Association between total hip arthroplasty following periacetabular osteotomy and acetabular component overhang.

Abstract

There is limited understanding of anterior acetabular component overhang, which induces groin pain, in post-periacetabular osteotomy (PAO) hips during conversion to total hip arthroplasty (THA). The aim of the study were to determine the following: (1) the differences in the amount of acetabular component overhang among pre-PAO hips and post-PAO hips in simulating THA; (2) the factors associated with the amount of component overhang in THA following PAO; (3) whether high component placement with elevation of the hip center by 10mm reduces the amount of component overhang compared to the anatomical component position in THA following PAO. Computer-based simulations of acetabular component implantation were performed using preoperative and postoperative CT data from 30 patients undergoing PAO. Implantation was performed thrice in each patient: in pre-PAO hips (anatomical component position) and post-PAO hips (anatomical and high component position). Component overhang was measured on the axial plane, which passes through the component center. Overhang was greater in post-PAO hips [mean (SD) overhang: 5.2 (2.9) mm, pre-PAO hips: 10.2 (4.6) mm, post-PAO hips-mean difference, 5.0mm; p < 0.001]. A smaller distance between the pubic osteotomy and the acetabulum, and greater overhang in pre-PAO hips was independent factors associated with increased overhang in post-PAO hips. Overhang was smaller with the high component position than with the anatomical component position in post-PAO hips [mean (SD) overhang-3.5mm (2.9) with high component position among post-PAO hips; mean difference, 6.6mm; p < 0.001). Ten post-PAO hips with the anatomical component position had overhang of at least 12mm (the likely threshold for groin pain). Of these, 9 hips had reduced overhang (< 12mm) with the high component position. Acetabular component overhang was more severe in THA following PAO than in THA without prior PAO. Pubic osteotomy should be performed closer to the acetabular rim to prevent severe overhang in potential THA conversion cases. A high component position decreased the risk of severe overhang.