Model to Predict Need for Subtrochanteric Shortening Osteotomy During Total Hip Arthroplasty for Crowe Type IV Developmental Dysplasia

BACKGROUND: Indications for subtrochanteric shortening osteotomy (SSOT) during Crowe type IV developmental dysplasia of the hip (DDH) are unclear. The aim of this retrospective study was to create a model to predict the need for performing SSOT. MATERIAL/METHODS: One hundred forty-nine patients (186 hips) with Crowe Type IV DDH who underwent total hip arthroplasty (THA) with S-ROM implants from January 2010 to November 2018 were included in the study. The acetabular components were placed at the true acetabulum and the trial femoral component was inserted. Reduction then was attempted and if it could not be achieved, SSOT was performed. Using multivariable Cox regression analysis, a model was constructed that included age, sex, surgical history, use of a cone- or triangle-shaped sleeve, secondary acetabulum formation, and percentage of dislocation as predictive factors for SSOT. RESULTS: SSOTs were performed on 140 of 186 hips. Secondary acetabulum formation was present in 27 hips (58.70%) in which SSOT was not performed 7 (5.00%) in which it was performed. Cone-shaped sleeves were used in 17 hips (36.96%) in which SSOT was not performed versus 15 (10.71%) hips in which it was performed. Dislocation occurred in 31.30±5.80% hips in which SSOT was performed versus 24.05±4.39% of those in which it was not performed. Percentage of dislocation was associated with an increased likelihood of SSOT (odds ratio [OR] 1.24, 95% confidence interval 1.11–1.38), whereas secondary acetabulum formation (OR 0.10, 0.03–0.33) and use of a cone-shaped sleeve (0.18, 0.06–0.53) were associated with decreased likelihood of SSOT. We established a model for prediction of SSOT with a nanogram and the discriminative ability (C statistic) of it was 0.918 (0.79–0.92). CONCLUSIONS: Factors that significantly affect likelihood of performing an SSOT were identified and a model with significant ability to predict the need for SSOT in patients with Crowe Type IV DDH was created.