RESUMEN
INTRODUCTION: Cadaveric models have demonstrated a high incidence of extraosseous "in-out-in" (IOI) posterosuperior screws after cannulated screw fixation of femoral neck fractures. The purpose of this study was to determine the incidence of IOI screws in vivo and to evaluate their association with osteonecrosis and revision surgery. METHODS: A total of 104 patients with 107 hips with a pelvis computed tomography (CT) scan after cannulated screw fixation of a femoral neck fractures were included. Screw position was evaluated on postoperative radiographs and CT scan to determine if screws were IOI or all-in. Osteonecrosis and revision surgeries were documented. RESULTS: IOI posterosuperior screws were identified on CT scan in 58 (54%) hips. On postoperative AP and lateral radiographs, IOI screws were a median (interquartile range) of 10 mm (7-11 mm) and 3 mm (0-4 mm) from the cortex, respectively. The sensitivity and specificity of radiographs to detect IOI screws was 39% and 92%, respectively. The incidence of osteonecrosis and revision surgeries in hips, with and without IOI screws, was 6% versus 6% [Odds ratio (OR) 1.1, 95% confidence interval (CI) 0.2-5.3] and 10% versus 10% (OR 1.0, CI 0.3-3.1), respectively; a true clinical difference cannot be excluded due to the width of the confidence intervals. CONCLUSIONS: There was a high incidence of IOI posterosuperior screws on CT scans. Postoperative radiographs had a poor sensitivity for detecting IOI screws. A larger sample size is necessary to evaluate the association of IOI screws with osteonecrosis and revision surgery. LEVEL OF EVIDENCE: Level III, comparative cohort study.