Abstract
BackgroundThere 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.MethodsFour 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.ResultsCutout 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.ConclusionOur 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.
Highlights
Proximal femoral nail antirotation (PFNA) has a better clinical effect than other internal fixators in treating intertrochanteric fractures, especially the unstable type [1, 2]
After reinforced by bone cement, there was no relative displacement or cutting effect occurred between helical blade and femoral head in both AO31-A1.3 and AO31-A2.2 models
As for femur, before two models were strengthened, the stress of the femur was concentrated on medial part of intertrochanteric region and the stress of AO31-A2.2 was higher than that of AO31-A1.3
Summary
Proximal femoral nail antirotation (PFNA) has a better clinical effect than other internal fixators in treating intertrochanteric fractures, especially the unstable type [1, 2]. The application of bone cement (Polymethylmethacrylate, PMMA) could potentially reduce the risk of cutout complications and reoperations. It is reported that there was a low risk of negative biological side effects of cement augmentation (i.e. pressureinduced avascular necrosis) [7, 8]. There are concerns regarding initial stability and cutout effect in proximal femoral nail antirotation (PFNA) treating intertrochanteric fractures. 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
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