More than 20° posterior tilt of the femoral head in undisplaced femoral neck fractures results in a four times higher risk of treatment failure.

PURPOSE In this study, we aimed to determine the correlation between the preoperative posterior tilt of the femoral head and treatment failure in patients with a Garden type I and II femoral neck fracture (FNF) treated with the dynamic locking blade plate (DLBP). METHODS Preoperative posterior tilt was measured in a prospective documented cohort of 193 patients with a Garden type I and II FNF treated with the DLBP. The correlation between preoperative posterior tilt and failure, defined as revision surgery because of avascular necrosis, non-union, or cut-out, was analyzed. RESULTS Patients with failed fracture treatment (5.5%) had a higher degree of posterior tilt on the initial radiograph than the patients with uneventful healed fractures: 21.4° and 13.8°, respectively (p = 0.03). The failure rate was 3.2% for Garden type I and II FNF with a posterior tilt < 20° and 12.5% if the preoperative posterior tilt was ≥ 20°. A posterior tilt of ≥ 20° was associated with an odds ratio of 4.24 (95% CI 1.09-16.83; p = 0.04). CONCLUSION Garden type I and II FNFs with a significant preoperative posterior tilt (≥ 20°) seem to behave like unstable fractures and have a four times higher risk of failure. Preoperative posterior tilt ≥ 20° of the femoral head should be considered as a significant predictor for failure of treatment in Garden type I and II FNFs treated with the DLBP.