Cement augmentation of calcar screws may provide the greatest reduction in predicted screw cut-out risk for proximal humerus plating based on validated parametric computational modelling: Augmenting proximal humerus fracture plating

Biomechanical study of two different fixation methods for the treatment of Neer III proximal humerus fractures

BACKGROUND

The lateral locking plate for the proximal humerus is currently the most commonly used surgical procedure for the treatment of elderly proximal humeral comminuted fractures. Previous studies have found that the rate of postoperative complications in patients of proximal humerus fractures with medial column involvement is relatively high. Through biomechanical methods, this study aims to investigate the effectiveness of the conventional lateral locking plate fixation along with the addition of the metacarpal supporting plate on the medial column in the treatment for proximal humeral fractures involving the medial column. The goal is to reduce the rate of postoperative internal fixation failure in patients with medial column injury.

METHODS

Thirty artificial synthetic humerus models are used as experimental samples. A proximal humerus fracture model with medial column injury was created, and then divided into two groups. Group A was fixed with a proximal humerus lateral locking plate (single-plate group). Group B was fixed with a proximal humerus lateral locking plate and a metacarpal supporting plate on the medial column (double-plate group). The failure displacement, stiffness, and strength of the repaired proximal humerus fractures with two different methods were tested under compression at posterior extension of 15°, forward flexion of 15°, and vertical direction.

RESULTS

There was no statistical significance in the comparison of the failure displacement of repaired proximal humeral fractures between the two groups under compression at posterior extension of 15° and forward flexion of 15° (P > 0.05). However, the failure displacement of the fracture was longer in single-plate group than in double-plate group under compression at vertical direction (P < 0.05). The double-plate group was better in terms of biomechanical stiffness and strength compared to the single-plate group at all three testing angles (P < 0.05).

CONCLUSIONS

For patients whose proximal humeral fractures involve the medial column, the addition of a support plate on the medial side of the humerus is recommended along with the lateral locking plate. The double-plate strategy can increase the stability of the medial column of the proximal humerus, and enhance the overall biomechanical property of the repaired proximal humerus.

Hip joint center lateralization minimally affects the biomechanics of patient-specific flanged acetabular components: A computational model

Patient-specific flanged acetabular components are utilized to treat failed total hip arthroplasties with large acetabular defects. Previous clinical studies from our institution showed that these implants tend to lateralize the acetabular center of rotation. However, the clinical impact of lateralization on implant survivorship is debated. Our goal was to develop a finite element model to quantify how lateralization of the native hip center affects periprosthetic strain and implant-bone micromotion distributions in a static level gait loading condition. To build the model, we computationally created a superomedial acetabular defect in a computed tomography 3D reconstruction of a native pelvis and designed a flanged acetabular implant to address this simulated bone defect. We modeled two implants, one with ~1 cm and a second with ~2 cm of hip center lateralization. We applied the maximum hip contact force and corresponding abductor force observed during level gait. The resulting strains were compared to bone fatigue strength (0.3% strain) and the micromotions were compared to the threshold for bone ingrowth (20 µm). Overall, the model demonstrated that the additional lateralization only slightly increased the area of bone at risk of failure and decreased the areas compatible with bone ingrowth. This computational study of patient-specific acetabular implants establishes the utility of our modeling approach. Further refinement will yield a model that can explore a multitude of variables and could be used to develop a biomechanically-based acetabular bone loss classification system to guide the development of patient-specific implants in the treatment of large acetabular bone defects.

Cyclic Stability of Locking Plate Augmented with Intramedullary Polymethyl Methacrylate (PMMA) Strut Fixation for Osteoporotic Humeral Fractures: A Biomechanical Study

The locking plate may provide improved fixation in osteoporotic bone; however, it has been reported to fail due to varus collapse or screw perforation of the articular surface, especially in osteoporotic bone with medial cortex comminution. Using bone graft as an intramedullary strut together with plate fixation may result in a stronger construct. However, the drawbacks of bone grafts include limited supply, high cost, and infection risk. PMMA (so-called bone cement) has been widely used for implant fixation due to its good mechanical properties, fabricability, and biocompatibility. The risk of donor-site infection and the drawbacks of allografting may be overcome by considering PMMA struts as alternatives to fibular grafts for humeral intramedullary grafting surgeries. However, the potential effects of intramedullary PMMA strut on the dynamic behaviour of osteoporotic humerus fractures remain unclear. This study aimed to investigate the influence of an intramedullary PMMA strut on the stability of unstable proximal humeral fractures in an osteoporotic synthetic model. Two fixation techniques, a locking plate alone (non-strut group) and the same fixation augmented with an intramedullary PMMA strut (with-strut group), were cyclically tested in 20 artificial humeral models. Axially cyclic testing was performed to 450 N for 10,000 cycles, intercyclic motion, cumulated fragment migration, and residual deformation of the constructs were determined at periodic cyclic intervals, and the groups were compared. Results showed that adding an intramedullary PMMA strut could decrease 1.6 times intercyclic motion, 2 times cumulated fracture gap migration, and 1.8 times residual deformation from non-strut fixation. During cycling, neither screw pull-out, cut-through, nor implant failure was observed in the strut-augmented group. We concluded that the plate-strut mechanism could enhance the cyclic stability of the fixation and minimize the residual displacement of the fragment in treating osteoporotic proximal humeral unstable fractures. The PMMA strut has the potential to substitute donor bone and serve as an intramedullary support when used in combination with locking plate fixation. The intramedullary support with bone cement can be considered a solution in the treatment of osteoporotic proximal humeral fractures, especially when there is medial comminution.

Plate Fixation of Proximal Humerus Fractures: How to Get It Right and Future Directions for Improvement

PURPOSE OF REVIEW

Open reduction and internal fixation with locking plates (ORIF-LP) has been used for decades for the surgical management of proximal humerus fractures. Despite good outcomes have been widely published in the literature, unacceptably high rates of complications (up to 40%), many of them yielding poor outcomes and requiring reoperation (up to 25%), have also been reported, especially in elderly patients. Most common complications are related to implant failure, with intra-articular screw penetration as the most frequent and devastating.

RECENT FINDINGS

Advances in patient selection and surgical technique, and implementation of bone or cement augmentation, have been developed to hopefully decrease complication rates. Mayo-FJD Classification offers prognostic information that can aid in the decision-making process for proximal humeral fractures. Displaced valgus impacted fractures seem to be associated with well over a 10% rate of avascular necrosis after ORIF-LP. A principle-based and stepwise surgical technique combining anatomic reduction and a short screw configuration can provide good outcome in most patients, even the elderly, decreasing implant failures to less than 10%. Acrylic cement augmentation has the potential to further decrease implant failure rate to 1%. Reoperation rates are higher partly due to the need to remove hardware for painful subacromial conflict. However, no studies to date definitively demonstrated the superiority of ORIF-LP compared to non-operative treatment, intramedullary nailing, or reverse shoulder arthroplasty. ORIF-LP can provide good results for the surgical management of displaced proximal humerus fractures even in elderly patients provided adequate patient selection and a principle based and stepwise surgical technique, supplemented with bone graft or acrylic cement when needed. Poor outcomes and high complication and reoperation rates should be expected when these recommendations are not followed.

[Translated article] Comparative biomechanical study of two configurations of cemented screws in a simulated proximal humerus fracture fixed with locking plate

INTRODUCTION

Screw tip augmentation with bone cement for fixation of osteoporotic proximal humerus fractures seems to improve stability and to decrease the rate of complications related to implant failure. However, the optimal augmentation combinations are unknown. The aim of this study was to assess the relative stability of two augmentations combinations under axial compression load in a simulated proximal humerus fractures fixed with locking plate.

MATERIAL AND METHODS

A surgical neck osteotomy was created in five pairs of embalmed humeri with a mean age of 74 years (range 46-93 years), secured with a stainless-steel locking-compression plate. In each pair of humeri, on the right humerus were cemented the screws A and E, and in the contralateral side were cemented screws B and D of the locking plate. The specimens were first tested cyclically in axial compression for 6000 cycles to evaluate interfragmentary motion (dynamic study). At the end of the cycling test, the specimens were loaded in compression force simulating varus bending with increasing load magnitude until failure of the construct (static study).

RESULTS

There were no significant differences in interfragmentary motion between the two configurations of cemented screws in the dynamic study (p=0.463). When tested to failure, the configuration of cemented screws in lines B and D demonstrated higher compression load to failure (2218N vs. 2105, p=0.901) and higher stiffness (125N/mm vs. 106N/mm, p=0.672). However, no statistically significant differences were reported in any of these variables.

CONCLUSIONS

In simulated proximal humerus fractures, the configuration of the cemented screws does not influence the implant stability when a low-energy cyclical load is applied. Cementing the screws in rows B and D provides similar strength to the previously proposed cemented screws configuration and could avoid complications observed in clinical studies.

Double Plating for Complex Proximal Humeral Fractures: Clinical and Radiological Outcomes

Double plating for proximal humeral fractures (PHF) is an option to increase the primary fixation stability. Clinical data is missing for assessment of clinical and radiological outcome, as well as complications. We retrospectively examined 35 patients with unilateral PHF, who were treated with double plating for PHF between 2013 and 2019. The mean age was 59.5 ± 12 years and the leading fracture type was a varus dislocation (Resch type IV in 55.3%). A head-split was present in 22.9% of the cases. The primary outcome measurement was the radiological neck shaft angle (NSA). The radiological follow-up was 21 ± 16.6 months and the NSA did not differ between the intraoperative and follow-up time point (131.5 ± 6.9° vs. 136.6 ± 13.7°; p = 0.267). The clinical follow-up was 29.5 ± 15.3 months. The Constant-score was 78.5 ± 17 points, the simple-shoulder-test (SST) was 9.3 ± 3.2 points and the subjective shoulder value (SSV) was 78.8 ± 19.5%. The over-all complication rate was 31.4%, and without stiffness 14.3%. An avascular necrosis occurred in two patients (5.7%). In conclusion, this study shows good radiological and functional outcomes after double plating of highly complex proximal humeral fractures, while the complication rate is comparable to the literature. Double plating is a viable option especially for younger patients with complex fractures as a potential alternative to fracture arthroplasty.

Comparative biomechanical study of two configurations of cemented screws in a simulated proximal humerus fracture fixed with locking plate

INTRODUCTION

Screw tip augmentation with bone cement for fixation of osteoporotic proximal humerus fractures seems to improve stability and to decrease the rate of complications related to implant failure. However, the optimal augmentation combinations are unknown. The aim of this study was to assess the relative stability of two augmentations combinations under axial compression load in a simulated proximal humerus fractures fixed with locking plate.

MATERIAL AND METHODS

A surgical neck osteotomy was created in five pairs of embalmed humeri with a mean age of 74 years (range 46-93 years), secured with a stainless-steel locking-compression plate. In each pair of humeri, on the right humerus were cemented the screws A and E, and in the contralateral side were cemented screws B and D of the locking plate. The specimens were first tested cyclically in axial compression for 6,000 cycles to evaluate interfragmentary motion (dynamic study). At the end of the cycling test, the specimens were loaded in compression force simulating varus bending with increasing load magnitude until failure of the construct (static study).

RESULTS

There were no significant differences in interfragmentary motion between the two configurations of cemented screws in the dynamic study (p=0.463). When tested to failure, the configuration of cemented screws in lines B and D demonstrated higher compression load to failure (2218N vs. 2105, p=0.901) and higher stiffness (125N/mm vs. 106N/mm, p=0.672). However, no statistically significant differences were reported in any of these variables.

CONCLUSIONS

In simulated proximal humerus fractures, the configuration of the cemented screws does not influence the implant stability when a low-energy cyclical load is applied. Cementing the screws in rows B and D provides similar strength to the previously proposed cemented screws configuration and could avoid complications observed in clinical studies.

Locking Plates With Computationally Enhanced Screw Trajectories Provide Superior Biomechanical Fixation Stability of Complex Proximal Humerus Fractures

Joint-preserving surgical treatment of complex unstable proximal humerus fractures remains challenging, with high failure rates even following state-of-the-art locked plating. Enhancement of implants could help improve outcomes. By overcoming limitations of conventional biomechanical testing, finite element (FE) analysis enables design optimization but requires stringent validation. This study aimed to computationally enhance the design of an existing locking plate to provide superior fixation stability and evaluate the benefit experimentally in a matched-pair fashion. Further aims were the evaluation of instrumentation accuracy and its potential influence on the specimen-specific predictive ability of FE. Screw trajectories of an existing commercial plate were adjusted to reduce the predicted cyclic cut-out failure risk and define the enhanced (EH) implant design based on results of a previous parametric FE study using 19 left proximal humerus models (Set A). Superiority of EH versus the original (OG) design was tested using nine pairs of human proximal humeri (N = 18, Set B). Specimen-specific CT-based virtual preoperative planning defined osteotomies replicating a complex 3-part fracture and fixation with a locking plate using six screws. Bone specimens were prepared, osteotomized and instrumented according to the preoperative plan via a standardized procedure utilizing 3D-printed guides. Cut-out failure of OG and EH implant designs was compared in paired groups with both FE analysis and cyclic biomechanical testing. The computationally enhanced implant configuration achieved significantly more cycles to cut-out failure compared to the standard OG design (p &lt; 0.01), confirming the significantly lower peri-implant bone strain predicted by FE for the EH versus OG groups (p &lt; 0.001). The magnitude of instrumentation inaccuracies was small but had a significant effect on the predicted failure risk (p &lt; 0.01). The sample-specific FE predictions strongly correlated with the experimental results (R2 = 0.70) when incorporating instrumentation inaccuracies. These findings demonstrate the power and validity of FE simulations in improving implant designs towards superior fixation stability of proximal humerus fractures. Computational optimization could be performed involving further implant features and help decrease failure rates. The results underline the importance of accurate surgical execution of implant fixations and the need for high consistency in validation studies.

Factors influencing surgical management of proximal humerus fractures: do shoulder and trauma surgeons differ?

BACKGROUND

Proximal humerus fractures (PHFs) are managed with open reduction and internal fixation (ORIF), hemiarthroplasty (HA), reverse shoulder arthroplasty (RSA), or nonoperatively. Given the mixed results in the literature, the optimal treatment is unclear to surgeons. The purpose of this study was to survey orthopedic shoulder and trauma surgeons to identify the patient- and fracture-related characteristics that influence surgical decision-making.

METHODS

We distributed a 23-question closed-response email survey to members of the American Shoulder and Elbow Surgeons and Orthopaedic Trauma Association. Questions posed to respondents included demographics, surgical planning, indications for ORIF and arthroplasty, and the use of surgical augmentation with ORIF. Numerical and multiple-choice responses were compared between shoulder and trauma surgeons using unpaired t-tests and χ² tests, respectively.

RESULTS

Respondents included 172 shoulder and 78 trauma surgeons. When surgery is indicated, most shoulder and trauma surgeons treat 2-part (69%) and 3-part (53%) PHFs with ORIF. Indications for managing PHFs with arthroplasty instead of ORIF include an intra-articular fracture (82%), bone quality (76%), age (72%), and previous rotator cuff dysfunction (70%). In patients older than 50 years, 90% of respondents cited a head-split fracture as an indication for arthroplasty. Both shoulder and trauma surgeons preferred RSA for treating PHFs presenting with a head-split fracture in an elderly patient (94%), pre-existing rotator cuff tear (84%), and pre-existing glenohumeral arthritis with an intact cuff (75%). Similarly, both groups preferred ORIF for PHFs in young patients with a fracture dislocation (94%). In contrast, although most trauma surgeons preferred to manage PHFs in low functioning patients with a significantly displaced fracture or nonreconstructable injury nonoperatively (84% and 86%, respectively), shoulder surgeons preferred either RSA (44% and 46%, respectively) or nonoperative treatment (54% and 49%, respectively) (P < .001). Similarly, although trauma surgeons preferred to manage PHFs in young patients with a head-split fracture or limited humeral head subchondral bone with ORIF (98% and 87%, respectively), shoulder surgeons preferred either ORIF (54% and 62%, respectively) or HA (43% and 34%, respectively) (P < .001).

CONCLUSIONS

ORIF and HA are preferred for treating simple PHFs in young patients with good bone quality or fracture dislocations, whereas RSA and nonoperative management are preferred for complex fractures in elderly patients with poor bone quality, rotator cuff dysfunction, or osteoarthritis. The preferred management differed between shoulder and trauma surgeons for half of the common PHF presentations, highlighting the need for future research.

[Cement augmentation and bone graft substitutes-Materials and biomechanics]

BACKGROUND

Materials with different characteristics are used for cement augmentation and as bone graft substitutes.

OBJECTIVE

Cement augmentation and bone graft substitutes are the subject of current research. The evaluation of new knowledge allows its specific application.

MATERIAL AND METHODS

Selective literature search and outline of experimental research results on cement augmentation and bone graft substitutes.

RESULTS

Augmentation and bone graft substitutes are essential components of current trauma surgical procedures. Despite intensive research all materials have specific disadvantages. Cement augmentation of implants enhances not only the anchorage but also influences the failure mode.

CONCLUSION

Cement augmentation has large potential especially in osteoporotic bone. In load-bearing regions acrylic-based cements remain the standard of choice. Ceramic cements are preferred in non-load-bearing areas. Their combination with resorbable metals offers still largely unexplored potential. Virtual biomechanics can help improve the targeted application of cement augmentation.

[Augmentation in the treatment of proximal humeral and femoral fractures]

BACKGROUND

Proximal humeral and trochanteric femoral fractures in older patients are typically caused by low-energy trauma and are therefore often associated with osteoporosis. The treatment of such fragility fractures can be difficult as implant purchase is reduced in osteoporotic bone. By augmenting the fixation with cement the contact surface between implant and bone can be increased, which improves the stability of the osteosynthesis.

OBJECTIVE

This article describes the operative technique for the augmentation of trochanteric femoral fractures treated with the Trochanteric Fixation Nail-Advanced (TFNA, DePuy Synthes, Oberdorf BL, Switzerland) and proximal humeral fractures stabilized with a PHILOS plate (DePuy Synthes). Furthermore, the evidence for the augmentation of these two fracture types is elucidated.

RESULTS

Biomechanical studies could show an improved stability of the osteosynthesis after successful augmentation for both fracture types. The current evidence also indicates a clinical reduction of fixation failure. Whether the augmentation has an influence on the functional result could so far not yet clearly be proven.

CONCLUSION

Augmentation seems to be a safe and valuable addition to available treatment options especially for patients with fragility fractures.

Primary stability of cement augmentation in locking plate fixation for proximal humeral fractures: A comparison of absorbable versus non-absorbable cement

BACKGROUND

Cement augmentation has been suggested to increase the stability of screw anchoring in osteoporotic humeral fractures. Initial results are promising but may be jeopardized by cement leakage into the joint and difficult implant removal. Absorbable cement might have advantages in this regard, but it is unclear if the primary stability of both techniques is equivalent to each other. Therefore, this study aimed to compare its primary stability with that of non-absorbable cement augmentation.

METHODS

Nineteen cadaveric humeri with two-part fracture models were treated with locking plate osteosynthesis and cement augmentation using either absorbable calcium phosphate cement (group 1) or polymethylmethacrylate (group 2). Fracture movement, stiffness, failure mode, and ultimate load under cyclic compressive loading were examined and compared between the groups.

FINDINGS

The absolute and relative stiffness values in group 1 were significantly smaller than those in group 2 after 50 cycles (group 1: 114 ± 38 N/mm and 94 ± 8% vs. group 2: 188 ± 71 N/mm and 106 ± 9%; p₅₀ = 0.022), 2000 cycles (group 1: 97 ± 34 N/mm and 81 ± 15% vs. group 2: 153 ± 47 N/mm and 88 ± 15%; p₂₀₀₀ = 0.028), and 5000 cycles (group 1: 98 ± 40 N/mm and 81 ± 22% vs. group 2: 158 ± 40 N/mm and 92 ± 16%; p₅₀₀₀ = 0.028). The failure load was not statistically significantly different between the groups.

INTERPRETATION

Although the PMAA group showed higher values for absolute and relative stiffness, no statistically significant difference was found in the primary stability between absorbable and non-absorbable cement augmentation supporting plate osteosynthesis in proximal humeral fractures. In view of the potential advantages of bio-absorbable cement during the healing process, its use should be considered for the augmentation and stabilization of osteoporotic fractures.

The effect of cement augmentation on pedicle screw fixation under various load cases : results from a combined experimental, micro-CT, and micro-finite element analysis

Aims

Anchorage of pedicle screw rod instrumentation in the elderly spine with poor bone quality remains challenging. Our study aims to evaluate how the screw bone anchorage is affected by screw design, bone quality, loading conditions, and cementing techniques.

Methods

Micro-finite element (µFE) models were created from micro-CT (μCT) scans of vertebrae implanted with two types of pedicle screws (L: Ennovate and R: S⁴). Simulations were conducted for a 10 mm radius region of interest (ROI) around each screw and for a full vertebra (FV) where different cementing scenarios were simulated around the screw tips. Stiffness was calculated in pull-out and anterior bending loads.

Results

Experimental pull-out strengths were excellently correlated to the µFE pull-out stiffness of the ROI (R² > 0.87) and FV (R² > 0.84) models. No significant difference due to screw design was observed. Cement augmentation increased pull-out stiffness by up to 94% and 48% for L and R screws, respectively, but only increased bending stiffness by up to 6.9% and 1.5%, respectively. Cementing involving only one screw tip resulted in lower stiffness increases in all tested screw designs and loading cases. The stiffening effect of cement augmentation on pull-out and bending stiffness was strongly and negatively correlated to local bone density around the screw (correlation coefficient (R) = -0.95).

Conclusion

This combined experimental, µCT and µFE study showed that regional analyses may be sufficient to predict fixation strength in pull-out and that full analyses could show that cement augmentation around pedicle screws increased fixation stiffness in both pull-out and bending, especially for low-density bone.

Cite this article: Bone Joint Res 2021;10(12):797–806.

Proximal humeral fracture locking plate fixation with anatomic reduction, and a short-and-cemented-screws configuration, dramatically reduces the implant related failure rate in elderly patients

Background

Multiple studies have reported an unacceptable implant-related complication rate in proximal humeral fractures treated with locking plates, particularly in older patients. Our objective was to compare the fracture fixation failure rates in elderly patients, after a dedicated technique for locking plate fixation with cement augmentation or without it.

Methods

A total of 168 open reduction and internal fixation with locking plates were performed for complex proximal humerus fractures by a single surgeon in 136 women and 32 men older than 65 years of age (average 76 years). Treatment groups included group 1 with noncemented screws (n = 90) and group 2 with cemented screws (n = 78). As per Mayo-FJD Classification, there were 74 (44%) varus posteromedial impaction, 41 (24%) algus impaction, 46 (28%) surgical neck, and 7 (4%) head dislocation injuries. A retrospective radiographic and a clinical analysis was performed.

Results

At a mean follow-up of 33 months, the implant failure rate was significantly lower in the cement augmentation group (1% vs. 8%, P = .03). The overall complication rate was 21% (25% group 1, 15% group 2; P = .1). Global avascular necrosis was associated with sustaining a valgus impacted fracture (P = .02 odds ratio 5.7), but not to augmentation. Partial avascular necrosis occurred only in patients treated with cemented screws (3.8%). The overall revision rate was 9% in both groups. Forward elevation was 126 ± 36 degrees and external rotation was 44 ± 19 degrees. The mean Constant score was 70 ± 15 in group 1 and 76 ± 15 in group 2 (P = .03).

Conclusion

Cement augmentation significantly decreased the rate of implant failure. Good results are expected for most patients treated with this technique.

Multi-objective design optimization of dental implant geometrical parameters

In-silico investigations are becoming an integral part of the development of novel biomedical devices, including dental implants. Using computer simulations can streamline the process by tuning different geometrical and structural features, emphasizing the osseointegration of the implant design a priori, leading to the optimal designs in preparation for in-vivo trails. This research aims to elucidate the interrelationship between 12 geometrical variables that holistically define the shape of the implant. The approach to achieve optimality hinged on coupling the finite element analysis results with the fractional factorial design method. The latter was used to determine the most influential variables during the screening process, followed by the parameter optimization process using the response surface method, regarding four different objectives, namely: bone-implant contact area, volume of trabecular bone dead cells, volume of cortical bone dead cells, and axial displacement. This resulted in reducing the number of virtual experiments and substantially decreasing the computational cost without compromising the accuracy of the solution. It was found that the optimized values improved the performance significantly. The validity of all models was verified by comparing optimized responses with simulation results. A sensitivity analysis was performed on all five optimized models to address the effect of friction coefficient on the implant-bone joint interaction. It was shown that the mechanical behavior of implant-bone would be independent in higher friction coefficients. The significance of this study is demonstrated in determining the most effective and optimized values of all possible geometrical parameters considering their singular or interactive effects.

Finite Element Analysis of Fracture Fixation

PURPOSE OF REVIEW

Fracture fixation aims to provide stability and promote healing, but remains challenging in unstable and osteoporotic fractures with increased risk of construct failure and nonunion. The first part of this article reviews the clinical motivation behind finite element analysis of fracture fixation, its strengths and weaknesses, how models are developed and validated, and how outputs are typically interpreted. The second part reviews recent modeling studies of the femur and proximal humerus, areas with particular relevance to fragility fractures.

RECENT FINDINGS

There is some consensus in the literature around how certain modeling aspects are pragmatically formulated, including bone and implant geometries, meshing, material properties, interactions, and loads and boundary conditions. Studies most often focus on predicted implant stress, bone strain surrounding screws, or interfragmentary displacements. However, most models are not rigorously validated. With refined modeling methods, improved validation efforts, and large-scale systematic analyses, finite element analysis is poised to advance the understanding of fracture fixation failure, enable optimization of implant designs, and improve surgical guidance.