Background: The modified Dunn procedure (MDP) has become popular during the last 16 years to treat severely displaced slipped capital femoral epiphysis (SCFE) while "in situ" pinning (ISP) has remained valid to treat mild to moderate SCFE, although the indication limit of the Southwick angle (SA) has not yet been established for either procedure. In this context, we reviewed two cohorts of patients with SCFE, one treated by ISP and the other by MDP. We also tried to better elucidate the etiopathogenesis of hip instability, a severe complication of MDP.
Methods: Fifty-one consecutive patients with 62 hips affected by SCFE were treated by us from 2015 to 2019: 48 hips with a SA ≤ 40° had ISP while 14, with the SA > 40°, had MDP. The latter also had a CT scan to better investigate the SCFE morphology. Results were assessed using the Harris Hip Score.
Results: The mean length of follow up of the two cohorts was 5.4 years (range: 3 to 8 years). Of the 35 hips operated by ISP with a full follow-up evaluation, 30 had an excellent or good result, 3, fair, and 2, poor. Of the 14 hips that underwent MDP, 11 had an excellent or good result, 1, fair, and 2, poor. A CT scan showed femoro-acetabular incongruency in two unstable hips following MDP.
Conclusions: We performed ISP in chronic SCFE with the SA ≤ 40° and MDP in acute and chronic SCFE with the SA > 40°, with satisfactory results. In both acute-on-chronic and chronic long-lasting SCFE with severe displacement, planned for MDP, a CT scan should be carried out to evaluate possible femoro-acetabular incongruency that may cause hip instability.
Keywords: Hip instability (HI) following modified Dunn procedure (MDP); Hip remodeling after in situ pinning; In situ pinning (ISP); Modified Dunn procedure (MDP); Pathogenesis of hip instability (HI); Slipped capital femoral epiphysis (SCFE).