Femoral Neck Growth and Remodeling With Free-Gliding Screw Fixation of Slipped Capital Femoral Epiphysis

Background: Treatment of stable slipped capital femoral epiphysis (SCFE) most commonly involves in situ fixation with a standard cannulated screw, leading to physeal arrest. Recently, Pega Medical (Laval, Canada) introduced the free-gliding (FG) SCFE screw, which employs a growth-friendly, telescopic design. This study examines femoral neck growth and remodeling over the first 2 postoperative years in stable SCFE treated with FG versus standard screws. Methods: We retrospectively reviewed 32 hips (19 SCFE, 13 prophylactic) in 16 patients treated with FG screws for stable SCFE. We also reviewed 102 hips (63 SCFE, 19 prophylactic, 20 controls) in 55 patients treated with standard screws. Immediate postoperative radiographs were compared with 1- and 2-year follow-up images. Results: For the overall study cohort, mean age at surgery was 12.2 +/- 1.9 years, with a mean slip angle of 26.9 +/- 18.0 degrees. In FG SCFE hips, the alpha angle remodeled 12.9 +/- 19.2 degrees in the first postoperative year (P=0.018) and articulotrochanteric distance decreased by 4.2 +/- 4.6 mm at 2 years (P=0.018). In standard SCFE hips, the alpha angle remodeled 4.3 +/- 11.3 degrees at 1 year (P=0.014), while articulotrochanteric distance decreased by 4.5 +/- 3.2 mm at 2 years (P<0.001). By 2 years, FG screws lengthened more in prophylactic (4.8 +/- 3.4 mm) than SCFE hips (1.7 +/- 1.8 mm, P=0.027). Conclusions: Greater remodeling of femoral neck cam deformity occurs when treating SCFE using an FG screw. Further research is required to measure the impact of this finding on femoroacetabular impingement and degenerative arthritis. In addition, FG screws allow ongoing growth of prophylactically treated hips, while standard screws promote coxa breva.