Retrograde bridging nail in periprosthetic femoral fracture treatment which allows direct weight bearing

The bridging nail is a retrograde intramedullary femoral nail designed to stabilize periprosthetic femoral fractures. It offers a minimal invasive surgical approach in combination with early mobilization. The goal of this study was to evaluate the osteosynthesis under full weight-bearing conditions. Three groups of five composite fibreglass femora were prepared with a cemented hip stem. Group 1 underwent cyclic axial loading with 1500 N during 150 000 cycles. After completion, linear loading to failure was conducted. Groups 2 and 3 were submitted to linear increased torsional loading with and without an axial load respectively. Failure was defined as rotational movement of the connection (slippage). In the axial cyclic loading configuration, one specimen failed after 122 000 cycles. Four specimens passed 150 000 cycles and failed after linearly increasing the axial loading of 1940–2600 N (mean, 2408 N ± 313 standard deviation (SD)). Slippage was first detected at a torque varying between 2.5 and 8.2 N m (mean, 5.1 N m ± 2.1 SD) in group 2 and between 10.0 and 15.4 N m (mean, 13.0 N m ± 2.3 SD) in group 3. In conclusion the bridging nail offers a stable connection with the stem of a hip arthroplasty which can resist high repetitive loads, representative of direct full axial weight bearing. The biomechanical results support the clinical experience of a stable osteosynthesis enabling early post-operative mobilization.