gms | German Medical Science

Objectives: Hip fractures constitute the most debilitating complication of osteoporosis with a steadily increasing incidence in an aging population. Intramedullary nailing of osteoporotic and osteopenic proximal femoral fractures can be challenging because of poor implant anchorage in the femoral head. The recently introduced TFN-ADVANCED Proximal Femoral Nailing System (TFNA) gives the surgeon the freedom of choice to select intraoperatively either a helical blade or a screw as a fixation element in the femoral head. As most of the hip fractures occur in osteoporotic and osteopenic bone, bone cement augmentation might be indicated. So far, no biomechanical studies have investigated the effect of cement augmentation on the fixation strength of these two different types of TFNA elements. Therefore, the aim of this study was to assess the impact of bone cement augmentation on the fixation strength and cut-out resistance of TFNA blades and screws within the femoral head in a human cadaveric model.

Methods: Ten pairs of fresh-frozen osteoporotic and osteopenic human cadaveric femoral heads were randomized to 2 paired groups with 5 pairs each for instrumentation with either a TFNA blade or a TFNA screw. The implant in one specimen of each pair was augmented with PMMA-based bone cement, whereas its contralateral part was left without such an augmentation. All specimens were biomechanically tested under progressively increasing cyclic loading until construct failure in a setup simulating an unstable intertrochanteric fracture with lack of posteromedial support and load sharing at the fracture gap. Varus tilting was monitored by an incliniometer mounted on the femoral head. A varus collapse of 5° was defined as clinically relevant failure criterion and the number of cycles to failure was determined together with the corresponding load at failure for each specimen. Statistical evaluation was performed at a level of significance P=0.05.

Results and conclusion: Cycles to failure for augmented/non-augmented TFNA blades and screws were 30492±8715/19131±11160 and 19307±802/12612±9138, respectively. The corresponding loads at failure were 4049.2±871.5N/2913.1±1116.0N and 2930.7±802.1N/2261.2±913.8N. Both cycles to failure and loads at failure were significantly higher for augmented versus non-augmented TFNA blades (P=0.003) and TFNA screws (P=0.032). The increase in cycles to failure between non-augmented and augmented TFNA blades/screws was 59.4%/53.1% on average. The corresponding increase in loads at failure was 40.0%/29.6%. Implant augmentation with PMMA-based bone cement significantly increases the fixation strength and cut-out resistance of TFNA blades and screws within the femoral head. From a biomechanical perspective it is a valid supplementary treatment option in osteoporotic bone.