Who Benefits From Allowing the Physis to Grow in Slipped Capital Femoral Epiphysis?

ABSTRACT

BACKGROUND: The globally acknowledged treatment for mild to moderate slipped capital femoral epiphysis (SCFE) is single screw in situ fixation, also used for prophylactic contralateral fixation. The Free-Gliding Screw (FG; Pega Medical) is a 2-part free-extending screw system designed to allow the growth of the proximal femur. We aimed to analyze the relationship between skeletal maturity and potential growth of the proximal physis and remodeling of the femoral neck using this implant. MATERIALS AND METHODS: Females below 12 years and males below 14 years undergoing in situ fixation for stable SCFE or prophylactic fixation were treated using the implant. Three elements of the modified Oxford Bone (mOB 3 ) score were used to measure maturity (triradiate cartilage, head of the femur, and greater trochanter). Radiographs were analyzed immediately postoperatively and at a minimum of 2 years for a change in screw length, posterior-sloping angle, articulotrochanteric distance, α angle, and head-neck offset. RESULTS: The study group comprised 30 (FM=1218) of 39 hips treated with SCFE and 22 (FM=139) of 29 hips managed prophylactically using the free-Gliding screw. In the therapeutic group, chronologic age was a less valuable predictor of future screw lengthening than mOB 3 . An mOB 3 of ≤13 predicted future growth of >6 mm but did not reach statistical significance ( P =0.07). Patients with open triradiates showed a mean screw lengthening of 6.6 mm compared with those with closed triradiates (4.0 mm), but this did not reach significance ( P =0.12). In those with mOB 3 ≤13, the α angle reduced significantly ( P <0.01) and the head-neck offset increased significantly, suggesting remodeling. There was no change in these parameters when mOB 3 ≥14. In the prophylactic group, change in screw length was significant with mOB 3 of ≤13 (mean=8.0 mm, P <0.05), as was the presence of an open triradiate cartilage (mean=7.7 mm, P <0.05). In both cohorts, posterior-sloping angle and articulotrochanteric distance did not change, indicating no slip progression in either treatment or prophylactic groups and minimal effect on the proximal physeal growth relative to the greater trochanter. CONCLUSIONS: Growing screw constructs can halt slip progression while allowing proximal femoral growth in young patients with SCFE. Ongoing growth is better when the implant is used for prophylactic fixation. The results in treated SCFE need to be expanded to demonstrate a clinically meaningful cut-off for significant growth, but SCFE patients with an open triradiate remodel significantly more than those where it is closed. LEVEL OF EVIDENCE Level III-retrospective comparative study.