Correlation Between Radiographic Parameters and Clinical Range of Motion in Slipped Capital Femoral Epiphysis.

Abstract

Background: Surgical procedures that improve motion for slipped capital femoral epiphysis (SCFE) deformity are typically guided by radiographic imaging. However, the specific aspects of the deformity that have the greatest impact on hip functional biomechanics remain unclear. This study investigated the relationship between radiographic parameters and clinical ROM measurements in patients with SCFE to better elucidate which elements of SCFE pathoanatomy have the greatest effect on joint mobility.

Methods: Patients who underwent in situ pinning for stable SCFE at a single institution between 2013 and 2025 were retrospectively reviewed. Patients were excluded if they had unstable SCFE or underwent a modified Dunn osteotomy or simultaneous bilateral SCFE procedures. Demographics and clinical ROM measurements were obtained from the electronic health record. Radiographic parameters, including the Southwick slip angle (SSA), posterior sloping angle (PSA), percent epiphyseal displacement of Wilson (PED), and alpha angle, were measured on immediate postoperative radiographs. ROM deficits were calculated as the difference between affected and unaffected hips. The relationships between radiographic and clinical ROM variables were quantified using linear regressions.

Results: Seventy-four hips in 69 patients (mean age 12.3±1.5 y, 50.7% male) were included. In 5 patients, ROM data were available for the contralateral, unaffected hip just before a subsequent slip and were used as control measurements for that hip. Overall, PED had the largest effect on ROM. For every 1% increase in displacement, patients lost an average of 2.18 degrees of flexion ( P <0.001) and 2.13 degrees of abduction ( P =0.001). SSA, PSA, and AP alpha angle had statistically significant effects on internal rotation in flexion (IRF)-a 1-degree increase in each led to a 0.78, 0.81, and 0.74-degree decrease in IRF, respectively ( P <0.001 for all). The lateral alpha angle had the smallest impact.

Conclusions: In children with SCFE, radiographic deformity predicts clinical ROM. PED has the strongest negative association with flexion and abduction, while PSA, SSA, and AP alpha angle have negative associations with IRF. Reconstructive strategies should prioritize correction of these aspects of the SCFE deformity to maximize joint mobility.

Level of evidence: Level III-retrospective comparative study.