What makes fixation of femoral neck fractures fail? A systematic review and meta-analysis of risk factors

•Female, ≥50 years, smoking, inadequate reduction and treatment with cannulated screws are predictors for reoperation in patients with dFNF.•Female patients with a dFNF above 50 years of age that smoke have a high risk of failure of treatment.•The results of this study can be used to substantiate future algorithms and guidelines for treatment of dFNF. This systematic review aims to provide an overview of predictors for failure of treatment of displaced femoral neck fracture (dFNF) with internal fixation and quantify their risk of fixation failure in a meta-analysis. PubMed, Embase, Web of Science, Cochrane Library, and EMCare were searched for original studies published from January 2000, including adult patients with an internally fixated dFNF, that reported data on predictors for fixation failure defined as revision surgery due to non-union, avascular femoral head necrosis or cut-out of implant. RevMan version 5 software was used to pool univariable Odds Ratio's (OR) for predictors of fixation failure by means of a random effects model. This review included 16 articles (15 articles cohort studies and one randomised trial). Twenty-four predictors for fixation failure were identified and analysed, 16 of which were evaluated in just one study. Data of 7 predictors were pooled in a meta-analysis. Female sex (OR 1.78, 95% confidence interval [CI] 1.26–2.52), smoking (OR 3.64, 95% CI 1.68–7.91), age >50 years (OR 3.64, 95% CI 1.68–7.91), inadequate fracture reduction (OR 2.28, 95% CI 1.62–3.22), fixation with cannulated screws (CS) or pins compared to fixed angle devices (OR 2.16, 95% CI 1.03–4.54) were identified as significant predictors for fixation failure. This study can help surgeons to choose the preferred treatment for patients with a dFNF and substantiate future algorithms and guidelines for treatment of FNF.