Medial sustainable nail versus proximal femoral nail antirotation in treating AO/OTA 31-A2.3 fractures: Finite element analysis and biomechanical evaluation

Biomechanical characteristic differences of two new types of intramedullary nail devices in the treatment of comminuted intertrochanteric fractures of femur: a comparative study based on finite element analysis

OBJECTIVE

Given the recent application of two new types of intramedullary nail devices in the treatment of comminuted femoral intertrochanteric fractures (CFIFs), there is still a lack of deep understanding and comparative evaluation of their biomechanical properties. Therefore, this study aims to systematically compare the advantages and disadvantages of these two new devices with traditional proximal femoral nail antirotation (PFNA) and InterTan nails in the fixation of CFIFs through finite element analysis.

METHODS

Based on the validated finite element model, this study constructed an accurate CFIFs model. In this model, PFNA, InterTan nails, proximal femoral bionic nails (PFBN), and new intramedullary systems (NIS) were implanted, totaling four groups of finite element models. Each group of models was subjected to simulation tests under a vertical load of 2100 N to evaluate the displacement and Von Mises stress (VMS) distribution of the femur and intramedullary nail devices.

RESULTS

Under a vertical load of 2100 N, a comparative analysis of the four finite element models showed that the NIS device exhibited the most superior performance in terms of peak displacement, while the PFNA device performed relatively poorly. Although the NIS device had the highest peak stress in the femur, it had the smallest peak displacement of both the femur and intramedullary nail devices, and the peak stress was mainly concentrated on the lateral side of the femur, with significantly lower stress in the proximal femur compared to the other three intramedullary nail devices. In contrast, the PFBN device had the lowest peak stress in the femur, and its peak displacement of both the femur and intramedullary nail devices was also less than that of PFNA and InterTan nails.

CONCLUSION

This study demonstrates that in the treatment of CFIFs, PFBN and NIS devices exhibit superior biomechanical performance compared to traditional PFNA and InterTan nail devices. Especially the NIS device, which can achieve good biomechanical results when fixing femoral intertrochanteric fractures with missing medial wall. Therefore, both PFBN and NIS devices can be considered reliable closed reduction and internal fixation techniques for the treatment of CFIFs, with potential clinical application value.

Finite element analysis of fixation stability according to reduction position for internal fixation of intertrochanteric fractures

In recent years, finite element analysis (FEA) has been instrumental in comparing the biomechanical stability of various implants for femur fracture treatment and in studying the advantages and disadvantages of different surgical techniques. This analysis has proven helpful for enhancing clinical treatment outcomes. Therefore, this study aimed to numerically analyze fixed stability according to location using FEA. In this study, a virtual finite element model was created based on a clinically anatomically reduced patient. It incorporated positive and negative support derived from intramedullary and extramedullary reduction from the anteroposterior (AP) view and neutral support from the lateral view. The generated model was analyzed to understand the biomechanical behavior occurring in each region under applied physiological loads. The simulation results of this study showed that the average von Mises stress (AVMS) of the nail when performing intramedullary reduction for femoral fixation was 187% of the anatomical reduction and 171% of the extramedullary reduction, and individually up to 2.5 times higher. In other words, intramedullary reduction had a very high possibility of fixation failure compared to other reduction methods. This risk is amplified significantly, especially in situations where bone strength is compromised due to factors such as old age or osteoporosis, which substantially affects the stability of fixation. Extramedullary reduction, when appropriately positioned, demonstrates greater stability than anatomical reduction. It exhibits stable fixation even in scenarios with diminished bone strength. In instances in which the bone density was low in the support position, as observed in the lateral view, the AVMS on the nail appeared to be relatively low, particularly in cases of positive support. Additionally, the femur experienced lower equivalent stress only in the extramedullary reduction-negative position. Moreover, by comparing different reduction methods and bone stiffness values using the same femoral shape, this study offers insights into the selection of appropriate reduction methods. These insights could significantly inform decision making regarding surgical strategies for intertrochanteric fractures.

Impact of blade direction on postoperative femoral head varus in PFNA fixed patients: a clinical review and biomechanical research

Intertrochanteric femur fracture is a common type of osteoporotic fracture in elderly patients, and postoperative femoral head varus following proximal femoral nail anti-rotation (PFNA) fixation is a crucial factor contributing to the deterioration of clinical outcomes. The cross-angle between the implant and bone might influence fixation stability. Although there is a wide range of adjustment in the direction of anti-rotation blades within the femoral neck, the impact of this direct variation on the risk of femoral head varus and its biomechanical mechanisms remain unexplored. In this study, we conducted a retrospective analysis of clinical data from 69 patients with PFNA fixation in our institution. We judge the direction of blade on the femoral neck in on the immediate postoperative lateral X-rays or intraoperative C-arm fluoroscopy, investigating its influence on the early postoperative risk of femoral head varus. p < 0.05 indicates significant results in both correlation and regression analyses. Simultaneously, a three-dimensional finite element model was constructed based on the Syn-Bone standard proximal femur outline, exploring the biomechanical mechanisms of the femoral neck-anti-rotation blade direction variation on the risk of this complication. The results indicated that ventral direction insertion of the anti-rotation blade is an independent risk factor for increased femoral head varus. Complementary biomechanical studies further confirmed that ventral angulation leads to loss of fixation stability and a decrease in fixation failure strength. Therefore, based on this study, it is recommended to avoid ventral directional insertion of the anti-rotation blade in PFNA operation or to adjust it in order to reduce the risk of femoral head varus biomechanically, especially in unstable fractures. This adjustment will help enhance clinical outcomes for patients.

Biomechanical evaluation of ortho-bridge system and proximal femoral nail antirotation in intertrochanteric fractures with lateral wall fracture based on finite element analysis

Background

The integrity of the lateral wall in femoral intertrochanteric fractures significantly impacts fracture stability and internal fixation. In this study, we compared the outcomes of treating intertrochanteric fractures with lateral wall involvement using the ortho-bridge system (OBS) combined with proximal femoral nail antirotation (PFNA) versus simple PFNA from a biomechanical perspective.

Methods

Finite-element models of femoral intertrochanteric fractures with lateral wall involvement were subjected to fixation with OBS combined with PFNA and simple PFNA. Von Mises stress measurements and corresponding displacement assessments for each component of the model, including the proximal femur and lateral wall, were used to evaluate the biomechanical effects of OBS fixation on bone and intramedullary nail stability.

Results

Using PFNA alone to fix intertrochanteric fractures with lateral wall involvement resulted in von Mises stress levels on the lateral wall exceeding safe stress tolerances for bone growth. OBS fixation significantly reduced stress on the lateral wall of the femur and minimized the stress on each part of the intramedullary nail, reducing the overall displacement.

Conclusion

In cases of intertrochanteric fractures with lateral wall involvement, PFNA fixation alone may compromise the biomechanical integrity of the lateral femoral wall, increasing the risk of postoperative complications. The addition of OBS to PFNA significantly reduces stress on the lateral femoral wall. Consequently, OBS should be considered for lateral wall fixation when managing intertrochanteric fractures combined with lateral wall fractures.

Changes in nail position and antirotation blade angles on the risk of femoral head varus in PFNA fixed patients: a clinical review and comprehensive biomechanical research

BACKGROUND

Femoral head varus triggers poor clinical prognosis in intertrochanteric fracture patients with proximal femoral nail antirotation (PFNA) fixation. Studies present that changes in nail position and screw insertion angles will affect fixation stability, but the biomechanical significance of these factors on the risk of femoral head varus has yet to be identified in PFNA fixed patients.

METHODS

Clinical data in PFNA fixed intertrochanteric fracture patients have been reviewed, the relative position of intermedullary nail has been judged in the instant postoperative lateral radiography. Regression analyses have been performed to identify the effect of this factor on femoral head varus. Corresponding biomechanical mechanism has been identified by numerical mechanical simulations.

RESULTS

A clinical review revealed that ventral side nail insertion can trigger higher risk of femoral head varus, corresponding numerical mechanical simulations also recorded poor fixation stability in models with ventral side nail insertion, and changes in the trajectory of anti-rotation blade will not obviously affect this tendency.

CONCLUSIONS

Ventral side insertion of intramedullary nail can trigger higher risk of femoral head varus in PFNA fixed patients by deteriorating the instant postoperative biomechanical environment, and changes in blade trajectory cannot change this tendency biomechanically. Therefore, this nail position should be adjusted to optimize patients' prognosis.

Risk of internal fixation treatment in intertrochanteric fracture based on different lateral femoral wall thickness: finite element analysis

OBJECTIVE

The thickness of the lateral femoral wall, which is an important indicator for evaluating the stability and integrity of intertrochanteric fractures, has been widely studied in recent years. However, as a typical representative of internal fixation treatment, there are few reports on the biomechanical comparison between PFNA and DHS + CS. This study focused primarily on the biomechanical effects of different lateral femoral wall thicknesses on two types of internal fixation through finite element analysis.

METHODS

We randomly recruited a healthy adult and collected his femoral CT data to establish a model of femoral intertrochanteric fracture with different lateral femoral wall thicknesses. Following PFNA and DHS + CS fixation, femoral models were simulated, and variations in stress and displacement of the internal fixation and femoral head were recorded under the same physiological load.

RESULTS

First, finite element mechanical analysis revealed that the stress and displacement of the internal fixation and femoral head were lower in the femoral model after PFNA fixation than in the DHS + CS model. Second, as the outer wall thickness decreased, the stress and deformation endured by both types of internal fixation gradually increased.

CONCLUSIONS

Finite element analysis determined that PFNA exhibits significantly better biomechanical stability than DHS + CS when subjected to varying lateral femoral wall thicknesses. Moreover, lateral femoral wall thickness substantially affects the stability of the two internal fixation biomechanical environments. When the thickness of the lateral femoral wall is too small, we do not recommend using extramedullary fixation because there is a significant risk of internal fixation fracture.

Extending the intermedullary nail will not reduce the potential risk of femoral head varus in PFNA patients biomechanically: a clinical review and corresponding numerical simulation

Femoral head varus is an important complication in intertrochanteric fracture patients treated with proximal femoral nail anti-rotation (PFNA) fixation. Theoretically, extending the length of the intramedullary nail could optimize fixation stability by lengthening the force arm. However, whether extending the nail length can optimize patient prognosis is unclear. In this study, a review of imaging data from intertrochanteric fracture patients with PFNA fixation was performed, and the length of the intramedullary nail in the femoral trunk and the distance between the lesser trochanter and the distal locking screw were measured. The femoral neck varus status was judged at the 6-month follow-up. The correlation coefficients between nail length and femoral neck varus angle were computed, and linear regression analysis was used to determine whether a change in nail length was an independent risk factor for femoral neck varus. Moreover, the biomechanical effects of different nail lengths on PFNA fixation stability and local stress distribution have also been verified by numerical mechanical simulations. Clinical review revealed that changes in nail length were not significantly correlated with femoral head varus and were also not an independent risk factor for this complication. In addition, only slight biomechanical changes can be observed in the numerical simulation results. Therefore, commonly used intramedullary nails should be able to meet the needs of PFNA-fixed patients, and additional procedures for longer nail insertion may be unnecessary.

Finite element analysis of a customized coronoid prosthesis for traumatic coronoid deficiency

BACKGROUND

Traumatic coronoid deficiency with persistent elbow instability is a challenging condition. Autologous bone graft reconstruction is often associated with a range of additional clinical problems and the outcome is often unpredictable. The purpose of this study was to design a prosthetic device that can reconstruct coronoid deficiency of any height and to evaluate its mechanical properties using finite element analysis.

MATERIALS AND METHODS

A customized coronoid prosthesis was designed based on image registration, automatic measurement, and computer-aided design. After pilot study and sample size calculation, image data collected from 6 patients who underwent bilateral complete upper extremity CT scans were reconstructed. The test was divided into 3 groups: coronoid intact, prosthesis and autograft. Regan-Morrey type II and autologous olecranon osteotomy models were established. The prosthesis and autogenous olecranon were assembled to the coronoid base. Stress was applied axially along the proximal humeral diaphysis and implant micromotion and contact mechanics of the humeroulnar joint were measured at 30°, 45°, 60° and 90° of joint flexion respectively.

RESULTS

At all flexion angles, the maximum stress on the coronoid articular surface was significantly reduced in the prosthesis and autograft groups, with the reduction being more significant in the latter (P < .001). With increasing flexion, the maximum stress at the coronoid articular surface increased significantly after autograft reconstruction (7.2 to 68 MPa, P < .001), whereas the humeroulnar joint obtained a similar contact mechanics pattern to that of the control group after prosthetic reconstruction. As the flexion angle increased, the relative micromotion of both the prosthesis and autograft increased significantly (0.5-1.6 vs. 0.2-1.2, Pmeasure time < 0.001, Pgroups < 0.001). Contact pressure and center-of-force paths of the humeroulnar joint experience abrupt stress changes at approximately 60° of flexion.

CONCLUSION

The contact stress pattern in the humeroulnar joint is similar in prosthesis and intact coronoid groups. Autograft reconstruction increases contact stresses at the articular surface and alters the joint center-of-force path. The "stress surge phenomenon" in the humeroulnar joint surface before and after 60° of flexion may be one of the mechanisms of traumatic elbow degeneration.

A probabilistic approach for assessing the mechanical performance of intertrochanteric fracture stabilized with proximal femoral nail antirotation

Maintaining post-operative mechanical stability is crucial for successfully healing intertrochanteric fractures treated with the Proximal Femoral Nail Antirotation (PFNA) system. This stability is primarily dependent on the bone mineral density (BMD) and strain on the fracture. Current PFNA failure analyses often overlook the uncertainties related to BMD and body weight (BW). Therefore, this study aimed to develop a probabilistic model using finite element modeling and engineering reliability analysis to assess the post-operative performance of PFNA under various physiological loading conditions. The model predictions were validated through a series of experimental test. The results revealed a negative nonlinear relationship between the BMD and compressive strain. Conversely, the BW was positively and linearly correlated with the compressive strain. Importantly, the compressive strain was more sensitive to BW than to BMD when the BMD exceeded 0.6 g/cm3. Potential trabecular bone compression failure is also indicated if BMD is equal to or below 0.15 g/cm3 and BW increases to approximately 2.5 times the normal or higher. This study emphasizes that variations in the BMD significantly affect the probability of failure of a PFNA system. Thus, careful planning of post-operative physical therapy is essential. For patients aged > 50 years restrictions on high-intensity activities are advised, while limiting strenuous movements is recommended for those aged > 65 years.

Biomechanical Research of Three Parallel Cannulated Compression Screws in Oblique Triangle Configuration for Fixation of Femoral Neck Unstable Fractures

OBJECTIVE

Surgical treatment with internal fixation, specifically percutaneous fixation with three cannulated compression screws (CCSs), is the preferred choice for young and middle-aged patients. The mechanical advantage of the optimal spatial configuration with three screws provides maximum dispersion and cortical support. We suspect that the spatial proportion of the oblique triangle configuration (OTC) in the cross-section of the femoral neck isthmus (FNI) may significantly improve shear and fatigue resistance of the fixed structure, thereby stabilizing the internal fixation system in femoral neck fracture (FNF). This study aims to explore the mechanical features of OTC and provide a mechanical basis for its clinical application.

METHODS

Twenty Sawbone femurs were prepared as Pauwels type III FNF models and divided equally into two fixation groups: OTC and inverted equilateral triangle configuration (IETC). Three 7.3 mm diameter cannulated compression screws (CCSs) were used for fixation. The specimens of FNF after screw internal fixation were subjected to static loading and cyclic loading tests, respectively, with five specimens for each test. Axial stiffness, 5 mm failure load, ultimate load, shear displacement, and frontal rotational angle of two fragments were evaluated. In the cyclic loading test, the load sizes were 700 N, 1400 N, and 2100 N, respectively, and the fracture end displacement was recorded. Results were presented as means ± SD. Data with normal distributions were compared by the Student's t test.

RESULTS

In the static loading test, the axial stiffness, ultimate load, shear displacement, and frontal rotational angle of two fragments were (738.64 vs. 620.74) N/mm, (2957.61 vs. 2643.06) N, (4.67 vs. 5.39) mm, and (4.01 vs. 5.52)° (p < 0.05), respectively. Comparison between the femoral head displacement after 10,000 cycles of 700N cyclic loading and total displacement after 20,000 cycles of 700-1400N cyclic loading showed the OTC group was less than the IETC group (p < 0.05). A comparison of femoral head displacement after 10,000 cycles of 1400N and 2100N cycles and total displacement after 30,000 cycles of 700-2100N cycles showed the OTC group was less than another group, but the difference was not significant (p > 0.05).

CONCLUSION

When three CCSs are inserted in parallel to fix FNF, the OTC of three screws has obvious biomechanical advantages, especially in shear resistance and early postoperative weight-bearing, which provides a mechanical basis for clinical selection of ideal spatial configuration for unstable FNF.

Increasing the angle between caudal screw and the transverse plane may aggravate the risk of femoral head necrosis by deteriorating the fixation stability in patients with femoral neck fracture

Necrosis of the femoral head is the main complication in femoral neck fracture patients with triangle cannulated screw fixation. Instant postoperative fixation instability is a main reason for the higher risk of femoral head necrosis. Biomechanical studies have shown that cross screw fixation can effectively optimize fixation stability in patients with proximal humerus fractures and pedicle screw fixation, but whether this method can also effectively optimize the fixation stability of femoral neck fractures and reduce the corresponding risk of femoral head necrosis has yet to be identified. In this study, a retrospective review of imaging data in femoral neck fracture patients was performed. The cross angle between the femoral neck and the caudal cannulated screw was reported; if the angle between the screw and the transverse plane increased, it was recorded as positive; otherwise, it was recorded as negative. Angle values and their corresponding absolute values were compared in patients with and without femoral head necrosis. Regression analysis identified potential risk factors for femoral head necrosis. Moreover, the biomechanical effect of the screw-femoral neck angle on fixation stability was also verified by numerical mechanical simulations. Clinical review presented significantly larger positive angle values in patients with femoral head necrosis, which was also proven to be an independent risk factor for this complication. Moreover, fixation stability progressively deteriorated with increasing angle between the caudal screw and the transverse plane. Therefore, increasing the angle between the caudal screw and the transverse plane may aggravate the risk of femoral head necrosis by deteriorating the fixation stability in patients with femoral neck fracture.

Finite element analysis and a pilot study of different fixation constructs for Danis-Weber A and B lateral malleolus fractures

BACKGROUND

Displaced lateral malleolus fractures are typically stabilised through open reduction and internal fixation. The biomechanically and clinically efficacy of locking plates and lag screws, particularly in Weber A and B distal fibular fractures remains a subject of contention. This study examines two locking plate designs for lateral malleolus fractures, evaluating their performance with and without interfragmentary screws using finite element models.

METHODS

Utilising CT images of a healthy adult male volunteer, a three-dimensional finite element model was constructed. The Fibula-specific Flank Multiaxial Locking Anatomic Plate (FMLP) and the Conventional Locking Plate (CLP) were subjected to stabilisation, both with and without an interfragmentary screw, mimicking the Danis-Weber A and B lateral malleolus oblique fracture fixation. Loads of 140 N and 70 N, equivalent to 20% of the body weight, were applied to simulate the single-leg and two-leg standing conditions in the axial direction. The von Mises stress (VMS) distributions and element displacements were subsequently analyzed.

RESULTS

In the Danis-Weber A fracture model group, the FMLP with an interfragmentary screw fixation exhibited the lowest peak VMS values: 51.9 MPa in the fibula, 89.0 MPa in the plate, and 61.3 MPa in the screws for simulating single-leg conditions. Under two-leg standing conditions, these peak VMS values decreased to 25.9 MPa in the fibula, 44.5 MPa in the plate, and 30.6 MPa in the screws, respectively. Furthermore, the overall structural peak displacements during single-leg standing for both Weber-A and B fractures with different implants ranged from 1.61 to 2.54 mm. While standing on two feet, the ranged was from 0.80 to 1.27 mm. An interfragmentary screw at the oblique fracture site resulted in reduced the peak value of VMS in the fibula, plate, screws, consequently decreased the overall structural displacement for FMLP and CLP fixation in lateral malleolus fractures.

CONCLUSIONS

The current finite element analysis (FEA) demonstrates that FMLP exhibits superior mechanical characteristics in Danis-Weber A and B lateral malleolus fractures compared to CLP. The inclusion of an interfragmentary screw, combined with locking plate design, enhances stability for simple oblique distal fibular fractures. The FMLP presents itself as potential as an alternative for lateral malleolus fractures from a biomechanical perspective. Nevertheless, further verification of these results is imperative through subsequent clinical studies.

A novel intramedullary nail design of intertrochanteric fracture fixation improved by proximal femoral nail antirotation

A proper and reliable fracture fixation is important for fracture healing. The proximal femoral intramedullary nail (IN), such as proximal femoral nail anti-rotation (PFNA) or Gamma nail, is widely used for intertrochanteric fracture fixation. However, it still suffers considerable stress concentrations, especially at the junction between the nail and the blade or lag screw. In this study, we propose a novel intramedullary nail design to enhance the intramedullary nail integrity by introducing a bolt screw to form a stable triangular structure composed of the nail, the lag screw, and the bolt screw (PFTN, Proximal femoral triangle nail). Systematic finite element numerical simulations were carried out to compare the biomechanical performances of PFTN and PFNA under both static and dynamic loads during the postures of ascending and descending stairs. The simulation results highlight the advantages of the proposed PFTN design with lower stresses, less stress concentration, and higher structure stability.

Biomechanical evaluation of three implants for treating unstable femoral intertrochanteric fractures: finite element analysis in axial, bending and torsion loads

Purpose: How to effectively enhance the mechanical stability of intramedullary implants for unstable femoral intertrochanteric fractures (UFIFs) is challenging. The authors developed a new implant for managing such patients. Our aim was to enhance the whole mechanical stability of internal devices through increasing antirotation and medial support. We expected to reduce stress concentration in implants. Each implant was compared to proximal femoral nail antirotation (PFNA) via finite element method. Methods: Adult AO/OTA 31-A2.3 fracture models were constructed, and then the new intramedullary system (NIS), PFNA, InterTan nail models were assembled. We simulated three different kinds of load cases, including axial, bending, and torsion loads. For further comparison of PFNA and the NIS, finite element analysis (FEA) was repeated for five times under axial loads of 2100 N. Two types of displacement and stress distribution were assessed. Results: Findings showed that the NIS had the best mechanical stability under axial, bending, and torsion load conditions compared to PFNA and InterTan. It could be seen that the NIS displayed the best properties with respect to maximal displacement while PFNA showed the worst properties for the same parameter in axial loads of 2100 N. In terms of maximal stress, also the NIS exhibited the best properties while PFNA showed the worst properties in axial loads of 2100 N. For bending and torsion load cases, it displayed a similar trend with that of axial loads. Moreover, under axial loads of 2100 N, the difference between the PFNA group and the NIS group was statistically significant (p < 0.05). Conclusion: The new intramedullary system exhibited more uniform stress distribution and better biomechanical properties compared to the PFNA and InterTan. This might provide a new and efficacious device for managing unstable femoral intertrochanteric fractures.

The importance of the thickness of femoral lateral wall for treating intertrochanteric fractures: a finite elements analysis

To explore how the thickness of the femoral lateral wall influences the effectiveness of internal fixation systems used to treat intertrochanteric fractures. CT images of the pelvis and femur of a male adult were used to construct an intertrochanteric fracture model (AO/OTA 31-A2) with various thicknesses of the femoral lateral wall (FLW). Four finite element (FE) models were created with the lateral femoral walls being 10 mm, 20 mm, 30 mm, and 40 mm thick. The fracture models were fixed with a dynamic hip screw (DHS), a proximal femoral nail anti-rotation (PFNA), and a proximal femoral locking compression plate (P-FLCP). A simulated vertical load was applied to the femoral head. The stress and displacement of the implant and femur in each model were recorded for comparison. The FE analysis of the intertrochanteric fracture models showed that the PFNA system could provide better stability than the DHS and P-FLCP with the same thickness of FLW. The FLW provided buttress support to the femoral head and neck when using a DHS and PFNA, and the buttress strength was proportional to the thickness of FLW. The maximum stress in the DHS model was recorded on the DHS plate which accommodated the lag screw. For the PFNA model, the maximum stress appeared at the connection between the nail and blade. In the P-FLCP model, the maximum stresses were highly concentrated at the connection between the cephalic nails and the proximal plate. The thickness of the femoral lateral wall should be considered an important factor when selecting a suitable internal fixation system for intertrochanteric fractures. Based on the FE analysis, intramedullary fixation, such as PFNA, experiences lower stress levels and a moderate displacement in comparison to DHS and P-FCLP when used to treat intertrochanteric fractures.

Mechanical comparison of standard interlocking, clawed, and expandable wedge locked nail fixations: An experimental and numerical study

INTRODUCTION

Intramedullary nailing has been used as a standard in the treatment of the long bone fractures with its clinical and mechanical advantages. However, using distal locking screws has been associated with longer operative times, higher radiation exposure rates, and complications like breakages of distal screw or nail at the screw hole level. Therefore, attempts to eliminate distal locking screws has been always present for intramedullary nail fixation. With a similar purpose, the present study has been carried out to compare mechanical behaviors of intramedullary nail fixations with different distal locking elements.

MATERIALS AND METHODS

In this study, mechanical behaviors of standard interlocking and clawed nail fixations were compared experimentally in the first part. Six fourth generation Sawbones femurs, which have a simulated subtrochanteric fracture, were divided equally and were fixed with standard interlocking and clawed nails. During axial compression tests, experimental strain measurements were taken from all fixations. After validation of numerical models with using experimental strains and stiffnesses, mechanical behaviors of standard interlocking, clawed, and wedge locked nail fixations were compared numerically under axial compression loads. In numerical comparison, the stress-strain distributions were evaluated.

RESULTS

Experimental results showed that although that there was no significant difference in stiffnesses, standard nail fixation bore two times higher loads than clawed nail fixations. Under loading, decrease in the distance between fracture surfaces was approximately seven times higher in the clawed nail fixation when compared to standard nail fixations. Numerical results showed that wedge locked nail fixation provided equivalent mechanical behavior to standard interlocking nail.

DISCUSSION

In experiments of clawed nail fixation, the high decrease in the distance between fracture surfaces was evidence of the slippage of nail in the medullary canal. For a safe fixation, claws should be deployed when they are completely in contact with the cortical bone, they should be stuck into the bone in a fair amount, and the deployment in the distal third of the femur should be avoided. According to experimentally validated numerical analyses, wedge locked nail fixation may be an alternative for standard interlocking nail fixation if experimental studies support the present results.

Prediction of osteoporosis from proximal femoral cortical bone thickness and Hounsfield unit value with clinical significance

Background

Utilizing dual-energy x-ray absorptiometry (DXA) to assess bone mineral density (BMD) was not routine in many clinical scenarios, leading to missed diagnoses of osteoporosis. The objective of this study is to obtain effective parameters from hip computer tomography (CT) to screen patients with osteoporosis and predict their clinical outcomes.

Methods

A total of 375 patients with hip CT scans for intertrochanteric fracture were included. Among them, 56 patients possessed the data of both hip CT scans and DXA and were settled as a training group. The cortical bone thickness (CTh) and Hounsfield unit (HU) values were abstracted from 31 regions of interest (ROIs) of the proximal femur. In the training group, the correlations between these parameters and BMD were investigated, and their diagnostic efficiency of osteoporosis was assessed. Finally, 375 patients were divided into osteoporotic and nonosteoporotic groups based on the optimal cut-off values, and the clinical difference between subgroups was evaluated.

Results

The CTh value of ROI 21 and the HU value of ROI 14 were moderately correlated with the hip BMD [r = 0.475 and 0.445 (p < 0.001), respectively]. The best diagnostic effect could be obtained by defining osteoporosis as CTh value < 3.19 mm in ROI 21 or HU value < 424.97 HU in ROI 14, with accuracies of 0.821 and 0.883, sensitivities of 84% and 76%, and specificities of 71% and 87%, respectively. The clinical outcome of the nonosteoporotic group was better than that of the osteoporotic group regardless of the division criteria.

Conclusion

The CTh and HU values of specific cortex sites in the proximal femur were positively correlated with BMD of DXA at the hip. Thresholds for osteoporosis based on CTh and HU values could be utilized to screen osteoporosis and predict clinical outcomes.

Optimizing fixation methods for stable and unstable intertrochanteric hip fractures treated with sliding hip screw or cephalomedullary nailing: A comparative biomechanical and finite element analysis study

BACKGROUND

Despite recent advances in implants and surgical techniques, catastrophic and clinical failures in the treatment of intertrochanteric fractures continue to occur, with dire consequences in an overall frail population subset. The aim of the current study is to evaluate the effect of the factors under the surgeons' control, namely fracture reduction and implant selection, on the biomechanical behavior of fracture fixation constructs.

MATERIAL-METHODS

An experimental protocol was conducted with the use of instrumented sawbones, in order to validate the finite element models. The implants used were the Gamma3®and DHS systems. Subsequently, a series of scenaria were considered, including various reduction and implant angle combinations. Data were retrieved concerning the peak cancellous bone stresses around the hip screw and the volume of cancellous bone in the femoral head stressed at critical levels, as well as implant stresses and stresses on the cortical bone of the distal fragment.

RESULTS

All stable fracture models displayed significantly decreased cancellous bone stresses and implant stresses compared to their unstable counterparts, regardless of implant used. The effect of increasing implant angle led to a decrease in implant stresses in all models studied, but had a beneficial effect on the stresses in the cancellous bone of the proximal fragment only in the subgroups of stable fractures with both implants and unstable fractures treated with a cephalomedullary nail (CMN). In unstable fractures anatomically reduced, the use of CMN led to significantly lower peak stresses in the cancellous bone and a smaller volume of bone stressed at critical levels. Increasing the reduction angle by 5 ° led to a significant decrease in both peak stresses and volume of bone stressed at critical levels, more prominent in the sliding hip screw (SHS) models. Decreasing the reduction angle into varus by 5 or 10 ° led to a significant increase in bone and implant stresses regardless of implant used.

CONCLUSIONS

In stable two-part (AO31.A2) fractures the use of the SHS appears to be biomechanically equivalent to CMN. In unstable, anatomically reduced fractures, the use of CMN leads to significantly reduced cancellous bone stresses and decreased rotation of the proximal fragment during loading. A reduction in varus should be avoided at all costs. In unstable fractures treated with SHS a reduction in slight valgus appears to be biomechanically beneficial. The highest implant angle that allows for proper screw position and trajectory in the femoral head should be used for stable fractures with both implants and unstable fractures treated with Gamma3®.

What is the most fixable intramedullary implant for basicervical fracture and transcervical shear fracture? - A finite element study

Objective

The objectives of this study are 1) to biomechanically compare six different intramedullary fixations for basicervical fracture (AO 31-B3, Type 2 in area classification) and transcervical shear fracture (AO 31-B2.3, Type 1-2 in area classification) using the finite element (FE) method, and 2) to investigate the effects of two different unstable fracture types on fixation.

Methods

FE models of two different types of proximal femoral fractures are constructed from CT scan images of a patient with osteoporosis. The fracture models are fixed with a short femoral nail with a single lag screw, short femoral nail with a single blade, and short femoral nail with double lag screws, and then fixed with long femoral nails for each of the three nail types. Subsequently, the maximum loads during walking and stair climbing, as well as the minimum principal strain and compressive failure elements are calculated to assess the fixation of each implant.

Results

In both fracture types, the long nail with double lag screws show the smallest volume of compressive failure elements (basicervical fracture, 2 mm3; transcervical shear fracture, 217 mm3). In all types of implants, the volume of the compressive failure elements is larger in the transcervical shear fracture than in the basicervical fracture. A similar trend is observed for the minimum principal strain (compressive strain).

Conclusion

The present study shows that a long nail with double lag screws is the most fixative intramedullary nail device for basicervical fracture and transcervical shear fracture in any condition. Furthermore, it is shown that transcervical shear fracture is considerably more unstable than basicervical fracture.

Improve biomechanical stability using intramedullary nails with femoral neck protection in femoral shaft fractures

BACKGROUND AND OBJECTIVE

Elderly patients treated for femoral shaft fractures have a higher risk of hip fracture. We hypothesized that intramedullary nails protecting the femoral neck can improve mechanical strength and reduce the risk of subsequent hip fracture. This study aims to analyze the biomechanical stability using intramedullary nails with or without femoral neck protection through finite element analysis.

METHODS

Thirty finite element models (FEMs) were established, including five different conditions of femoral shaft fracture: Fracture healing, Proximal fractures (Transverse and oblique), Distal fractures (Transverse and oblique), and five different fixation methods. Femoral neck protection groups: cephalomedullary nail (CN), reconstruction nail (RN); No femoral neck protection groups: type-1 of antegrade intramedullary nail (AIN-1), type-2 of antegrade intramedullary nail (AIN-2), and retrograde intramedullary nail (RIN). The maximum stress of bone and internal fixation in the femoral neck region for all type of fixation were calculated to evaluate the biomechanical stability.

RESULTS

Maximum equivalent stress values of bone in the femoral neck region for five different conditions of femoral shaft fracture: AIN-2 (77.23 MPa) >RIN (77.15 MPa) > AIN-1 (76.71 MPa) > CN (60.74 MPa) > RN (57.66 MPa) for the fracture healing; RIN (80.05 MPa) > AIN-1 (79.15 MPa) > AIN-2(78.77 MPa) > RN (65.16 MPa) > CN (65.03 MPa) for the proximal transverse fracture; RIN (80.10 MPa) > AIN-2 (79.36 MPa) > AIN-1 (79.18 MPa) > RN (65.09 MPa) > CN (64.96 MPa) for the proximal oblique fracture; RIN (80.24 MPa) > AIN-2 (79.68 MPa) > AIN-1 (79.33 MPa) > CN (65.02 MPa) > RN (64.76 MPa) for the distal transverse fracture; RIN (80.23 MPa) > AIN-2 (79.61 MPa) > AIN-1 (79.35 MPa) > CN (65.06 MPa) > RN (64.76 MPa) for the distal oblique fracture. Maximum equivalent stress of internal fixation in the femoral neck region is greater than the maximum stress of bone and avoids stress concentration of bone for the femoral neck protection groups (CN and RN).

CONCLUSIONS

Intramedullary nails with femoral neck protection in the treatment of femoral shaft fractures improve mechanical strength and prevent secondary hip fractures and decrease the overall risk of reoperation postoperatively.

Triangular Mechanical Structure of the Proximal Femur

Objective

The mechanical high modulus structure of the proximal femur could guide clinical surgical treatment and instrument design of proximal femoral fractures. The purpose of this study is to analyze and verify the mechanical structure of the proximal femur.

Methods

A total of 375 patients with intertrochanteric fractures were imaged using computed tomography (CT) scans. Patients were grouped according to age and sex. Cortical and medullary cavity parameters (cortical thickness [CTh], cortical mean density [CM], upper‐lower diameter length [ULL], and medial‐lateral diameter length [MLL]) were measured at eight planes. Six proximal femoral finite element models of different sexes and ages were constructed. To verify the measurement results, Abaqus was used to implement the force load to describe the von Mises stress distribution, and the maximum von Mises stress values of each wall of the proximal femur were compared.

Results

The CTh values of the lower and upper walls were higher than those of the anterior and posterior walls of the femoral neck (p < 0.05). The CM values of the lower and upper walls were higher than those of the anterior and posterior walls of the subcephalic and middle femoral neck (p < 0.05). The ULL value gradually increased from the subcephalic region to the bottom (p < 0.05). The CTh and CM values of the medial and lateral walls were higher than those of the anterior and posterior walls in the femoral trochanteric region (p < 0.05). The MLL value decreased gradually from the plane 20 mm above the upper edge to that 20 mm below the vertex of the femoral lesser trochanter (p < 0.05). The von Mises stress was concentrated on the upper and lower walls of the femoral neck and on the medial and lateral walls of the femoral trochanteric region. The maximum von Mises stress values of the upper and lower walls were higher than those of the anterior and posterior walls of the femoral neck. The maximum von Mises stress values of the medial and lateral walls were higher than those of the anterior and posterior walls in the femoral trochanteric region, except for the plane 20 mm above the upper edge of the femoral lesser trochanter.

Conclusion

The bone mass of the proximal femur presented a triangular high‐modulus distribution, which bore the main stress of the proximal femur. The triangular mechanical structure provides a guideline for the surgical strategy and instrument design of the proximal femur.

Finite-Element Analysis of a Novel Cephalomedullary Nail for Restricted Sliding to Reduce Risk of Implant Failure in Unstable Intertrochanteric Fractures

Objective

How to restrict sliding of cephalomedullary nail and rigid reconstruct medial support for unstable intertrochanteric fractures remains a challenge. This study aims to explore the feasibility of a novel cephalomedullary nail for restriction sliding and reconstruction of medial femoral support to prevent failure in unstable trochanteric fractures through finite element analysis.

Methods

The DICOM files of a unilateral femur spiral computed tomography (CT) scans from a elderly female were converted into STL files, and the most common clinical trochanteric fracture model with the absence of medial support, AO/OTA 31‐A2.3 was simulated by removing the posterior medial femur. The model of a novel medial sustain nail (MSN‐II) and a widely used nail (proximal femoral nail anti‐rotation PFNA‐II) were modeled according to the manufacturer‐provided engineering drawing. Different loads were applied to the femoral head to simulate the postoperative weight bearing gait. The sliding distance of helical blade in femoral neck, maximum stress of femur and nail, displacement of proximal fragment were analyzed to revealing the mechanical stability of unstable trochanteric fracture stabilized by different implant.

Results

The sliding distance of helical blade in the femoral neck, the maximum stress on the femur and nail, the displacement of proximal fragment in MSN‐II under 2100N axial load were 0.65 mm, 689 MPa, 1271 MPa, 16.84 mm respectively, while that were 1.43 mm, 720.8 MPa, 1444 MPa, 18.18 mm, respectively in PFNA‐II. The difference between the two groups was statistically significant (P < 0.05) and the stress was mainly distributed in medial distal side of nail but helical blade and the proximal aperture for the nail in MSN‐II. Compared to PFNA‐II, MSN‐II demonstrates biomechanical merit against femur medialization, cut‐out and coax varus.

Conclusion

The sliding distance of helical blade in femoral neck, the maximum stress on the femur and nail, and the displacement of proximal fragment of MSN‐II were less than those of PFNA‐II in the treatment of unstable intertrochanteric fractures. Therefore MSN‐II has better stability than PFNA‐II and it may have the potential to avoid femur medialization and cut out. It might be an option in unstable trochanteric fracture because of its superiority in restricted sliding and medial support reconstruction.

Finite Element Analysis of Proximal Femur Bionic Nail (PFBN) Compared with Proximal Femoral Nail Antirotation and InterTan in Treatment of Intertrochanteric Fractures

Objective

To compare the biomechanical properties of proximal femur bionic nail (PFBN), proximal femoral nail antirotation (PFNA) and InterTan in the treatment of elderly intertrochanteric fractures AO/OTA 31‐A1.3 by finite element analysis.

Methods

We used Mimics, Unigraphics and other software to establish normal femur and AO/OTA 31‐A1.3 fracture models, and reconstructed PFBN, PFNA and InterTan intramedullary nail models, and assembled them on the fracture model. The ANSYS software was used to compare the femoral von Mises stress distribution, deformation distribution, and internal fixation stress distribution of each group under a load of 2100 N.

Results

It could be seen that the femoral maximum stress, femoral maximum displacement, and maximum stress of internal fixation of the PFBN group were lower than those in the PFNA group and the InterTan group. The maximum femoral stress of the PFBN was 190.25 MPa, while the maximum stress of the femur of the PFNA and InterTan groups were 238.41 Mpa and 226.97 Mpa. The maximum femoral displacement of each group were located at the top of the femoral head, and the maximum displacement of the PFBN group was 14.373 mm, and the maximum displacement values of the PFNA and InterTan groups were 19.49 and 15.225 mm. For the stress distribution of intramedullary nail, the maximum stress of the three kinds of internal fixation was located on the main nail. The maximum stress of PFBN was 1191.8 MPa, compared with 2142.8 MPa for PFNA and 1702.3 MPa for InterTan. And the maximum stress on the PFBN pressure nail was 345.35 MPa, compared with 868.6 MPa for the PFNA spiral blade and 545.5 MPa for InterTan interlocking twin nails.

Conclusion

Compared with PFNA and InterTan, PFBN has better mechanical properties. The biomechanical characteristics of PFBN are more advantageous than PFNA and InterTan internal fixation system in the treatment of femoral intertrochanteric fractures.

Spatial Bridge Locking Fixator versus Traditional Locking Plates in Treating AO/OTA 32-A3.2 Fracture: Finite Element Analysis and Biomechanical Evaluation

Objective

To compare the biomechanical behaviors of the spatial bridge locking fixator (SBLF), single locking plate (SP), and double locking plate (DP) for AO/OTA 32‐A3.2 fractures using finite element analysis and biomechanical tests.

Methods

Axial loading of 700 N was conducted on the AO/OTA 32‐A3.2 model via finite element analysis. The von Mises stress and the interfragmentary movement (IFM) were comparatively analyzed in the three configurations above. On the mechanical tester, axial and torsional loading of 30 synthetic femurs (five specimens of each configuration for each test at random) was performed, and the interfragmentary movement, torsion angle, stiffness, and ultimate load were recorded and analyzed.

Results

The finite element analysis (FEA) results showed that the von Mises stress of the spatial bridge locking fixator (SBLF) was lower than that of the single locking plate (SP) and higher than that of the double locking plate (DP). At 700 N, the axial IFMs were 0.15–0.38 mm (SBLF), 0.03–0.84 mm (SP), and 0.02–0.07 mm (DP). The biomechanical experiment indicated that the axial interfragmentary movements (IFMs) were 0.44 ± 0.23 mm (SBLF), 1.02 ± 0.40 mm (SP), and 0.07 ± 0.07 mm (DP) (p < 0.001). The axial IFM of the SBLF group had the highest probability (79.26%) of falling within the ideal range (0.2–0.8 mm), and the SP and DP groups had probabilities of 27.10% and 3.14%, respectively. The axial stiffness in the SBLF group (1586 ± 130 N/mm) was significantly lower than that in the DP group (10,264 ± 2671 N/mm) (p < 0.001) but greater than that in the SP group (725 ± 178 N/mm) (p = 0.396). The range of axial loads to ultimate failure was 3385–4527 N (SBLF), 3377–4664 N (SP), and 3780–4804 N (DP). The shear motion of the fracture end was 0.35 ± 0.14 mm (SBLF), 0.16 ± 0.10 mm (SP), and 0.08 ± 0.04 mm (DP) (p < 0.001). The torsional stiffness was 1.68 ± 0.14 Nm/degree (SBLF), 2.32 ± 0.29 Nm/degree (SP) (SBLF&SP, p < 0.001), and 3.53 ± 0.73 Nm/degree (DP) (SBLF&DP, p < 0.001).

Conclusions

The SBLF structure may exhibit a better biomechanical performance compared with the SP and DP in providing the best quantity and more symmetrical interfragmentary movement for AO/OTA 32‐A3.2 fractures.

A rare complication of pelvic perforation by an excessive medial slide of the helical blade after treatment of an intertrochanteric fracture with proximal femoral nail anti-rotation: A case report and literature review

Intertrochanteric fractures have become a severe public health problem in elderly patients. Proximal femoral nail anti-rotation (PFNA) is a commonly used intramedullary fixation device for unstable intertrochanteric fractures. Pelvic perforation by cephalic screw is a rare complication. We reported an 84-year-old female who fell at home and sustained an intertrochanteric fracture. The patient underwent surgery with PFNA as the intramedullary fixation device. Routine postoperative examination revealed medial migration of the helical blade that eventually caused pelvic perforation. We performed a cemented total hip arthroplasty as the savage procedure. At the latest follow-up of 12 months after total hip arthroplasty, the patient had no pain or loosening of the prosthesis in the left hip. Pelvic perforation should be considered when choosing PFNA as the intramedullary fixation device, especially in patients with severe osteoporosis wherein the helical blade can be easily inserted during the operation. The lack of devices to avoid oversliding of the helical blade in PFNA is an unreported cause of this complication and should be considered in such cases.

Cement augmentation of the proximal femoral nail antirotation for the treatment of two intertrochanteric fractures - a comparative finite element study

BACKGROUND

There are concerns regarding initial stability and cutout effect in proximal femoral nail antirotation (PFNA) treating intertrochanteric fractures. No study have used finite element analysis (FEA) to investigate the biomechanics. This study aimed to compare the cutout effect, stress and displacement between stable (AO31-A1.3) and unstable (AO31-A2.2) intertrochanteric fractures treated by cement augmented PFNA.

METHODS

Four femoral finite element models (FEMs) were constructed and tested under the maximum loading during walking. Non-augmented and augmented PFNA in two different intertrochanteric fractures were respectively simulated, assuming Tip Apex Distance (TAD) < 25 mm within each FEM. The cutout effect, stress and displacement between femur and PFNA were compared in each condition.

RESULTS

Cutout effect was observed in both non-augmented femoral head and was more apparently in unstable intertrochanteric fracture model. After reinforced by bone cement, no cutout effect occurred in two models. Stress concentration were observed on medial part of intertrochanteric region and the proximal part of helical blade before augmented while were observed on femoral shaft and the conjunction between blade and nail after augmented in both FEMs. Displacement mainly appeared on femoral head and the helical blade tip before augmented while distributed moderately on intertrochanteric region and the upper part of nail after augmented in both FEMs. The maximum stress and displacement value of femur decreased both in stable and unstable model after augmented but was more significantly in the unstable one. The maximum stress and displacement value of PFNA increased both in stable and unstable model after augmented but was more significantly in the unstable one.

CONCLUSION

Our FEA study indicated that the cement augmentation of the PFNA biomechanically enhances the cutout resistance in intertrochanteric fracture, this procedure is especially efficient for the unstable intertrochanteric fracture.

Numerical evaluation of the mechanical properties of a novel expandable intramedullary nailing: A new alternative to standard interlocking nailing

INTRODUCTION

There has been a great effort in preventing the disadvantages of distal locking in intramedullary nailing to date. From this scope, a novel expandable nail fixation eliminating distal locking screws has been designed. The primary aim of this numerical parametric study is to investigate mechanical behavior of expandable nail fixation on the fractured femur model under different contact parameters which are effective in maintaining the nail position and to specify the appropriate values of these contact parameters for a safe fixation. The second aim is to compare mechanical behavior of the expandable nail fixation with the standard interlocking nail fixation.

MATERIALS AND METHODS

The expandable nail has three wedges which are responsible for distal fixation by compressing the medullary canal in the radial direction. 4th generation Sawbones femur model was used as bone model. A transverse osteotomy with 20 mm gap was created to simulate a subtrochanteric fracture. The fixations have been examined under axial compression with 1200 N and torsion with 7 Nm. In the parametric study, the tightening torque and static friction coefficient in wedge-canal contact were selected as contact parameters. The outputs were stiffnesses of the fixations, equivalent von-Mises stress distribution on the models, and load sharing between the canal and distal locking elements.

RESULTS

The results of the parametric study showed that the model with the tightening torque of 3 Nm and friction coefficient of 0.7 was the safest. The load borne by wedges is generally prone to increase with increased tightening torque and friction coefficient. The both fixations showed close stiffness and stress values.

CONCLUSION

The tightening torque of the wedge locking mechanism is directly effective in maintaining the nail position constant in canal, and the safety of the fixation is better ensured with increased tightening torque but stress states on bone must be carefully evaluated. The expandable nail provided comparable results to standard interlocking nails with respect to the fixation stiffness, stress, and contact forces. The expandable nailing may be evaluated as an alternative in the fractures of long bones in the case that the numerical results are supported by future experimental studies.

Risk of proximal femoral nail antirotation (PFNA) implant failure upon different lateral femoral wall thickness in intertrochanteric fracture: a finite element analysis

Proximal Femoral Nail Antirotation (PFNA) has been commonly used to treat intertrochanteric fractures, despite the risk of implant failure. The integrity of the femur could influence the risk of implant failure. This study evaluated the influence of lateral femoral wall thickness on the potential of implant failure. A finite element model of the hip was reconstructed from the Computed Tomography of a female patient. Five intertrochanteric fracture models at different lateral femoral wall thickness (T1 = 27.6 mm, T2 = 25.4 mm, T3 = 23.4 mm, T4 = 21.4 mm, and T5 = 19.3 mm) were then created and fixed with PFNA. We simulated a critical loading condition by a high loading case during walking. Elastoplastic material models with yield stress and failure strain were applied to the bone and implant in which breakage can be simulated using the element deletion function. In addition, the stress and displacement of the implant and femur were analysed. Implant breakage occurred at the sides of the proximal nail canal in cases of T4 and T5 which was further supported by the higher maximum von Mises stress and nail displacement. The increased stress and displacement of the implant may implicate a reduction of stability and risk of implant failure. We suggested that precaution shall be taken when the wall thickness was less than 21.4 mm.

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.

Positive or negative anteromedial cortical support of unstable pertrochanteric femoral fractures: A finite element analysis study

OBJECTIVE

To explore the mechanical stability of unstable pertrochanteric fractures with proximal femoral nail anti-rotation (PFNA-Ⅱ) fixation under different anteromedial cortical support reduction patterns.

METHODS

A 65-year-old healthy male volunteer with no history of hip or systemic disease was recruited. High-resolution computed tomography images with a slice thickness of 0.67 mm of his right femur were obtained. These images were used to establish three-dimensional (3D) models. The lesser trochanter and lateral femoral wall were cut off to create an AO Foundation/Orthopaedic Trauma Association type 31-A2 unstable pertrochanteric fracture model. PFNA-Ⅱ was used to simulate fixation. Nine different fracture reduction patterns, which included positive-positive, positive-neutral, positive-negative, neutral-positive, neutral-neutral, neutral-negative, negative-positive, negative-neutral, and negative-negative cortical support reductions, were simulated. A load of 700 N was applied to simulate a 70 kg elderly patient standing on one leg. The models were subjected to finite element analysis. The displacement and von Mises stress distributions were analyzed.

RESULTS

The positive-positive cortical support reduction pattern showed minimal stress and the negative-negative reduction pattern showed maximal stress on the intramedullary nail. The stress was mainly concentrated at the junction of the helical blade and the main nail and at the site of the lateral aspect of the insertion point of the nail in the great trochanter. The positive cortical support reduction patterns seemed to have smaller maximum displacements of the entire fragment-implant assembly and relative displacements between the head-neck and shaft fragments. Meanwhile, the negative reduction patterns seemed to have larger displacements.

CONCLUSION

The positive-positive support reduction pattern showed better mechanical stability for unstable pertrochanteric fractures. The negative-negative support reduction pattern was prone to fixation failure and should be avoided during an operation.

Biomechanical comparison of medial sustainable nail and proximal femoral nail antirotation in the treatment of an unstable intertrochanteric fracture

AIMS

Restoration of proximal medial femoral support is the keystone in the treatment of intertrochanteric fractures. None of the available implants are effective in constructing the medial femoral support. Medial sustainable nail (MSN-II) is a novel cephalomedullary nail designed for this. In this study, biomechanical difference between MSN-II and proximal femoral nail anti-rotation (PFNA-II) was compared to determine whether or not MSN-II can effectively reconstruct the medial femoral support.

METHODS

A total of 36 synthetic femur models with simulated intertrochanteric fractures without medial support (AO/OTA 31-A2.3) were assigned to two groups with 18 specimens each for stabilization with MSN-II or PFNA-II. Each group was further divided into three subgroups of six specimens according to different experimental conditions respectively as follows: axial loading test; static torsional test; and cyclic loading test.

RESULTS

The mean axial stiffness, vertical displacement, and maximum failure load of MSN-II were 258.47 N/mm (SD 42.27), 2.99 mm (SD 0.56), and 4,886 N (SD 525.31), respectively, while those of PFNA-II were 170.28 N/mm (SD 64.63), 4.86 mm (SD 1.66), and 3,870.87 N (SD 552.21), respectively. The mean torsional stiffness and failure torque of MSN-II were 1.72 N m/° (SD 0.61) and 16.54 N m (SD 7.06), respectively, while those of PFNA-II were 0.61 N m/° (SD 0.39) and 6.6 N m (SD 6.65), respectively. The displacement of MSN-II in each cycle point was less than that of PFNA-II in cyclic loading test. Significantly higher stiffness and less displacement were detected in the MSN-II group (p < 0.05).

CONCLUSION

The biomechanical performance of MSN-II was better than that of PFNA-II, suggesting that MSN-II may provide more effective mechanical support in the treatment of unstable intertrochanteric fractures. Cite this article: Bone Joint Res 2020;9(12):840-847.

Medial support nail and proximal femoral nail antirotation in the treatment of reverse obliquity inter-trochanteric fractures (Arbeitsgemeinschaft fur Osteosynthesfrogen/Orthopedic Trauma Association 31-A3.1): a finite-element analysis

BACKGROUND

The reverse obliquity inter-trochanteric fracture is a distinct fracture pattern that is mechanically different from most inter-trochanteric fractures and the optional treatment of it is still controversial. The purpose of this study was to compare differences in the efficacy of a novel nail (medial support nail [MSN-II]) and proximal femoral nail anti-rotation (PFNA-II) in the treatment of reverse obliquity inter-trochanteric fractures (Arbeitsgemeinschaft fur Osteosynthesfrogen/Orthopedic Trauma Association [AO/OTA] 31-A3.1) using finite-element analysis.

METHODS

Modeling software was used to establish a three-dimensional model of MSN-II and PFNA-II and an A3.1 inter-trochanteric fracture model. Abaqus software was used to implement different force loads to compare finite-element biomechanical parameters such as the maximum stress in implant and the displacement of fracture site.

RESULTS

The femoral stress, implant stress and fracture site displacement of MSN-II was less than that of PFNA-II. The results indicated that the maximal femoral stress was 581 MPa for PFNA-II and 443 MPa for the MSN-II. The maximum stress values in the PFNA-II and MSN-II models were 291 and 241 MPa, respectively. The maximal displacements of the fracture site were 1.47 and 1.16 mm in the PFNA-II and MSN-II models, respectively.

CONCLUSION

Compared with PFNA-II for inter-trochanteric fracture (AO/OTA 31-A3.1), MSN-II which was designed with a triangular stability structure can provide better biomechanical stability. The MSN-II may be a feasible option for the treatment of reverse obliquity inter-trochanteric fracture.