Cement augmentation of the proximal femoral nail antirotation for the treatment of osteoporotic pertrochanteric fractures--a biomechanical cadaver study.

INTRODUCTION: Proximal femoral fractures will gain increasing importance in the future due to the epidemiological development. Osteoporosis is often a limiting factor in the achievement of implant stability. New nailing systems offer the possibility of augmentation of the femoral neck component with cement. The aim of this study was to perform a biomechanical comparison of implant stability in osteoporotic pertrochanteric fractures using the proximal femoral nail antirotation (PFNA, Synthes GmbH, Umkirch, Germany) with cement augmented and non-augmented blades.

MATERIALS AND METHODS: Bone mineral density (BMD) was measured by dual-energy X-ray absorptiometry (DEXA) in six pairs of fresh-frozen human femurs. Standardised pertrochanteric fractures (AO31-A2.3) were treated with a PFNA. Cement augmentation was performed in six constructs. Axial loading was applied according to a single-leg-stance model using a hydraulic testing machine increasing to 1400N over 10,000 cycles. Biomechanical comparisons between the two groups that were comparable concerning BMD, tip-apex-distance and native stiffness were made with regard to postoperative stiffness, survived cycles, load to failure, failure mechanism and axial displacement.

RESULTS: The stiffness of all stabilised femurs was significantly lower than for native specimens (native 702.5±159.6N/mm vs. postoperative 275.4±53.8N/mm, p<0.001). Stiffness after instrumentation was significantly greater for the cement augmented group than for the non-augmented group (300.6±46.7N/mm vs. 250.3±51.6N/mm, respectively, p=0.001). Five of the twelve constructs survived cyclic testing. Statistically significant differences of the BMD were detected between survived and failed constructs (0.79±0.17g/cm(2) vs. 0.45±0.12g/cm(2), respectively, p=0.028). The failure loads for specimens surviving 10,000 cycles were 4611.9±2078.9N in the cement augmented group (n=3) and 4516.3N and 3253.5N in the non-augmented group (n=2). Postoperative stiffness was found to be a positive predictor of maximum force to failure (R(2)=0.83, p=0.02).

CONCLUSIONS: The results of this biomechanical study show that cement augmentation of the PFNA increases the implant stability in osteoporotic pertrochanteric fractures. Further studies are necessary to evaluate this procedure in providing long term clinical results.