Association of Relative Skeletal Immaturity of the Triradiate Cartilage with Increased Proximal Femoral Deformity in Prophylactic Fixation for Slipped Capital Femoral Epiphysis: A Radiographic Study.

INTRODUCTION: The purpose of this study was to describe proximal femoral deformity after contralateral hip prophylactic fixation of slipped capital femoral epiphysis (SCFE) in patients and the association of relative skeletal immaturity with this deformity.

METHODS: A retrospective review of patients presenting with a SCFE was conducted from 2009 to 2015. Inclusion criteria were (1) radiographic evidence of a unilateral SCFE treated with in situ fixation, (2) contralateral prophylactic fixation of an unslipped hip, and (3) at least 3 years of follow-up. Measurements were made on radiographs and included greater trochanter height relative to the center of the femoral head, femoral head-neck offset, and femoral neck length. Skeletal maturity was evaluated by assessing the status of the proximal femoral physis and triradiate cartilage (TRC) of the hip, in addition to the length of time to closure of these physes. Values were compared from initial presentation to final follow-up. Statistical analysis included descriptive statistics and linear regression.

RESULTS: Twenty-seven patients were included. Bivariable linear regression demonstrated that an increased relative trochanteric overgrowth was associated with TRC width (β = 3.048, R = 0.585, P = 0.001) and an open TRC (β = -11.400, R = 0.227, P = 0.012). Time to proximal femoral physis closure (β = 1.963, R = 0.444, P = 0.020) and TRC closure (β = 1.983, R = 0.486, P = 0.010) were predictive of increased deformity. In addition, multivariable elimination linear regression demonstrated that TRC width (β = 3.048, R = 0.585, P = 0.001) was predictive of an increased relative trochanteric overgrowth.

DISCUSSION: Patients with an open TRC and increased TRC width are associated with increased relative trochanteric overgrowth when undergoing prophylactic fixation for a unilateral SCFE. Increased caution should be exercised when considering contralateral hip prophylactic fixation in skeletally immature patients presenting with a unilateral SCFE.

LEVEL OF EVIDENCE: Level IV, case series.