Prognostic value of the sliding length of cephalocervical screws to predict the risk of non-union after osteosynthesis: a retrospective analysis of 86 patients with intracapsular femoral neck fractures

BACKGROUND Here, we assessed the prognostic value of the early sliding length (ESL) for predicting the risk of non-union after internal fixation of femoral neck fractures (FNFs) by Dual SC Screws (DSCS). METHODS A retrospective analysis of 86 patients with intra-capsular FNFs was performed. They underwent osteosynthesis by DSCS at our institution between 2008 and 2013 with a minimum follow-up duration of 6 months. Preoperative displacement, fracture reduction quality, ESL of screws at 2 weeks postoperatively, and correlation of non-union with the ESL of screws were evaluated. RESULTS Bone union without complications was achieved in 74 patients (86.0%), whereas 12 patients (14.0%) showed non-union. The ESL was significantly longer in the non-union group (proximal 3.94 ± 2.79 mm, distal 4.03 ± 3.16 mm) than in the union group (proximal 0.98 ± 1.85 mm, distal 1.01 ± 1.84 mm, P = 0.0001* for proximal, P < 0.0001* for distal). The ESL was significantly associated with non-union, both in the proximal [P = 0.0002, unit odds ratio (OR) 1.58, 95% confidence interval (CI) 1.23-2.16] and distal screws (P = 0.0002, unit OR 1.53, 95% CI 1.21-2.02). The areas under the ROC curves for the ESL of proximal and distal screws were 0.845 and 0.867, respectively; the cut-off values to predict non-union were 1.0 mm (sensitivity 91.7% and specificity 74.3%) and 1.4 mm (sensitivity 83.3% and specificity 81.1%), respectively. CONCLUSIONS In this study, the ESL was a good predictor of postoperative non-union in patients with FNFs fixed by DSCS.