Screw Thread Configuration Has No Effect on Outcomes of In Situ Fixation for Stable Slipped Capital Femoral Epiphysis.

Background: No consensus exists regarding the optimal surgical management of slipped capital femoral epiphysis (SCFE). Treatment goals include avoiding slip progression and sequelae such as avascular necrosis (AVN). Factors associated with surgical implants merit further research. This study investigates the effect of screw thread configuration and the number of screws on surgical outcomes.

Methods: A total of 152 patients undergoing cannulated, stainless steel, in situ screw fixation of SCFE between January 2005 and April 2018 were included. Procedure laterality, screw number and thread configuration (partially threaded/fully threaded), bilateral diagnosis, Loder classification, final follow-up, patient demographics, and endocrinopathy history were analyzed. Primary outcomes were return to the operating room (ROR), AVN, hardware failure/removal, and femoroacetabular impingement (FAI).

Results: Most patients received a single (86.2%), partially threaded (81.6%) screw; most were unilateral (67.8%) and stable (79.6%). Mean follow-up was 2.0±2.7 years, with a 15.8% rate of ROR, 5.3% exhibiting AVN, 6.6% exhibiting FAI, and 9.2% experiencing hardware failure/removal. Number of screws was the sole predictor of ROR [odds ratio (OR)=3.35, 95% confidence interval (CI): 1.18-9.49]. Unstable SCFE increased the odds of AVN (OR=38.44; 95% CI: 4.35-339.50) as did older age (OR=1.43, 95% CI: 1.01-2.03). Female sex increased risk for FAI (OR=4.87, 95% CI: 1.20-19.70), and bilateral SCFE elevated risk for hardware failure/removal versus unilateral SCFE (OR=4.41, 95% CI: 1.39-14.00). Screw thread configuration had no significant effect on any outcome (for each, P ≥0.159).

Conclusions: Rates of ROR, AVN, FAI, and hardware failure/removal did not differ between patients treated with partially threaded or fully threaded screws. The use of 2 screws was associated with an increased likelihood of ROR. These findings suggest that screw thread configuration has no impact on complication rates, whereas screw number may be an important consideration in SCFE fixation.

Level Of Evidence: Level III-retrospective cohort study.