Shelf acetabuloplasty may inhibit range of motion: A computer simulation analysis.

Shelf acetabuloplasty has been performed in patients with developmental dysplasia of the hip (DDH); however, the appropriate position of the shelf has not been determined, particularly with respect to avoiding range of motion (ROM) loss. The aim of this study was to investigate the frequency of ROM inhibition and the influence of 3D position of the shelf following actual shelf acetabuloplasty and virtual surgery using computer simulation analysis. CT data from 15 patients with DDH who underwent shelf acetabuloplasty were collected between August 2019 and February 2022. 3D models of a hip joint were constructed using Zed Hip®︎. Maximal internal rotation (MIR) at 45° and 90° flexion was measured in each patient. The frequency and position of ROM inhibition was determined in a real postoperative model virtually. In addition, a second analysis using virtual acetabuloplasty was performed. Upon placing the shelf, three patterns were provided for the following four parameters: height, coronal inclination, center-edge angle (CEA), and anteroposterior position. The predictors for ROM inhibition were analyzed using a logistic regression model.　In the actual postoperative model, a limitation of MIR at 90° and 45° of flexion occurred in 60% and 66.7% of patients, respectively. A higher CEA and anterior position are major factors limiting MIR. The analysis of the virtual shelf acetabuloplasty model revealed that anterior position and CEA were significant factors causing ROM inhibition. As for clinical significance, the results of the current study indicated the optimal location of the shelf to avoid iatrogenic impingement after shelf acetabuloplasty. This article is protected by copyright. All rights reserved.