Unique stability of femoral neck fractures treated with the novel biplane double-supported screw fixation method: A biomechanical cadaver study

Osteosynthesis of femoral neck fractures is related to 20-46% complication rate. Filipov's novel method for biplane double-supported screw fixation (BDSF), using three cannulated screws, has demonstrated excellent clinical results since 2007. Its two calcar-buttressed screws are oriented in different coronal inclinations with steeper angles to the diaphyseal axis and intended to provide constant fixation strength under different loading situations.The aim of this study was to biomechanically evaluate BDSF fixation strength and compare it with the conventional fixation (CFIX) using three parallel cannulated screws.MethodsEight fresh-frozen and six embalmed human femoral pairs with simulated AO/OTA31-B2.2 fracture were fixed applying either CFIX or BDSF. Quasistatic tests were performed in anteroposterior (AP) bending, followed by axial quasistatic, cyclic and destructive quasistatic tests run in 10° flexion with 7° or 16° varus specimen inclination.ResultsInitial axial stiffness was significantly higher for BDSF in comparison with CFIX at 7° inclination (p = 0.02) and not significantly different between BDSF and CFIX at 16° inclination. Compared with the intact state, it decreased significantly at 7° inclination only for CFIX (p = 0.01), but not for BDSF. Interfragmentary displacement during cyclic testing was significantly smaller for BDSF than CFIX at 7° inclination (p ≤ 0.04) and not significantly different between BDSF and CFIX at 16° inclination. Failure load did not differ significantly between BDSF and CFIX at both inclinations.ConclusionsFemoral neck fracture stability can be substantially increased applying BDSF due to better cortical screw support and screw orientation. Having two calcar-buttressed screws oriented in different inclinations, BDSF can enhance constant stability during various patient activities. The more unstable the situation, the better BDSF stability is in comparison to CFIX.