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

A New Postoperative Stability Score to Predict Loss of Reduction in Intertrochanteric Fractures in Elderly Patients

The study aimed to validate a newly developed postoperative stability score for evaluating clinical follow-up in elderly patients with low-energy hip fractures. From 1 January 2020 to 31 December 2021, we enrolled patients aged over 65 who underwent cephalomedullary nail fixation using proximal femoral nail antirotation II (PFNAII) and had at least 6 months of follow-up; excluding multiple fractures, pathological fractures, and periprosthetic fractures. We collected general patient data. Parameters such as TAD, Parker's ratio (AP and lateral), and the new postoperative stability score were recorded. A loss of reduction was defined using the decline in the Chang reduction quality criteria (CRQC) score within one month. Among the 108 enrolled patients, 23 (21.3%) experienced a loss of reduction, with a mean age of 82.1 years and a mean follow-up time of 7.4 months. Univariate analysis showed no significant association between loss of reduction and general data. However, the new postoperative stability score correlated significantly with loss of reduction (mean scores: 6.68 vs. 4.83, p = 0.045). Multivariate analysis confirmed this association (odds ratio: 0.076, 95% confidence interval: 0.022-0.263, p < 0.05). The newly developed postoperative stability score, incorporating surgical technique assessment, improves prediction accuracy for loss of reduction in elderly intertrochanteric fracture (ITF) 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.

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.

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.

Finite element analysis of the effect of residual lateral wall volume on postoperative stability in intertrochanteric fractures

BACKGROUND

Lateral wall fractures represent crucial risk factors for postoperative internal fixation failure in intertrochanteric femoral fractures. However, no consensus exists on the type of lateral wall fracture requiring interventional management. This study aimed to investigate the effect of residual lateral wall volume on the postoperative stability of intertrochanteric femur fractures with associated lateral wall fractures, providing valuable reference for the clinical management of the lateral wall.

METHODS

Eleven bone defect models of intertrochanteric femur fractures with varying residual lateral wall volumes were constructed using finite element analysis. These models were fixed with proximal femoral nail antirotation (PFNA). Simulations of von Mises stress and displacement distribution of the PFNA and femur during normal walking were conducted. Statistical analysis was performed to assess the correlation between volume and the maximum von Mises stresses and displacements of the PFNA and femur.

RESULTS

In all 11 models, the maximum von Mises stress and displacement of the helical blade, intramedullary nail, and femur occurred at the same locations. As residual lateral wall volume increased, the maximum von Mises stress and displacement of the helical blade, intramedullary nail, and maximum femoral displacement gradually decreased. However, the overall trend of the maximum femoral von Mises stress gradually decreased. At 70% retention of the residual lateral wall volume, there was a more pronounced change in the value of the maximum stress change of the helical blade and the intramedullary nail. Statistical analysis, including the Shapiro-Wilk test and Pearson correlation analysis, demonstrated a significant negative correlation between volume and the maximum von Mises stress and displacement of the helical blade, intramedullary nail, and femur. Linear regression analysis further confirmed this significant negative correlation.

CONCLUSION

Finite element analysis of the residual lateral wall revealed a significant correlation between volume and the postoperative stability of intertrochanteric femur fractures. A volume of 70% may serve as the threshold for stabilizing the residual lateral wall. Volume emerges as a novel index for evaluating the strength of the residual lateral walls.

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.

Is Sliding Compression Necessary for Intramedullary Nailing Fixation of AO/OTA Type A3.3 Intertrochanteric Fracture?

OBJECTIVES

The intramedullary nail is considered the gold standard for treating AO/OTA type A3.3 intertrochanteric fractures. However, it still faces a significant rate of failure, mainly due to the critical factor of comminuted lateral wall defects leading to inadequate proximal sliding compression. The primary objective of this study is to investigate the requirement of sliding compression in the treatment of unstable AO/OTA type A3.3 intertrochanteric fractures. To achieve this, we conduct a comparative analysis between two approaches: InterTAN alone and proximal femoral anti-rotation blade nailing (PFNA) combined with lateral wall reconstruction for treating AO/OTA type A3.3 intertrochanteric fractures with lateral wall damage.

METHODS

A retrospective analysis was conducted on the clinical data of patients who underwent intramedullary nailing fixation for AO/OTA type A3.3 intertrochanteric fractures at our hospital from January 2012 to January 2022. Patient characteristics as well as treatment details, including operative time, intraoperative blood loss, weight-bearing time, fracture healing time, tip apex distance (TAD) loss, Harris hip scores (HHS), Parker-Palmer mobility score (PPMS), and postoperative complications, were collected and analyzed. Continuous variables were analyzed using independent sample t-tests, while categorical variables were examined using the chi-square test. For group comparisons, variance analysis was applied, and pairwise comparisons were conducted using the LSD-t test.

RESULTS

These patients were divided into PFNA combined with lateral wall reconstruction group (sliding compression group) and InterTAN fixation group (static fixation group) based on surgical methods. The operation time, intraoperative bleeding loss, HHS at 12 months and PPMS at 12 months in the sliding compression group were significantly higher than those in the static fixation group, and time to weight-bearing and fracture healing time were significantly lower than those in the static fixation group (p < 0.05). There were no significant differences between two groups in terms of the TAD at 2 days, 2, and 12 months postoperatively, the incidence of complications (p > 0.05). At 6 months postoperatively, femoral neck length was shortened compared to 2 days postoperatively in both groups, and the sliding compression group had a significantly greater degree of femoral neck shortening than the static fixation group (p < 0.05).

CONCLUSION

The use of PFNA with lateral wall reconstruction for A3.3 intertrochanteric fractures demonstrated superior mobility, efficiency, and reduced internal fixation failure rates compared to InterTAN. These findings suggest that sliding compression may be required for intramedullary nailing treatment.

Clinical observation and finite element analysis of femoral stable interlocking intramedullary nail in intertrochanteric fractures

PURPOSE

This study was designed to compare clinical outcomes of the femoral stable interlocking intramedullary nail (FSIIN) with proximal femoral nail anti-rotation (PFNA) for the treatment of intertrochanteric fractures (OTA 31A1 + A2).

METHODS

This study retrospectively analyzed a registered sample of 74 intertrochanteric fractures (OTA 31A1 + A2) surgically treated using FSIIN (n = 36) or PFNA (n = 38) from January 2015 to December 2021. The intra-operative variables (operation time, fluoroscopy time, intra-operative blood loss, length of incision) and fracture healing time were compared between the two groups in this study. Harris hip score (HHS) and visual analog scale (VAS) were used to evaluate the functional states. At the last follow-up, the incidence of related complications in patients was calculated. Eventually, the 3D finite element model was established to analyze the stress of FSIIN and PFNA.

RESULTS

The distribution of all basic characteristics was similar between the two groups (p > 0.05). The operation time, fluoroscopy time, intra-operative blood loss, and length of incision were significantly decreased in the FSIIN group (p < 0.001). The FSIIN group had a shorter fracture healing time than the PFNA group (p < 0.001). There is no significant difference between the two groups in the Harris and VAS (p > 0.05). The incidences of post-operative anaemia, electrolyte imbalance, varus malalignment, and thigh pain were significantly lower in FSIIN than in PFNA groups (all p < 0.05). The finite element results show that the stress shielding effect of FSIIN is smaller.

CONCLUSIONS

Our study revealed that FSIIN seemed to be superior to PFNA in the treatment of intertrochanteric fractures (OTA 31A1 + A2) due to less surgical damage and shorter fracture healing time.

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.

A comparative Study of Novel Extramedullary Fixation and Dynamic Hip Screw in the Fixation of Intertrochanteric Fracture: A Finite-Element Analysis

Background

Dynamic hip screw (DHS) is one of the most widely internal fixations for stabilizing intertrochanteric fracture, however, with a high risk of postoperative complications. The triangle support fixation plate (TSFP) is developed to reduce the postoperative complications. The purpose of study is to evaluate the biomechanical performance of the DHS and TSFP and demonstrate the rationality of triangular internal fixation for stabilizing intertrochanteric fractures.

Methods

The CT data of the proximal femur were used to establish finite-element models. Evans type I and IV intertrochanteric fracture were constructed and stabilized with the DHS and TSFP. The Von-Mises stress, maximum principal stress, minimum principal stress, and displacement were used to evaluate the biomechanical effect of two implants on intertrochanteric fracture.

Results

Under a 600N axial load, the maximum stress and displacement of an intact proximal femur were 13.78 MPa and 1.33 mm, respectively. The peak stresses of the bone in the TSFP were 35.41 MPa and 68.97 MPa for treating Evans type I and IV intertrochanteric fractures, respectively, which were lower than those in the DHS. The maximum overall displacement and relative distance of the fracture surface in the DHS fixation model were 1.66 mm and 0.10 mm for treating Evans type I intertrochanteric fracture, which was 29.59% and 150% higher than that in the TSFP, and were 2.24 mm and 0.75 mm for treating Evans type IV intertrochanteric fracture, which was 42.58% and 650% higher than that in the TSFP.

Conclusions

In conclusion, the TSFP has obvious advantages in stress distribution and stability than the DHS, providing a promising option for the treatment of intertrochanteric fractures.

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.