Biomechanical study of two alternative methods for the treatment of vertical femoral neck fractures - A finite element analysis

Finite Element Analysis of Six Internal Fixations in the Treatment of Pauwels Type III Femoral Neck Fracture

OBJECTIVE

The current investigation sought to utilize finite element analysis to replicate the biomechanical effects of different fixation methods, with the objective of establishing a theoretical framework for the optimal choice of modalities in managing Pauwels type III femoral neck fractures.

METHODS

The Pauwels type III fracture configuration, characterized by angles of 70°, was simulated in conjunction with six distinct internal fixation methods, including cannulated compression screw (CCS), dynamic hip screw (DHS), DHS with de-rotational screw (DS), CCS with medial buttress plate (MBP), proximal femoral nail anti-rotation (PFNA), and femoral neck system (FNS). These models were developed and refined using Geomagic and SolidWorks software. Subsequently, finite element analysis was conducted utilizing Ansys software, incorporating axial loading, torsional loading, yield loading and cyclic loading.

RESULTS

Under axial loading conditions, the peak stress values for internal fixation and the femur were found to be highest for CCS (454.4; 215.4 MPa) and CCS + MBP (797.2; 284.2 MPa), respectively. The corresponding maximum and minimum displacements for internal fixation were recorded as 6.65 mm for CCS and 6.44 mm for CCS + MBP. When subjected to torsional loading, the peak stress values for internal fixation were highest for CCS + MBP (153.6 MPa) and DHS + DS (72.8 MPa), while for the femur, the maximum and minimum peak stress values were observed for CCS + MBP (119.3 MPa) and FNS (17.6 MPa), respectively. Furthermore, the maximum and minimum displacements for internal fixation were measured as 0.249 mm for CCS + MBP and 0.205 mm for PFNA. Additionally, all six internal fixation models showed excellent performance in terms of yield load and fatigue life.

CONCLUSION

CCS + MBP had the best initial mechanical stability in treatment for Pauwels type III fracture. However, the MBP was found to be more susceptible to shear stress, potentially increasing the risk of plate breakage. Furthermore, the DHS + DS exhibited superior biomechanical stability compared to CCS, DHS, and PFNA, thereby offering a more conducive environment for fracture healing. Additionally, it appeared that FNS represented a promising treatment strategy, warranting further validation in future studies.

Comparative study of a novel proximal femoral bionic nail and three conventional cephalomedullary nails for reverse obliquity intertrochanteric fractures: a finite element analysis

Purpose

Conventional cephalomedullary nails (CMNs) are commonly employed for internal fixation in the treatment of reverse obliquity intertrochanteric (ROI) fractures. However, the limited effectiveness of conventional CMNs in addressing ROI fractures results in significant implant-related complications. To address challenges associated with internal fixation, a novel Proximal Femoral Bionic Nail (PFBN) has been developed.

Methods

In this study, a finite element model was constructed using a normal femoral specimen, and biomechanical verification was conducted using the GOM non-contact optical strain measurement system. Four intramedullary fixation approaches-PFBN, Proximal Femoral Nail Antirotation InterTan nail (ITN), and Gamma nail (Gamma nail)-were employed to address three variations of ROI fractures (AO/OTA 31-A3). The biomechanical stability of the implant models was evaluated through the calculation of the von Mises stress contact pressure and displacement.

Results

Compared to conventional CMNs, the PFBN group demonstrated a 9.36%-59.32% reduction in the maximum VMS at the implant. The A3.3 ROI fracture (75% bone density) was the most unstable type of fracture. In comparison to conventional CMNs, PFBN demonstrated more stable data, including VMS values (implant: 506.33 MPa, proximal fracture fragment: 34.41 MPa), contact pressure (13.28 MPa), and displacement (17.59 mm).

Conclusion

Compared to the PFNA, ITN, and GN, the PFBN exhibits improvements in stress concentration, stress conduction, and overall model stability in ROI fractures. The double triangle structure aligns better with the tissue structure and biomechanical properties of the proximal femur. Consequently, the PFBN has significant potential as a new fixation strategy for the clinical treatment of ROI fractures.

A finite element analysis of a low-profile femoral neck system of screws in sleeves in a vertical femoral neck fracture model

BACKGROUND

Femoral neck system (FNS) has exhibited some drawbacks, such as non-fit of the plate with the lateral femoral cortex, postoperative pain, and the potential risk of subtrochanteric fractures. We have developed a low-profile FNS system that addresses some compatibility issues in FNS. In this study, we conducted finite element analysis on the 1-hole FNS (1 H-FNS), 2-holes FNS (2 H-FNS), and low-profile FNS (LP-FNS) and compared their biomechanical performance.

METHODS

After the mesh convergence analysis, we established three groups of 1 H-FNS, 2 H-FNS, and LP-FNS. The interfragmentary gap, sliding distance, shear stress, and compressive stress and the bone-implant interface compression stress, stiffness, and displacement were determined under the neutral, flexion, or extension conditions of the hip joint, respectively. The stress and displacement of the femur after the implant removal were also investigated.

RESULTS

(1) There were no obvious differences among the three FNS groups in terms of the IFM distance. However, the LP-FNS group showed less rotational angle compared with conventional FNS (neutral: 1 H-FNS, -61.64%; 2 H-FNS, -45.40%). Also, the maximum bone-implant interface compression stress was obviously decreased under the neutral, flexion, or extension conditions of the hip joint (1 H-FNS: -6.47%, -20.59%, or -4.49%; 2 H-FNS: -3.11%, 16.70%, or -7.03%; respectively). (2) After the implant removal, there was no notable difference in the maximum displacement between the three groups, but the maximum von Mises stress displayed a notable difference between LP-FNS and 1 H-FNS groups (-15.27%) except for the difference between LP-FNS and 2 H-FNS groups (-4.57%).

CONCLUSIONS

The LP-FNS may not only provide the same biomechanical stabilities as the 1 H-FNS and 2 H-FNS, but also have more advantages in rotational resistance especially under the neutral condition of the hip joint, in the bone-implant interface compression stress, and after the implant removal. In addition, the 1 H-FNS and 2 H-FNS have similar biomechanical stabilities except for the maximum von Mises stress after the implant removal. The femur after the LP-FNS removal not only is subjected to relatively little stress but also minimizes stress concentration areas.

Comparison of femoral neck shortening after femoral neck system and cannulated cancellous screw fixation for displaced femoral neck fractures in young adults

BACKGROUND

The purpose of this study was to compare the outcomes of femoral neck shortening between the femoral neck system (FNS) and the cannulated cancellous screws (CCS) for displaced femoral neck fractures in young adults PATIENTS AND METHODS: In this retrospective analysis, 225 patients aged 18-65 years with displaced femoral neck fracture were divided into two groups according to internal fixation: 135 patients in the FNS group and 90 patients in the CCS group. The length of hospital stay, duration of surgery, intraoperative blood loss, quality of reduction, extent of femoral neck shortening, incidence of femoral neck shortening, femoral neck shortening at each follow-up visit, Harris hip score (HHS), reoperation, and complications were compared between the two groups.

RESULTS

The median follow-up time was 28.2 (26.0, 31.2) months in the FNS group and 30.2 (26.3, 34.7) months in the CCS group. The follow-up time, age, sex distribution, body mass index (BMI), mechanism of injury, injured side, length of hospital stay, time from injury to surgery, and fracture classification were similar between the groups. Duration of surgery was longer in the FNS group (65.0 (55.0, 87.0) min versus 55.0 (50.0, 65.0) min, P<0.001); intraoperative blood loss was greater in the FNS group (50.0 (20.0, 60.0) ml versus 20.0 (10.0, 35.0) ml, P<0.001). Femoral neck shortening was 2.4 (1.0, 4.5) mm in the FNS group versus 0.6 (0.0, 2.6) mm in the CCS group at 1 month postoperatively (P<0.001); 3.7 (1.8, 6.4) mm in the FNS group versus 1.2 (0.6, 3.8) mm in the CCS group at 3 months (P<0.001); 4.1(2.4, 7.7) mm in the FNS group versus 2.3 (1.1, 4.4) mm in the CCS group at 6 months (P<0.001); 4.2 (2.6, 7.7) mm in the FNS group versus 2.6 (1.3, 4.6) mm in the CCS group at 12 months (P<0.001); and 4.5 (2.8, 8.0) mm in the FNS group versus 2.8 (1.5, 4.8) mm in the CCS group at 18 months (P<0.001). The two groups showed no significant differences in HHS, reoperation, and reduction quality.

CONCLUSION

Compared to CCS, FNS is deficient in preventing femoral neck shortening. Future research should focus on improving FNS in terms of preventing femoral neck shortening.

Biomechanical Stability of Femoral Neck System for Pauwels Type III Femoral Neck Fractures Based on Different Reduction Quality

To further investigate the biomechanics of a femoral neck system (FNS) for Pauwels type III femoral fractures based on three different reductions.We constructed three different reduction (anatomical reduction, negative buttress reduction, and positive buttress reduction) models of Pauwels type III femoral neck fractures. Then, three cannulated screws (3CS), dynamic hip screws (DHS), dynamic hip screws combined with an anti-rotation screw (DHS + ARS), one-hole femoral neck system (1HFNS), and two-hole femoral neck system (2HFNS) were assembled with the reduction models, respectively, to simulate the internal fixation surgical procedure. All models had a load of 2100 N in line with the femoral mechanical axis applied. The implant stress, the head and implant displacements, and the rotational angles of all models were recorded and analyzed.Compared to 3CS and 2HFNS, 1HFNS had higher implant stress (higher than 92.5 MPa and 46.3 MPa, respectively) and displacement (higher than 0.9 mm and 0.8 mm, respectively) in the anatomical reduction. 2HFNS exhibited the highest stress values (225.5 MPa) in the anatomical reduction but the lowest values (159.8 MPa) in the positive buttress reduction when compared to the other implants. 2HFNS showed the best rotational stability in the negative and positive buttress reduction (rotational angels of 0.8° and 0.6°, respectively).Based on the outcome of this computational study, it might be concluded that 2HFNS was an alternative fixation for the treatment of Pauwels type III femoral neck fracture, especially when anatomical reduction cannot be perfectly attained. More relevant clinical and biomechanical studies are needed in the future.

Single-plane osteotomy model is inaccurate for evaluating the optimal strategy in treating vertical femoral neck fractures: A finite element analysis

BACKGROUND AND OBJECTIVES

The conventional method for simulating vertical femoral neck fractures (vFNFs) is via a vertical single-plane osteotomy (SPO) across the entire femur. However, the accuracy of SPO for evaluating the optimal internal fixation strategy (IFS) and the appropriate assessment parameters is not clear. This study thus aimed to examine the accuracy of SPO in evaluating IFSs and to identify appropriate evaluation parameters using finite element analysis.

METHODS

Eighty patient-specific finite element models were developed based on CT images from eight vFNF patients. The natural fracture model was built using structural features of the affected side, while the SPO was simulated on the healthy side. Five different IFSs were applied to both the natural fracture and SPO groups. Thirteen parameters, including stress, displacement, and stiffness, were subjected to a two-way repeated measures ANOVA to determine the effect of IFSs and fracture morphology on stability. A Pearson correlation analysis was performed on varied parameters with various IFSs to identify independent parameters. Based on these independent parameters, the entropy evaluation method (EEM) score was used to rank the performance of IFSs for each patient.

RESULTS

Eight of the thirteen parameters were significantly influenced by IFSs (p < 0.05), two by fracture morphology (p < 0.01), and none by the interaction between IFS and fracture morphology. In the natural fracture group, parameters including screw stress and displacement, bone cut rate (BCR), and compression effects varied independently with distinct IFSs. In the SPO group, trunk displacement, BCR, cut-out risk, and compression effects parameters changed independently. The BCR of the Alpha strategy was significantly higher than that of the Inverted strategy in the natural fracture group (p = 0.002), whereas the opposite was observed in the SPO group (p = 0.016). Regarding compression effects, two IFS pairings in the natural fracture group and seven IFS pairings in the SPO group exhibited significant differences. None of the five IFSs achieved the optimal EEM score for each patient.

CONCLUSIONS

The single-plane osteotomy model may have limitations in assessing IFSs, particularly when the bone cut rate and compression effects are the main influencing factors. Parameters of the screw stress and displacement, BCR, and compression effects appear to be relevant in evaluating IFSs for natural fracture models. It indicates that individualized natural fracture models could provide more comprehensive insights for determining the optimal IFS in treating vFNFs.

The novel magnesium-titanium hybrid cannulated screws for the treatment of vertical femoral neck fractures: Biomechanical evaluation

Background

Conventional cannulated screws are commonly used for internal fixation in the treatment of vertical femoral neck fractures. However, the noticeably high rates of undesirable outcomes such as nonunion, malunion, avascular necrosis, and fixation failure still troubled the patients and surgeons. It is urgent to develop new cannulated screws to improve the above clinical problems. The purpose of this study was to design a novel magnesium-titanium hybrid cannulated screw and to further evaluate its biomechanical performance for the treatment of vertical femoral neck fractures.

Methods

A novel magnesium-titanium hybrid cannulated screw was designed, and the conventional titanium cannulated screw was also modeled. The finite element models for vertical femoral neck fractures with magnesium-titanium hybrid cannulated screws and conventional cannulated screws were respectively established. The hip joint contact force during walking gait calculated by a subject-specific musculoskeletal multibody dynamics model, was used as loads and boundary conditions for both finite element models. The stress and displacement distributions of the cannulated screws and the femur, the micromotion of the fracture surfaces of the femoral neck, and the overall stiffness were calculated and analyzed using finite element models. The biomechanical performance of the Magnesium-Titanium hybrid cannulated screws was evaluated.

Results

The maximum stresses of the magnesium-titanium hybrid cannulated screws and the conventional cannulated screws were 451.5 ​MPa and 476.8 ​MPa, respectively. The maximum stresses of the femur with the above different cannulated screws were 140.3 ​MPa and 164.8 ​MPa, respectively. The maximum displacement of the femur with the hybrid cannulated screws was 6.260 ​mm, lower than the femur with the conventional cannulated screws, which was 7.125 ​mm. The tangential micromotions in the two orthogonal directions at the fracture surface of the femoral neck with the magnesium-titanium hybrid cannulated screws were comparable to those with the conventional cannulated screws. The overall stiffness of the magnesium-titanium hybrid cannulated screw system was 490.17 ​N/mm, higher than that of the conventional cannulated screw system, which was 433.92 ​N/mm.

Conclusion

The magnesium-titanium hybrid cannulated screw had superior mechanical strength and fixation stability for the treatment of the vertical femoral neck fractures, compared with those of the conventional cannulated screw, indicating that the magnesium-titanium hybrid cannulated screw has great potential as a new fixation strategy in future clinical applications.The translational potential of this article: This study highlights an innovative design of the magnesium-titanium hybrid cannulated screw for the treatment of vertical femoral neck fractures. The novel magnesium-titanium hybrid cannulated screw not only to provide sufficient mechanical strength and fixation stability but also to contribute to the promotion of fracture healing, which could provide a better treatment for the vertical femoral neck fractures, beneficially reducing the incidence of nonunion and reoperation rates.

Femoral neck system and cannulated compression screws in the treatment of non-anatomical reduction Pauwels type-III femoral neck fractures: A finite element analysis

BACKGROUND

High shear force is a major factor detrimental to the healing of vertical femoral neck fractures. In addition to firm fixation, reduction quality is crucial for postoperative stability. The present study aimed to compare the biomechanical stability of the newly invented femoral neck system and three inverted-triangle cannulated compression screws treatments for non-anatomical reduction of Pauwels type-III femoral neck fractures.

METHODS

A total of 18 non-anatomical reduction Pauwels type-III femoral neck fracture finite element models were fabricated and fixed using three inverted-triangle cannulated compression screws or the femoral neck system. A 1950-N force was applied to the femoral head to simulate the physiological load during a single-leg stance. Parameters of the maximum total deformation, the interfragmentary gap, and the maximum von Mises stress of the implants and the proximal femur were analyzed.

FINDINGS

The results of the maximum total deformation, interfragmentary gap, and maximum von Mises stress of the implants in the negative-negative buttress model fixed by the femoral neck system were the largest among all groups (3.58 mm, 0.252 mm, and 729.68 MPa, respectively). In contrast, the anatomical-anatomical reduction model fixed by three inverted-triangle cannulated compression screws demonstrated the minimum total deformation, interfragmentary gap, and minimum von Mises stress of implants (1.107 mm, 0.09 mm, and 189.83 MPa, respectively).

INTERPRETATION

Anatomical reduction or positive buttress in femoral neck fractures should be recommended during fracture reduction. The femoral neck system showed weaker biomechanical stability than three inverted-triangle cannulated compression screws in treating Pauwels type-III femoral neck fractures.

Biomechanical analysis of different internal fixation methods for special Maisonneuve fracture of the ankle joint based on finite element analysis

OBJECTIVE

The objective of this study was to evaluate the biomechanical properties of different internal fixation methods for Maisonneuve fractures under physiological loading conditions.

METHODS

Finite element analysis was used to numerically analyze various fixation methods. The study focused on high fibular fractures and included six groups of internal fixation: high fibular fracture without fixation + distal tibiofibular elastic fixation (group A), high fibular fracture without fixation + distal tibiofibular strong fixation (group B), high fibular fracture with 7-hole plate internal fixation + distal tibiofibular elastic fixation (group C), high fibular fracture with 7-hole plate internal fixation + distal tibiofibular strong fixation (group D), high fibular fracture with 5-hole plate internal fixation + distal tibiofibular elastic fixation (group E), and high fibular fracture with 5-hole plate internal fixation + distal tibiofibular strong fixation (group F). The finite element method was employed to simulate and analyze the different internal fixation models for the six groups, generating overall structural displacement and Von Mises stress distribution maps during slow walking and external rotation motions.

RESULTS

Group A demonstrated the best ankle stability under slow walking and external rotation, with reduced tibial and fibular stress after fibular fracture fixation. Group D had the least displacement and most stability, while group A had the largest displacement and least stability. Overall, high fibular fracture fixation improved ankle stability. In slow walking, groups D and A had the least and greatest interosseous membrane stress. Comparing 5-hole plate (E/F) and 7-hole plate (C/D) fixation, no significant differences were found in ankle strength or displacement under slow walking or external rotation.

CONCLUSION

Combining internal fixation for high fibular fractures with elastic fixation of the lower tibia and fibula is optimal for orthopedic treatment. It yields superior outcomes compared to no fibular fracture fixation or strong fixation of the lower tibia and fibula, especially during slow walking and external rotation. To minimize nerve damage, a smaller plate is recommended. This study strongly advocates for the clinical use of 5-hole plate internal fixation for high fibular fractures with elastic fixation of the lower tibia and fibula (group E).

What makes vertical femoral neck fracture with posterior inferior comminution different? An analysis of biomechanical features and optimal internal fixation strategy

BACKGROUND AND PURPOSE

Fracture comminution occurs in 83.9%-94% of vertical femoral neck fractures (VFNFs), the majority of which were located in posterior-inferior region, and poses a clinical challenge in fixation stability. We conducted a subject-specific finite element analysis to determine the biomechanical features and optimal fixation selection for treating VFNF with posterior-inferior comminution.

PATIENTS AND METHODS

Eighteen models with three fracture types (VFNF without comminution [NCOM], with comminution [COM], with comminution + osteoporosis [COMOP]) and six internal fixation types (alpha [G-ALP], buttress [G-BUT], rhomboid [G-RHO], dynamic hip screw [G-DHS], invert triangle [G-ITR], femoral neck system (G-FNS)) were created based on the computed tomography data. By using the subject-specific finite element analysis method, stiffness, implant stress, yielding rate (YR) were compared. Additionally, in order to elucidate distinct biomechanical characters of different fracture types and fixation strategies, we calculated interfragmentary movement (IFM), detached interfragmentary movement (DIM), shear interfragmentary movement (SIM) of all fracture surface nodes.

RESULTS

Generally, in comparison with NCOM, COM showed a 30.6% reduction of stiffness and 1.46-times higher mean interfragmentary movement. Besides, COM had a 4.66-times (p = 0.002) higher DIM at the superior-middle position, but similar SIM across fracture line, which presented as varus deformation. In COM and COMOP, among all six fixation strategies, G-ALP had significantly the lowest IFM (p<0.001) and SIM (p<0.001). Although G-FNS had significantly highest IFM and SIM (p<0.001), it had the highest stiffness and lowest DIM (p<0.001). In COMOP, YR was the lowest in G-FNS (2.67%).

CONCLUSIONS

Posterior-inferior comminution primarily increases superior-middle detached interfragmentary movement in VFNF, which results in varus deformation. For comminuted VFNF with or without osteoporosis, alpha fixation has the best interfragmentary stability and anti-shear property among six current mainstream fixation strategies, but a relatively weaker stiffness and anti-varus property compared to fixed-angle devices. FNS is advantageous owing to stiffness, anti-varus property and bone yielding rate in osteoporosis cases, but is insufficient in anti-shear property.

Biomechanical comparison of femoral neck system and cannulated screws coupled with medial plate for treating Pauwels III femoral neck fractures

BACKGROUND

The femoral neck system (FNS) has been considered as a novel strategy for femoral neck fracture. The diversity of internal fixation creates difficulties in choosing an effective option for Pauwels III type femoral neck fractures. Therefore, it is significant to investigate the biomechanical effects of FNS versus conventional approaches on bones.

OBJECTIVE

To evaluate the biomechanical characteristics of FNS versus cannulated screws coupled with medial plate (CSS+MP) for the treatment of Pauwels III type femoral neck fractures.

METHODS

Through three-dimensional computer software (Minics, Geomagic - Warp), the proximal femur model was rebuilt. Based on the present clinical characteristics, models of internal fixation were reconstructed in SolidWorks, including cannulated screws (CSS), medial plate (MP) and FNS. After parameter setting and meshing, boundary conditions and loads were set up for the final mechanical calculation in Ansys Software. Under identical experimental conditions, such as the same Pauwels angle and force loading, the peak values of displacement, shear stress and equivalent (von Mises) stress were recorded.

RESULTS

This study showed that the displacement of the models was CSS, CSS+MP, and FNS in descending order of magnitude. The shear stress and equivalent stress of the models was CSS+MP, FNS, and CSS in descending order. The principal shear stress of CSS+MP was concentrated on the medial plate. The equivalent stress of FNS was more dispersed and distributed from the proximal main nail to the distal locking screw.

CONCLUSION

CSS+MP and FNS exhibited better initial stability compared to CSS. However, the MP was subjected to more shear stress, which could increase the risk of internal fixation failure. Due to its unique design, FNS may be a good choice for the treatment of Pauwels III type femoral neck fractures.

Survivability of the Femoral Neck System for the treatment of femoral neck fractures in adults

INTRODUCTION

Hip fractures are common injuries in the elderly, with an incidence that continues to rise. The femoral neck system (FNS) recently emerged as a novel treatment option for femoral neck fractures, but long-term survivability of the implant remains uncertain. The purpose of this study is to evaluate survivability of the FNS and assess risk factors for implant failure.

METHODS

One hundred five adult patients who received the FNS (DePuy Synthes, Raynham, MA) for femoral neck fractures (AO/OTA 31B) were included. Surgeries were performed within a regional hospital system comprising 18 facilities. All patients had a minimum follow-up of 1 year. The primary outcome measures were cumulative incidence of implant failure and 1-year mortality, including risk factor analysis.

RESULTS

Twelve implants failed at a follow-up ranging from 17 days to 8 months, and 7 failed within 90 days. Cumulative incidence of implant failure was 2% at 30 days, 7% at 90 days, 12% at 6 months, and 13% at 1 year. Causes of implant failure included cut-out (n = 5), non-union (n = 4), peri-implant fracture (n = 2), and avascular necrosis (n = 1). Univariate Cox regression identified Pauwels type III fractures and an increasing AP Parker ratio as significant risk factors for failure. Pauwels type III fractures showed a 5.48 times higher risk compared to Pauwels types I & II. Every 10% increase in AP Parker ratio increased risk of failure by 2.39 times. The 1-year mortality rate was 21%, and univariate logistic regression identified age as the only risk factor (odds ratio = 3.71).

CONCLUSIONS

The incidence of implant failure and 1-year mortality rate in this study suggests that the FNS can provide reliable fixation compared to rates in the literature, but complications are not uncommon. Avoiding Pauwels type III fractures and optimizing implant placement appear crucial to preventing implant failure.

LEVEL OF EVIDENCE

Therapeutic Level IV.

Finite element comparative analysis of three different internal fixation methods in the treatment of Pauwels type III femoral neck fractures

BACKGROUND

Comparison of 4 cannulated lag screws (3 inverted triangular cannulated screws + anti-rotating screws;4 CLS), dynamic hip screws + derotational screws (DHS + DS), and femoral neck fixation system (FNS) in the treatment of Biomechanical properties of middle-aged Pauwels type III femoral neck fractures.

METHODS

The femur CT data of a healthy young volunteer was selected and imported into Mimics software to construct a three-dimensional model of a normal femur. Pauwels type III femoral neck fractures were simulated according to the 70° fracture line. Use Geomagic and SolidWorks software to optimize and build CLS, DHS + DS, and FNS fracture internal fixation models. Finally, Ansys software was used to analyze the stress distribution, peak value, and maximum displacement of the proximal fracture fragment and internal fixation; the displacement distribution, and peak value of the fracture surface at the fracture end.

RESULTS

① The stress peaks of the proximal fracture fragments in the three groups were concentrated near the femoral calcar. The peak stress of the FNS group was the largest, and the DHS + DS group was the smallest. ②The displacement of the fracture fragments was all located at the top of the femur. The peak displacement of the FNS group was the largest, and the DHS + DS group was the smallest. ③ The internal fixation stress of the three groups is concentrated in the middle part of the device. The stress distribution of the first two groups of models is more uniform than that of FNS. The peak stress of FNS is the largest and the CLS is the smallest. ④ The internal fixed displacements are all located at the top of the model. The peak displacement of the CLS is the largest, and the DHS + DS is the smallest. ⑤ The displacement of the fracture surface is in the upper part of the fractured end. The peak displacement of the FNS group was the largest, and the DHS + DS group was the smallest.

CONCLUSION

Compared with the other two internal fixation methods, dynamic hip screw + derotational screw (DHS + DS) showed good biomechanical stability. When Pauwels type III femoral neck fracture occurs in young adults, DHS + DS can be given priority as the preferred treatment for this type of fracture.

Biomechanical evaluation of different internal fixation methods based on finite element analysis for Pauwels type III femoral neck fracture

BACKGROUND AND OBJECTIVE

The best internal fixation method for the treatment of Pauwels type III femoral neck fractures (FNFs) remains to be demonstrated. Through finite element analysis, this study explored whether dynamic hip screw (DHS) combined with anti rotation screw or medial buttress plate can improve the stability of internal fixation, and the femoral neck system (FNS) with similar structure to DHS and the traditional cannulated screw (CSs) were added for comparison. To evaluate their respective biomechanical advantages and disadvantages in the treatment of Pauwels type III FNFs.

METHODS

Six groups of internal fixation models for the treatment of FNFs were established, including CSs, DHS, DHS combined with single anti-rotation screw (DHS + SS), and DHS combined with both anti-rotation screw (DHS + BS), DHS combined with medial buttress plate (DHS + MBP), new femoral neck internal fixation system (Femoral Neck System, FNS). Four finite element analysis models were established for each group, evaluation of femoral displacement and internal fixation stress during stair climbing and walking conditions, and the contact force of the hip joint was used in two cases, dynamic and static.

RESULTS

The fracture plane motion and peak stress of internal fixators were the lowest with DHS + BS and CSs fixation, and the two results are very close, The peak value of DHS combined with anti rotation screw or medial buttress plate is much lower than that of DHS, indicating that the fixation effect of the combined model is enhanced, and there is no significant difference between FNS and DHS + SS.

CONCLUSION

Both the anti rotation screw and medial buttress plate can effectively reduce the movement of fracture section and share the shear force of DHS, FNS has the similar fixation stability to DHS + SS, DHS + BS has the biomechanical advantages of significantly reducing the risk of internal fixation failure and femoral yield. Therefore, the use of DHS + BS may be a more favorable choice in the case of Pauwels type III FNFs with higher fixation requirements.

Plate configuration for biological reconstructions of femoral intercalary defect - a finite element evaluation

BACKGROUND AND OBJECTIVE

Biological reconstruction was commonly used for femoral intercalary defect. The initial stability by plate fixation was believed to have an effect on bone union and implant failure. Our study was proposed to explore relationship of plate configuration and initial stability for femoral intercalary reconstruction using allo-/autograft.

METHODS

Femoral intercalary defect models were established with four different plate configurations: (1) Single lateral bridging plate, SLP (2) Lateral bridging plate + Orthogonal adjuvant plate, LP+OAP (3) Lateral bridging plate + Medial adjuvant plate, LP+MAP (4) Lateral bridging plate + Medial bridging plate, LP+MP. A diaphysis defect of 12 cm was simulated, and the removed native femoral bone was used as a structural allograft with the osteotomy gap of 2 mm. Models were analyzed by finite element simulations under an axial compression of 2000N and an axial moment of 10 Nm, respectively.

RESULTS

Axial load: (1) The peak von Mises stress of SLP, LP+OAP, LP+MAP, LP+MP were 993.50 MPa, 335.63 MPa, 240.03 MPa, 281.73 MPa, respectively and LP+MAP was the lowest (p < 0.01); (2) The mean displacement of SLP, LP+OAP, LP+MAP, LP+MP was 0.765, 0.130, 0.121, 0.235 mm, respectively. LP+MAP showed the best stability while SLP had a crash in the medial proximal gap; (3) The LP+MAP configuration had the most uniform stress distribution and the lowest maximum von Mises stress of 79.7 MPa within plates. Axial torsional load: (1) The peak von Mises stress of SLP, LP+OAP, LP+MAP, LP+MP were 431.66Mpa, 120.73 MPa, 72.31 MPa, 109.86 MPa, respectively; (2) The rotation angle of SLP, LP+OAP, LP+MAP, LP+MP was 4.30°, 1.35°, 1.20°, 1.57°, respectively. All of LP+OAP, LP+MAP and LP+MP showed an optimal torsional stability.

CONCLUSIONS

For femoral intercalary reconstruction using allo-/autograft fixed by plates, LP+MAP and LP+MP configurations showed superior stability in terms of axial compression and torsion load by FE simulation. A better stability was believed to be associated with higher union rate and lower hardware failure rate.