplaced FNFs, even when fracture morphology and implant configuration are identical. These findings suggest that BMD assessment is essential for surgical planning; in cases of severe osteoporosis, surgeons may need to consider alternative strategies, such as arthroplasty, despite the absence of fracture displacement. Bone mineral density Finite element analysis Nondisplaced femoral neck fracture Osteoporosis Virtual model Pauwels Type III Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Background As the global population ages, the prevalence of osteoporosis increases, resulting in a growing incidence of hip fractures, including femoral neck fractures (FNFs), with the total number of cases projected to reach approximately 6 million worldwide by 2050 [1, 2]. The conventional treatment strategies for FNFs are generally determined according to the Garden classification [3], which divides FNFs into four types based on displacement and fracture completeness and guides treatment decisions. Preservation of the femoral head is generally favored for Garden stages 1 and 2 (incomplete or complete nondisplaced fractures), whereas arthroplasty is indicated for Garden stages 3 and 4 (displaced fractures) [4]. However, in elderly patients, the optimal treatment strategy for nondisplaced FNFs remains controversial, as outcomes following osteosynthesis have been reported to be unsatisfactory in this population [5–7]. Osteoporosis associated with aging disrupts the balance of bone resorption and formation, resulting in decreased bone mineral density (BMD), and impaired bone quality and microarchitecture [8]. Previous clinical studies have reported high rates of internal-fixation-related complications in elderly patients with nondisplaced hip fractures due to osteoporosis, including osteonecrosis, nonunion, implant-related complications, and persistent pain [6, 9, 10]. This is partly because traditional fixation methods, originally designed for healthy bone, may fail to provide sufficient stability in osteoporotic bone [8]. However, clinical studies evaluating internal fixation in osteoporotic femoral neck fractures are often affected by heterogeneity in femoral morphology, fracture patterns, and patient characteristics, making it difficult to isolate the specific biomechanical contribution of osteoporosis. Meanwhile, finite element analysis (FEA) has been introduced into the field of orthopedic surgery, enabling detailed biomechanical analysis of bone-implant constructs [11]. Using FEA, previous studies have investigated optimal internal fixation strategies for nondisplaced FNFs from perspectives such as implant type [12–14], screw insertion angle [15, 16], and Pauwels angle [17–21]. However, to the best of our knowledge, no previous study has specifically isolated the independent biomechanical effect of osteoporotic bone changes on fixation stability in nondisplaced FNFs. This study focused specifically on age-related, region-specific decline in BMD. The objectives were: (1) to establish a novel FEA-based evaluation method using virtual models that incorporate age-related BMD reduction; and (2) to elucidate the relationship between BMD and the mechanical stability of internal fixation for nondisplaced FNFs. Materials and methods Study design and setting This retrospective study was approved by the International Review Board of Graduate School of Medicine, University of the Ryukyus (#23-2188, Oct. 18th 2023). All procedures were performed in accordance with the principles of the Declaration of Helsinki. Informed consent was obtained by optout process. A healthy 30-year-old woman without a history of osteoporosis or fragility fracture with available pelvic computed tomography (CT) scan data was used for analysis. Preoperative data were obtained using 160-row spiral CT (Aquilion Precision, Canon Medical Systems Inc., Tochigi, Japan). Data with a 0.5-mm thickness were saved in Digital Imaging and Communications in Medicine format and were imported into quantitative CT/FEA software (MECHANICAL FINDER ver. 13, Research Center of Computational Mechanics, Inc., Tokyo, Japan). Modeling First, a horizontal line was created perpendicular to the proximal shaft axis of the femur. The fracture plane was then created and set at an angle of 70° to the horizontal line, creating a nondisplaced FNF model with a Pauwels angle of 70° (Fig. 1 ). In our previous study, we demonstrated that the angular stability provided by a fixed angle device (FAD) is essential for resisting shear forces in Pauwels 70° FNFs [17]; therefore, the Prima Hip Screw Side Plate System (PHS + SP, Ortho Development Corporation, UT, USA) was selected as the internal fixation device in the present study. To create an ideal model of FAD fixation, all screw lengths were sufficient such that the screw tips were located within 3 mm of subchondral bone [22], the distal screw was positioned adjacent to the inner inferior cortex of the femoral neck, and the femoral plate was set parallel to the femoral shaft (Fig. 2 ). Meshing Mesh generation was performed using the extracted CT images of the femur and the stereolithographic data of the PHS + SP. The general element size was set to 2 mm. To allow region-specific adjustments of BMD, the femur was subdivided into five anatomical regions, including the femoral head, femoral neck, greater trochanter, intertrochanteric region, and femoral shaft (Fig. 3 ). The model consisted of 202,859 nodes and 893,379 elements. The mesh convergence test was conducted to validate this mesh size setting. Material properties and creating virtual models In the quantitative CT/FEA software used in this study, volume-BMD (vBMD) is calculated from the Hounsfield unit (HU) of the imported CT images using a proprietary calibration curve and the conversion formula described below: $$\:vBMD\:\left(\frac{g}{c{m}^{3}}\right)=\:\frac{\left\{\left(HU\:+\:1.42\right)0.001\right\}}{1.058}$$ The obtained BMD is then substituted into Keyak’s conversion equation to calculate the Young’s modulus [23]. Using the quantitative annual evolution of regional femoral BMD reported by Dudle et al. [24] (Table 1 ), together with the aforementioned conversion formula, the integrated vBMD values were estimated at 10, 20, 30, 40, 50, 60, and 70 years in the future for each of the five regions. These values were then assigned to the corresponding regions as material properties to modify the original femur model, thereby generating eight virtual femur models simulating progressive aging. A Poisson’s ratio of 0.4 was set for the femur. For the titanium alloy, a Young’s modulus of 108,000 MPa and a Poisson’s ratio of 0.28 were assigned to PHS + SP [25]. Table 1 Quantitative annual change in regional femoral BMD reported by Dudle et al. [24] Femoral head Femoral neck Greater trochanter Intertrochanteric region Femoral shaft Annual change in BMD (%) –0.54 –0.68 –0.48 –0.75 –0.44 BMD, bone mineral density. Contact conditions Based on previous studies, the friction coefficients for the bone–bone and bone–screw interfaces were 0.46 and 0.42, respectively. To recreate the barrel mechanism of the PHS + SP, the screws were divided into outer and inner parts and were assigned frictional contact, with a friction coefficient of 0.2 [26]. The femoral plate/outer part of the PHS and the femoral plate/bone interfaces were assumed to be fixed. Boundary conditions To simulate the single-leg standing position, the model was abducted 10° and tilted backward by 9° [27]. A downward force of three times the body weight (1500 N) was applied to the surface of the femoral head [12] (Fig. 4 ). The distal end of the femur was embedded in a soft material (Young’s modulus = 0.2, Poisson’s ratio = 0.3) to prevent excessive stress around the fixed area, and the material was fixed in all directions [28]. Evaluation Linear analysis was conducted. The mean von Mises stress (VMS) of the three screws of the PHS + SP was evaluated individually. To evaluate the stability of the screws, a region of interest (ROI) was defined in the bone surrounding the screws, and mean fracture risk index (FRI) [29] of the ROI was compared between the two models. The FRI is defined as the ratio of the VMS to yield stress, averaged over the ROI, with a higher FRI indicating an increased likelihood of element failure and a greater risk of screw loosening. For fracture stability, the average relative displacement of the fracture surface was evaluated as the amount of fracture fragment displacement. Results Table 2 summarizes the estimated integrated vBMD values for each femoral region in the original model and at simulated aging stages from 10 to 70 years. A gradual decrease in vBMD was observed across all femoral regions with increasing simulated age. Table 2 Estimated integral volume bone mineral density for each femoral region in age-specific virtual models Femoral region Model age (years) 30 40 50 60 70 80 90 100 Femoral head 251 238 225 213 202 191 181 172 Femoral neck 454 424 396 370 346 323 302 282 Greater trochanter 378 360 343 327 312 297 283 270 Intertrochanteric region 309 287 266 247 229 212 197 183 Femoral shaft 600 574 549 526 503 481 461 441 All values of bone mineral density are provided in mg/cm 3 . Increasing model age was associated with higher mean implant VMS values (Fig. 5 ). Consistently, the mean FRI values of the cancellous bone surrounding the screws also increased with age (Fig. 6 ). Contour plots demonstrated a marked increase in FRI, particularly in load-bearing regions, fracture sites, and around the screw threads (Fig. 7 ). In addition, the relative displacement of fracture fragment increased with advancing model age, accompanied by a concomitant increase in the mean FRI of cancellous bone surrounding the three screws (Fig. 8 ). Discussion To our knowledge, no previous studies have visualized biomechanical changes associated with age-related declines in vBMD during internal fixation for nondisplaced FNF using FEA. The most important finding of the present study is that age-related, region-specific reductions in vBMD alone significantly affect the mechanical stability of internal fixation for nondisplaced FNFs. As model age increased, the VMS of the implant as well as the FRI of the cancellous bone around the screws progressively increased, and fracture fragment displacement became greater. These findings suggest that a decrease in vBMD itself plays a substantial role in fixation instability, even when fracture morphology and implant configuration are identical. Clinical studies have reported unsatisfactory outcomes after internal fixation in elderly patients with nondisplaced FNFs [30]. However, interpretation of these findings is difficult because of confounding factors such as variability in femoral morphology, fracture configuration, implant positioning, and patient-related characteristics. By constructing virtual models in which only vBMD was modified according to age-related regional decline while maintaining other factors constant, the present study isolated the independent biomechanical effect of vBMD reduction. This approach enables a direct mechanical explanation for the higher complication rates observed in elderly patients. The magnitude of vBMD reduction implemented in the present virtual models appears reasonable. A previous study by Gamio et al. reported femoral neck integral vBMD values of 404 mg/cm 3 in 94 young women (mean age, 34 years) and 294 mg/cm 3 in 157 elderly women (mean age, 79 years), all without a history of fragility fractures [31]. Wu et al. assessed femoral neck vBMD in postmenopausal women using quantitative multi-slice CT and reported that the value of integrated femoral neck vBMD was 347.1 mg/cm 3 in the group without osteoporosis or a history of vertebral fracture (mean age, 56.8 years) [32]. The vBMD values of the original model and the virtual models generated in this study were comparable to these reported values, supporting the validity of the present models. For uneventful fracture healing, certain conditions are required of the bone/implant construct, including mechanically sound fixation. Implant fatigue and screw loosening may jeopardize maintenance of fracture healing [33]. Previous studies have demonstrated a strong positive correlation between BMD and elastic modulus at the bulk scale, indicating that reductions in BMD are associated with decreased bone stiffness and yield strength [34, 35]. As the mechanical competence of cancellous bone depends largely on BMD, a reduction in BMD diminishes the bone’s capacity to withstand mechanical loading [4]. As a consequence, stress concentrations increase at the screw-bone interface, particularly in load-bearing regions and screw threads, as reflected by the elevated FRI observed in the present study. Between ages 30 and 80, FRI increased by approximately 31 (125%) in the distal screw, 26 (103%) in the proximal posterior screw, and 23 (101%) in the proximal anterior screw, with the greatest increase observed in the distal screw. Such stress concentrations may promote microdamage accumulation and contribute to progressive screw loosening over time [36]. Furthermore, the increased displacement of the fracture fragments with advancing model age suggests reduced construct stiffness, a condition that is particularly critical in Pauwels 70° fractures where shear forces predominate. A previous investigation has shown that local mechanical quality of the bone, as well as the predicted magnitude of its loading, are important parameters for assessing the loosening risk of the screws [36]. The study mainly focused on pull-out behavior of the screws, in which tensile failure represents the primary failure mode, and therefore used failure strength as the reference parameter. In contrast, in the present study, compressive deformation was considered the dominant mechanical response. Thus, we adopted FRI as a parameter to assess the risk of screw loosening, defined as the ratio of VMS to yield stress of the bone. The yield stress represents the threshold at which bone begins to undergo plastic deformation under compression [23]. From a clinical perspective, surgeons should bear in mind that even in cases with identical fracture displacement or Pauwels angle, differences in bone mineral density may require different treatment strategies. The present study demonstrated that poor bone quality may compromise fixation stability. Therefore, assessment of BMD is essential when selecting the most appropriate patient-specific treatment strategy. In patients with severe osteoporosis, particularly those with steep Pauwels angles, surgeons should not base the decision for internal fixation solely on the absence of fracture displacement. Instead, careful consideration should be given to implant selection and surgical strategy, and alternative approaches such as arthroplasty may be considered [7, 37–40]. The present study had several limitations. It did not incorporate impaired bone quality and microarchitecture, which are also important changes associated with aging. Future models including bone quality deterioration may provide a more comprehensive understanding; nevertheless, isolating the effect of vBMD reduction allowed us to clarify its independent biomechanical contribution to fixation stability. Moreover, the effects of soft tissues, such as muscles and ligaments, were not simulated in our study. Despite these limitations, this study had several strengths. The analysis was based on CT data from an existing case, incorporating the nonlinear material properties of the bone. In addition, region-specific age-related reductions in vBMD were subdivided into five anatomical regions, and a total of eight well-established FEA models were generated to reflect these regional differences. This modeling strategy enabled a more realistic representation of age-related femoral changes. By integrating longitudinal vBMD evolution data into patient-specific FEA models, the present study provides a novel methodological framework that may be applied to other osteoporotic fracture analyses. Conclusions By applying FEA, we successfully developed models that represent region-specific changes in femoral vBMD associated with aging. Using these models, we demonstrated that reductions in vBMD increased the risk of screw loosening and resulted in greater fracture displacement. These findings provide biomechanical evidence supporting the importance of bone quality assessment when selecting surgical strategies for FNFs, especially in elderly patients. Abbreviations FNF Femoral neck fracture BMD Bone mineral density FEA Finite element analysis CT Computed tomography FAD Fixed angle device PHS + SP Prima Hip Screw Side Plate System v-BMD Volume bone mineral density HU Hounsfield unit VMD Von Mises stress ROI Region of interest FRI Fracture risk index Declarations Ethics approval and consent to participate This retrospective study was approved by the International Review Board of Graduate School of Medicine, University of the Ryukyus (#23-2188, Oct. 18th 2023). All procedures were performed in accordance with the principles of the Declaration of Helsinki. Informed consent was obtained by optout process. Consent for publication Not applicable. Competing interests: The authors declare that they have no competing interests. Funding: This study was supported by a Grant in Aid for Scientific Research (C) (General) 2027–2029. Author Contribution SK: Design of this study, Finite element analysis, Drafting. SN: Revising the article for important intellectual content. KO: Advice on model development. MT, FW: Interpretation of the results. KN: Final approval of the version to be submitted. Acknowledgement The authors are grateful to Research Center of Computational Mechanics for their technical advises in using MECHANICAL FINDER ver.13. Data Availability Data is provided within the manuscript. And all data used and analyzed during the current study are available from the corresponding author on reasonable request. References Cauley JA. Public health impact of osteoporosis. Journal of Gerontology Series A: Biological Sciences and Medical Sciences . 2013; 68:1243–1251. Karagas MR, et al. Heterogeneity of hip fracture: age, race, sex, and geographic patterns of femoral neck and trochanteric fractures among the US elderly. American Journal of Epidemiology . 1996; 143:677–682. Garden RS. Low-angle fixation in fractures of the femoral neck. 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Outcomes of elderly patients with nondisplaced or minimally displaced femoral neck fractures treated with internal fixation: a systematic review and meta-analysis. Injury . 2019; 50:2158–2166. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 10 May, 2026 Reviewers agreed at journal 19 Apr, 2026 Reviewers invited by journal 19 Apr, 2026 Editor invited by journal 17 Apr, 2026 Editor assigned by journal 16 Apr, 2026 Submission checks completed at journal 16 Apr, 2026 First submitted to journal 14 Apr, 2026 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. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9411724","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":628377701,"identity":"f162cf9b-a19a-4f46-ae99-0a78d9540db0","order_by":0,"name":"Sakura Kuniyoshi","email":"","orcid":"","institution":"University of the Ryukyus","correspondingAuthor":false,"prefix":"","firstName":"Sakura","middleName":"","lastName":"Kuniyoshi","suffix":""},{"id":628377702,"identity":"025a5650-3fdf-4286-b9e0-b1b131972768","order_by":1,"name":"Satoshi Nakasone","email":"data:image/png;base64,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","orcid":"","institution":"University of the Ryukyus","correspondingAuthor":true,"prefix":"","firstName":"Satoshi","middleName":"","lastName":"Nakasone","suffix":""},{"id":628377703,"identity":"b40e007d-4825-4680-8197-aac959700dad","order_by":2,"name":"Mika Takaesu","email":"","orcid":"","institution":"University of the Ryukyus","correspondingAuthor":false,"prefix":"","firstName":"Mika","middleName":"","lastName":"Takaesu","suffix":""},{"id":628377704,"identity":"aeb4201b-4676-4b2b-95b6-93bdf90737de","order_by":3,"name":"Fumiyuki Washizaki","email":"","orcid":"","institution":"University of the Ryukyus","correspondingAuthor":false,"prefix":"","firstName":"Fumiyuki","middleName":"","lastName":"Washizaki","suffix":""},{"id":628377705,"identity":"473d63fb-eb65-45df-8583-19aa010861b2","order_by":4,"name":"Kenta Otsuki","email":"","orcid":"","institution":"University of the Ryukyus","correspondingAuthor":false,"prefix":"","firstName":"Kenta","middleName":"","lastName":"Otsuki","suffix":""},{"id":628377706,"identity":"30017fc5-e9fb-4af6-8e72-b2d3e15e1caf","order_by":5,"name":"Kotaro Nishida","email":"","orcid":"","institution":"University of the Ryukyus","correspondingAuthor":false,"prefix":"","firstName":"Kotaro","middleName":"","lastName":"Nishida","suffix":""}],"badges":[],"createdAt":"2026-04-14 07:10:56","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9411724/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9411724/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":107965738,"identity":"827fadcb-b631-46ad-95b2-71789c23b5a2","added_by":"auto","created_at":"2026-04-28 05:41:16","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":31806,"visible":true,"origin":"","legend":"\u003cp\u003eGeometric definition of the 70° Pauwels fracture model relative to femoral axis. A horizontal line perpendicular to the proximal shaft axis of the femur was created, and the fracture plane was set at an angle of 70° to this line.\u003c/p\u003e","description":"","filename":"OnlineFig1.png","url":"https://assets-eu.researchsquare.com/files/rs-9411724/v1/89e1b70091f265421978d52f.png"},{"id":107965740,"identity":"ffb8e4e8-b7a2-4290-aaa1-bfd1be01291e","added_by":"auto","created_at":"2026-04-28 05:41:16","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":17389,"visible":true,"origin":"","legend":"\u003cp\u003ePlacement of the internal fixation device. A fixed angle device was selected as the internal fixation device. All screw lengths were sufficient such that the screw tips were located within 3 mm of subchondral bone, and the distal screw was placed close to the inner inferior cortex of the femoral neck. The femoral plate was set parallel to the femoral shaft.\u003c/p\u003e","description":"","filename":"OnlineFig2.png","url":"https://assets-eu.researchsquare.com/files/rs-9411724/v1/3f3ba8d80a0197a86c1f3871.png"},{"id":107965790,"identity":"eda64434-f19b-49b2-966f-257df5dad2b5","added_by":"auto","created_at":"2026-04-28 05:41:30","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":24795,"visible":true,"origin":"","legend":"\u003cp\u003eAnatomical regions of the femur. For the region-specific adjustments of bone mineral density, the femur was subdivided into five anatomical regions, including femoral head, femoral neck, greater trochanter, intertrochanteric region, and femoral shaft.\u003c/p\u003e","description":"","filename":"OnlineFig3.png","url":"https://assets-eu.researchsquare.com/files/rs-9411724/v1/d86ed597f27bfb74b6befd58.png"},{"id":107965739,"identity":"c6cfea05-2ffb-482a-825f-409e11a645b5","added_by":"auto","created_at":"2026-04-28 05:41:16","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":114610,"visible":true,"origin":"","legend":"\u003cp\u003eSimulation position. To simulate the single-leg standing position, the model was abducted 10° and tilted backward by 9°. A downward force of three times the body weight was applied to the surface of the femoral head.\u003c/p\u003e","description":"","filename":"OnlineFig4.png","url":"https://assets-eu.researchsquare.com/files/rs-9411724/v1/c3a905df8b64167ee9dca500.png"},{"id":107965667,"identity":"24867b2a-284e-44a9-a143-ddd3cb06c167","added_by":"auto","created_at":"2026-04-28 05:41:01","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":13698,"visible":true,"origin":"","legend":"\u003cp\u003eMean von Mises stress (VMS) of the screws. Across all models, the proximal posterior screw exhibited the highest VMS values. Increasing model age was associated with higher mean stresses in the implants.\u003c/p\u003e","description":"","filename":"OnlineFig5.png","url":"https://assets-eu.researchsquare.com/files/rs-9411724/v1/55d61e95f100a2b3eb91f7dd.png"},{"id":107965817,"identity":"08ab0e95-146a-46c1-af97-e7050a2cf471","added_by":"auto","created_at":"2026-04-28 05:41:32","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":19633,"visible":true,"origin":"","legend":"\u003cp\u003eFracture risk index (FRI) in cancellous bone surrounding the screws versus model age. FRI in the cancellous bone surrounding the screws increased with model age.\u003c/p\u003e","description":"","filename":"OnlineFig6.png","url":"https://assets-eu.researchsquare.com/files/rs-9411724/v1/15984040ab8972617ee05546.png"},{"id":107965743,"identity":"19834382-9526-4f21-9582-a1347c7d051c","added_by":"auto","created_at":"2026-04-28 05:41:17","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":5713,"visible":true,"origin":"","legend":"\u003cp\u003eDistribution of fracture risk index (FRI) versus model age. Contour plots across different model ages (30–100 years, corresponding to A–H) show increased FRI with advancing model age, particularly in load-bearing regions, fracture sites, and around the screw threads. Warmer colors (red) indicate higher FRI values, while cooler colors (blue) indicate lower values (0–100).\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-9411724/v1/795cfe65360e25572a1e2b49.png"},{"id":107965746,"identity":"836ab016-0cb8-4e6d-b247-0f346d0ccff3","added_by":"auto","created_at":"2026-04-28 05:41:17","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":26142,"visible":true,"origin":"","legend":"\u003cp\u003eRelative displacement and fracture risk index (FRI) versus model age. Combined bar–line graph shows increased relative displacement and FRI of the cancellous bone surrounding the three screws with advancing model age.\u003c/p\u003e","description":"","filename":"OnlineFig8.png","url":"https://assets-eu.researchsquare.com/files/rs-9411724/v1/b113475461089554dcf05e56.png"},{"id":107965956,"identity":"03a90817-1a8f-4a8e-905a-a691a5086c41","added_by":"auto","created_at":"2026-04-28 05:42:03","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":600462,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9411724/v1/25ede61f-780a-4a8c-8fe6-697b5f947772.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Impact of Age-Related Decline in Bone Mineral Density on Internal Fixation for Nondisplaced Femoral Neck Fractures: A Finite Element Analysis Using Virtual Simulation Models","fulltext":[{"header":"Background","content":"\u003cp\u003eAs the global population ages, the prevalence of osteoporosis increases, resulting in a growing incidence of hip fractures, including femoral neck fractures (FNFs), with the total number of cases projected to reach approximately 6\u0026nbsp;million worldwide by 2050 [1, 2]. The conventional treatment strategies for FNFs are generally determined according to the Garden classification [3], which divides FNFs into four types based on displacement and fracture completeness and guides treatment decisions. Preservation of the femoral head is generally favored for Garden stages 1 and 2 (incomplete or complete nondisplaced fractures), whereas arthroplasty is indicated for Garden stages 3 and 4 (displaced fractures) [4]. However, in elderly patients, the optimal treatment strategy for nondisplaced FNFs remains controversial, as outcomes following osteosynthesis have been reported to be unsatisfactory in this population [5\u0026ndash;7].\u003c/p\u003e \u003cp\u003eOsteoporosis associated with aging disrupts the balance of bone resorption and formation, resulting in decreased bone mineral density (BMD), and impaired bone quality and microarchitecture [8]. Previous clinical studies have reported high rates of internal-fixation-related complications in elderly patients with nondisplaced hip fractures due to osteoporosis, including osteonecrosis, nonunion, implant-related complications, and persistent pain [6, 9, 10]. This is partly because traditional fixation methods, originally designed for healthy bone, may fail to provide sufficient stability in osteoporotic bone [8].\u003c/p\u003e \u003cp\u003eHowever, clinical studies evaluating internal fixation in osteoporotic femoral neck fractures are often affected by heterogeneity in femoral morphology, fracture patterns, and patient characteristics, making it difficult to isolate the specific biomechanical contribution of osteoporosis. Meanwhile, finite element analysis (FEA) has been introduced into the field of orthopedic surgery, enabling detailed biomechanical analysis of bone-implant constructs [11]. Using FEA, previous studies have investigated optimal internal fixation strategies for nondisplaced FNFs from perspectives such as implant type [12\u0026ndash;14], screw insertion angle [15, 16], and Pauwels angle [17\u0026ndash;21]. However, to the best of our knowledge, no previous study has specifically isolated the independent biomechanical effect of osteoporotic bone changes on fixation stability in nondisplaced FNFs.\u003c/p\u003e \u003cp\u003eThis study focused specifically on age-related, region-specific decline in BMD. The objectives were: (1) to establish a novel FEA-based evaluation method using virtual models that incorporate age-related BMD reduction; and (2) to elucidate the relationship between BMD and the mechanical stability of internal fixation for nondisplaced FNFs.\u003c/p\u003e"},{"header":"Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy design and setting\u003c/h2\u003e \u003cp\u003e This retrospective study was approved by the International Review Board of Graduate School of Medicine, University of the Ryukyus (#23-2188, Oct. 18th 2023). All procedures were performed in accordance with the principles of the Declaration of Helsinki. Informed consent was obtained by optout process. A healthy 30-year-old woman without a history of osteoporosis or fragility fracture with available pelvic computed tomography (CT) scan data was used for analysis. Preoperative data were obtained using 160-row spiral CT (Aquilion Precision, Canon Medical Systems Inc., Tochigi, Japan). Data with a 0.5-mm thickness were saved in Digital Imaging and Communications in Medicine format and were imported into quantitative CT/FEA software (MECHANICAL FINDER ver. 13, Research Center of Computational Mechanics, Inc., Tokyo, Japan).\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eModeling\u003c/h3\u003e\n\u003cp\u003eFirst, a horizontal line was created perpendicular to the proximal shaft axis of the femur. The fracture plane was then created and set at an angle of 70\u0026deg; to the horizontal line, creating a nondisplaced FNF model with a Pauwels angle of 70\u0026deg; (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). In our previous study, we demonstrated that the angular stability provided by a fixed angle device (FAD) is essential for resisting shear forces in Pauwels 70\u0026deg; FNFs [17]; therefore, the Prima Hip Screw Side Plate System (PHS\u0026thinsp;+\u0026thinsp;SP, Ortho Development Corporation, UT, USA) was selected as the internal fixation device in the present study. To create an ideal model of FAD fixation, all screw lengths were sufficient such that the screw tips were located within 3 mm of subchondral bone [22], the distal screw was positioned adjacent to the inner inferior cortex of the femoral neck, and the femoral plate was set parallel to the femoral shaft (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eMeshing\u003c/h3\u003e\n\u003cp\u003eMesh generation was performed using the extracted CT images of the femur and the stereolithographic data of the PHS\u0026thinsp;+\u0026thinsp;SP. The general element size was set to 2 mm. To allow region-specific adjustments of BMD, the femur was subdivided into five anatomical regions, including the femoral head, femoral neck, greater trochanter, intertrochanteric region, and femoral shaft (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e). The model consisted of 202,859 nodes and 893,379 elements. The mesh convergence test was conducted to validate this mesh size setting.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e\n\u003ch3\u003eMaterial properties and creating virtual models\u003c/h3\u003e\n\u003cp\u003eIn the quantitative CT/FEA software used in this study, volume-BMD (vBMD) is calculated from the Hounsfield unit (HU) of the imported CT images using a proprietary calibration curve and the conversion formula described below:\u003cdiv id=\"Equa\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equa\" name=\"EquationSource\"\u003e\n$$\\:vBMD\\:\\left(\\frac{g}{c{m}^{3}}\\right)=\\:\\frac{\\left\\{\\left(HU\\:+\\:1.42\\right)0.001\\right\\}}{1.058}$$\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eThe obtained BMD is then substituted into Keyak\u0026rsquo;s conversion equation to calculate the Young\u0026rsquo;s modulus [23]. Using the quantitative annual evolution of regional femoral BMD reported by Dudle et al. [24] (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), together with the aforementioned conversion formula, the integrated vBMD values were estimated at 10, 20, 30, 40, 50, 60, and 70 years in the future for each of the five regions. These values were then assigned to the corresponding regions as material properties to modify the original femur model, thereby generating eight virtual femur models simulating progressive aging. A Poisson\u0026rsquo;s ratio of 0.4 was set for the femur. For the titanium alloy, a Young\u0026rsquo;s modulus of 108,000 MPa and a Poisson\u0026rsquo;s ratio of 0.28 were assigned to PHS\u0026thinsp;+\u0026thinsp;SP [25].\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eQuantitative annual change in regional femoral BMD reported by Dudle et al. [24]\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFemoral head\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFemoral neck\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eGreater trochanter\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eIntertrochanteric region\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eFemoral shaft\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAnnual change in BMD (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026ndash;0.54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026ndash;0.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026ndash;0.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026ndash;0.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026ndash;0.44\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eBMD, bone mineral density.\u003c/p\u003e\n\u003ch3\u003eContact conditions\u003c/h3\u003e\n\u003cp\u003eBased on previous studies, the friction coefficients for the bone\u0026ndash;bone and bone\u0026ndash;screw interfaces were 0.46 and 0.42, respectively. To recreate the barrel mechanism of the PHS\u0026thinsp;+\u0026thinsp;SP, the screws were divided into outer and inner parts and were assigned frictional contact, with a friction coefficient of 0.2 [26]. The femoral plate/outer part of the PHS and the femoral plate/bone interfaces were assumed to be fixed.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eBoundary conditions\u003c/h2\u003e \u003cp\u003eTo simulate the single-leg standing position, the model was abducted 10\u0026deg; and tilted backward by 9\u0026deg; [27]. A downward force of three times the body weight (1500 N) was applied to the surface of the femoral head [12] (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). The distal end of the femur was embedded in a soft material (Young\u0026rsquo;s modulus\u0026thinsp;=\u0026thinsp;0.2, Poisson\u0026rsquo;s ratio\u0026thinsp;=\u0026thinsp;0.3) to prevent excessive stress around the fixed area, and the material was fixed in all directions [28].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eEvaluation\u003c/h3\u003e\n\u003cp\u003eLinear analysis was conducted. The mean von Mises stress (VMS) of the three screws of the PHS\u0026thinsp;+\u0026thinsp;SP was evaluated individually. To evaluate the stability of the screws, a region of interest (ROI) was defined in the bone surrounding the screws, and mean fracture risk index (FRI) [29] of the ROI was compared between the two models. The FRI is defined as the ratio of the VMS to yield stress, averaged over the ROI, with a higher FRI indicating an increased likelihood of element failure and a greater risk of screw loosening. For fracture stability, the average relative displacement of the fracture surface was evaluated as the amount of fracture fragment displacement.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e summarizes the estimated integrated vBMD values for each femoral region in the original model and at simulated aging stages from 10 to 70 years. A gradual decrease in vBMD was observed across all femoral regions with increasing simulated age.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eEstimated integral volume bone mineral density for each femoral region in age-specific virtual models\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eFemoral region\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"8\" nameend=\"c9\" namest=\"c2\"\u003e \u003cp\u003eModel age (years)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e60\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e80\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003e100\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFemoral head\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e251\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e238\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e225\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e213\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e202\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e191\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e181\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e172\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFemoral neck\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e454\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e424\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e396\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e370\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e346\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e323\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e302\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e282\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGreater trochanter\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e378\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e360\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e343\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e327\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e312\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e297\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e283\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e270\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eIntertrochanteric region\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e309\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e287\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e266\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e247\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e229\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e212\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e197\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e183\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eFemoral shaft\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e600\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e574\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e549\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e526\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e503\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e481\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e461\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c9\"\u003e \u003cp\u003e441\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAll values of bone mineral density are provided in mg/cm\u003csup\u003e3\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIncreasing model age was associated with higher mean implant VMS values (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e). Consistently, the mean FRI values of the cancellous bone surrounding the screws also increased with age (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). Contour plots demonstrated a marked increase in FRI, particularly in load-bearing regions, fracture sites, and around the screw threads (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). In addition, the relative displacement of fracture fragment increased with advancing model age, accompanied by a concomitant increase in the mean FRI of cancellous bone surrounding the three screws (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eTo our knowledge, no previous studies have visualized biomechanical changes associated with age-related declines in vBMD during internal fixation for nondisplaced FNF using FEA. The most important finding of the present study is that age-related, region-specific reductions in vBMD alone significantly affect the mechanical stability of internal fixation for nondisplaced FNFs. As model age increased, the VMS of the implant as well as the FRI of the cancellous bone around the screws progressively increased, and fracture fragment displacement became greater. These findings suggest that a decrease in vBMD itself plays a substantial role in fixation instability, even when fracture morphology and implant configuration are identical.\u003c/p\u003e \u003cp\u003eClinical studies have reported unsatisfactory outcomes after internal fixation in elderly patients with nondisplaced FNFs [30]. However, interpretation of these findings is difficult because of confounding factors such as variability in femoral morphology, fracture configuration, implant positioning, and patient-related characteristics. By constructing virtual models in which only vBMD was modified according to age-related regional decline while maintaining other factors constant, the present study isolated the independent biomechanical effect of vBMD reduction. This approach enables a direct mechanical explanation for the higher complication rates observed in elderly patients.\u003c/p\u003e \u003cp\u003eThe magnitude of vBMD reduction implemented in the present virtual models appears reasonable. A previous study by Gamio et al. reported femoral neck integral vBMD values of 404 mg/cm\u003csup\u003e3\u003c/sup\u003e in 94 young women (mean age, 34 years) and 294 mg/cm\u003csup\u003e3\u003c/sup\u003e in 157 elderly women (mean age, 79 years), all without a history of fragility fractures [31]. Wu et al. assessed femoral neck vBMD in postmenopausal women using quantitative multi-slice CT and reported that the value of integrated femoral neck vBMD was 347.1 mg/cm\u003csup\u003e3\u003c/sup\u003e in the group without osteoporosis or a history of vertebral fracture (mean age, 56.8 years) [32]. The vBMD values of the original model and the virtual models generated in this study were comparable to these reported values, supporting the validity of the present models.\u003c/p\u003e \u003cp\u003eFor uneventful fracture healing, certain conditions are required of the bone/implant construct, including mechanically sound fixation. Implant fatigue and screw loosening may jeopardize maintenance of fracture healing [33]. Previous studies have demonstrated a strong positive correlation between BMD and elastic modulus at the bulk scale, indicating that reductions in BMD are associated with decreased bone stiffness and yield strength [34, 35]. As the mechanical competence of cancellous bone depends largely on BMD, a reduction in BMD diminishes the bone\u0026rsquo;s capacity to withstand mechanical loading [4]. As a consequence, stress concentrations increase at the screw-bone interface, particularly in load-bearing regions and screw threads, as reflected by the elevated FRI observed in the present study. Between ages 30 and 80, FRI increased by approximately 31 (125%) in the distal screw, 26 (103%) in the proximal posterior screw, and 23 (101%) in the proximal anterior screw, with the greatest increase observed in the distal screw. Such stress concentrations may promote microdamage accumulation and contribute to progressive screw loosening over time [36]. Furthermore, the increased displacement of the fracture fragments with advancing model age suggests reduced construct stiffness, a condition that is particularly critical in Pauwels 70\u0026deg; fractures where shear forces predominate.\u003c/p\u003e \u003cp\u003eA previous investigation has shown that local mechanical quality of the bone, as well as the predicted magnitude of its loading, are important parameters for assessing the loosening risk of the screws [36]. The study mainly focused on pull-out behavior of the screws, in which tensile failure represents the primary failure mode, and therefore used failure strength as the reference parameter. In contrast, in the present study, compressive deformation was considered the dominant mechanical response. Thus, we adopted FRI as a parameter to assess the risk of screw loosening, defined as the ratio of VMS to yield stress of the bone. The yield stress represents the threshold at which bone begins to undergo plastic deformation under compression [23].\u003c/p\u003e \u003cp\u003eFrom a clinical perspective, surgeons should bear in mind that even in cases with identical fracture displacement or Pauwels angle, differences in bone mineral density may require different treatment strategies. The present study demonstrated that poor bone quality may compromise fixation stability. Therefore, assessment of BMD is essential when selecting the most appropriate patient-specific treatment strategy. In patients with severe osteoporosis, particularly those with steep Pauwels angles, surgeons should not base the decision for internal fixation solely on the absence of fracture displacement. Instead, careful consideration should be given to implant selection and surgical strategy, and alternative approaches such as arthroplasty may be considered [7, 37\u0026ndash;40].\u003c/p\u003e \u003cp\u003eThe present study had several limitations. It did not incorporate impaired bone quality and microarchitecture, which are also important changes associated with aging. Future models including bone quality deterioration may provide a more comprehensive understanding; nevertheless, isolating the effect of vBMD reduction allowed us to clarify its independent biomechanical contribution to fixation stability. Moreover, the effects of soft tissues, such as muscles and ligaments, were not simulated in our study. Despite these limitations, this study had several strengths. The analysis was based on CT data from an existing case, incorporating the nonlinear material properties of the bone. In addition, region-specific age-related reductions in vBMD were subdivided into five anatomical regions, and a total of eight well-established FEA models were generated to reflect these regional differences. This modeling strategy enabled a more realistic representation of age-related femoral changes. By integrating longitudinal vBMD evolution data into patient-specific FEA models, the present study provides a novel methodological framework that may be applied to other osteoporotic fracture analyses.\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eBy applying FEA, we successfully developed models that represent region-specific changes in femoral vBMD associated with aging. Using these models, we demonstrated that reductions in vBMD increased the risk of screw loosening and resulted in greater fracture displacement. These findings provide biomechanical evidence supporting the importance of bone quality assessment when selecting surgical strategies for FNFs, especially in elderly patients.\u003c/p\u003e"},{"header":"Abbreviations","content":" \u003cp\u003eFNF Femoral neck fracture\u003c/p\u003e \u003cp\u003eBMD Bone mineral density\u003c/p\u003e \u003cp\u003eFEA Finite element analysis\u003c/p\u003e \u003cp\u003eCT Computed tomography\u003c/p\u003e \u003cp\u003eFAD Fixed angle device\u003c/p\u003e \u003cp\u003ePHS\u0026thinsp;+\u0026thinsp;SP Prima Hip Screw Side Plate System\u003c/p\u003e \u003cp\u003ev-BMD Volume bone mineral density\u003c/p\u003e \u003cp\u003eHU Hounsfield unit\u003c/p\u003e \u003cp\u003eVMD Von Mises stress\u003c/p\u003e \u003cp\u003eROI Region of interest\u003c/p\u003e \u003cp\u003eFRI Fracture risk index\u003c/p\u003e "},{"header":"Declarations","content":"\u003cp\u003e \u003cstrong\u003eEthics approval and consent to participate\u003c/strong\u003e \u003cp\u003eThis retrospective study was approved by the International Review Board of Graduate School of Medicine, University of the Ryukyus (#23-2188, Oct. 18th 2023). All procedures were performed in accordance with the principles of the Declaration of Helsinki. Informed consent was obtained by optout process.\u003c/p\u003e \u003ch2\u003eConsent for publication\u003c/h2\u003e \u003cp\u003eNot applicable.\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eCompeting interests:\u003c/strong\u003e \u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e \u003ch2\u003eFunding:\u003c/h2\u003e \u003cp\u003eThis study was supported by a Grant in Aid for Scientific Research (C) (General) 2027\u0026ndash;2029.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eSK: Design of this study, Finite element analysis, Drafting. SN: Revising the article for important intellectual content. KO: Advice on model development. MT, FW: Interpretation of the results. KN: Final approval of the version to be submitted.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors are grateful to Research Center of Computational Mechanics for their technical advises in using MECHANICAL FINDER ver.13.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003e Data is provided within the manuscript. And all data used and analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eCauley JA. Public health impact of osteoporosis. \u003cem\u003eJournal of Gerontology Series A: Biological Sciences and Medical Sciences\u003c/em\u003e. 2013; 68:1243\u0026ndash;1251.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKaragas MR, et al. Heterogeneity of hip fracture: age, race, sex, and geographic patterns of femoral neck and trochanteric fractures among the US elderly. \u003cem\u003eAmerican Journal of Epidemiology\u003c/em\u003e. 1996; 143:677\u0026ndash;682.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGarden RS. Low-angle fixation in fractures of the femoral neck. \u003cem\u003eJournal of Bone and Joint Surgery British Volume\u003c/em\u003e. 1961; 43:647\u0026ndash;663.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKazley JM, et al. Classifications in brief: Garden classification of femoral neck fractures. \u003cem\u003eClinical Orthopaedics and Related Research\u003c/em\u003e. 2018; 476:441\u0026ndash;445.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGoh JC, Shah KM, Bose K. Biomechanical study on femoral neck fracture fixation in relation to bone mineral density. \u003cem\u003eClinical Biomechanics\u003c/em\u003e. 1995; 10:304\u0026ndash;308.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKim SJ, Park HS, Lee DW. Complications after internal screw fixation of nondisplaced femoral neck fractures in elderly patients: a systematic review. \u003cem\u003eActa Orthopaedica et Traumatologica Turcica\u003c/em\u003e. 2020; 54:337\u0026ndash;343.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHan SK, et al. Clinical results of treatment of Garden type 1 and 2 femoral neck fractures in patients over 70-year-old. \u003cem\u003eEuropean Journal of Trauma and Emergency Surgery\u003c/em\u003e. 2016; 42:191\u0026ndash;196.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMukhopadhaya J, Bhadani JS. 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Outcomes of elderly patients with nondisplaced or minimally displaced femoral neck fractures treated with internal fixation: a systematic review and meta-analysis. \u003cem\u003eInjury\u003c/em\u003e. 2019; 50:2158\u0026ndash;2166.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"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":"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":"Bone mineral density, Finite element analysis, Nondisplaced femoral neck fracture, Osteoporosis, Virtual model, Pauwels Type III","lastPublishedDoi":"10.21203/rs.3.rs-9411724/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9411724/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eAs the global population ages, the incidence of femoral neck fractures (FNFs) is rising. While internal fixation is generally preferred for nondisplaced FNFs, clinical outcomes in elderly patients remain controversial due to high complication rates associated with osteoporosis. This study aimed to establish a novel finite element analysis (FEA)-based evaluation method using virtual models to isolate the independent biomechanical effect of age-related, region-specific decline in bone mineral density (BMD) on the stability of internal fixation for nondisplaced FNFs.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eA 70\u0026deg; Pauwels angle nondisplaced FNF model was created using CT data from a 30-year-old woman and was fixed with a fixed angle device. Eight virtual femur models, simulating ages 30 to 100, were generated by adjusting regional volume-BMD (vBMD) based on established longitudinal aging data. Linear FEA was performed to simulate single-leg standing. Evaluation parameters included mean von Mises stress (VMS) on screws, the fracture risk index (FRI) of the surrounding cancellous bone, and the relative displacement of the fracture fragments.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003e Increasing simulated model age was associated with progressive decrease in regional vBMD across all areas. This decline led to a concomitant increase in mean implant VMS and the FRI of the bone surrounding the screws, particularly in load-bearing regions and around screw threads. Between simulated ages 30 and 80, the FRI increased by 101% to 125% across the three screws, with the distal screw showing the greatest increase. Furthermore, fracture fragment displacement increased with advancing model age, indicating reduced construct stiffness.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eAge-related reduction in vBMD alone significantly compromises the biomechanical stability of internal fixation in nondisplaced FNFs, even when fracture morphology and implant configuration are identical. These findings suggest that BMD assessment is essential for surgical planning; in cases of severe osteoporosis, surgeons may need to consider alternative strategies, such as arthroplasty, despite the absence of fracture displacement.\u003c/p\u003e","manuscriptTitle":"Impact of Age-Related Decline in Bone Mineral Density on Internal Fixation for Nondisplaced Femoral Neck Fractures: A Finite Element Analysis Using Virtual Simulation Models","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-28 05:39:46","doi":"10.21203/rs.3.rs-9411724/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-05-10T09:14:57+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"23592253330549940054520301452228514243","date":"2026-04-19T13:44:32+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-19T13:36:24+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-04-17T14:22:59+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-04-16T11:31:58+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-04-16T11:31:56+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Musculoskeletal Disorders","date":"2026-04-14T06:57:44+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":"91d93ba8-0fb9-4169-9c33-1c186ddc456e","owner":[],"postedDate":"April 28th, 2026","published":true,"recentEditorialEvents":[{"type":"editorInvitedReview","content":"","date":"2026-05-10T09:14:57+00:00","index":36,"fulltext":""}],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-28T05:39:46+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-28 05:39:46","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9411724","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9411724","identity":"rs-9411724","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}