New radiographic parameters to describe anterior acetabular rim trimming during hip arthroscopy

Abstract

Purpose: The purpose of this study was to describe additional radiographic parameters that may detect changes within the acetabular cavity during acetabular rim trimming for pincer-type femoroacetabular impingement.

Methods: Cadaveric hips that met the inclusion criteria were stripped of all tissue and had a portion of their labra removed; 5 mm of anterior acetabulum was measured in the 12- to 3-o'clock position and resected with a Dremel device (Robert Bosch Tool, Mount Pleasant, IL). Anteroposterior radiographs were obtained with a C-arm image intensifier. Radiographic measurements were subsequently obtained using the anterior rim angle (ARA), anterior wall angle (AWA), and anterior margin ratio (AMR).

Results: Statistically significant changes were seen in the ARA, AWA, and AMR. Mean pre- and post-trimming changes were 81.0° and 85.7°, respectively, for the ARA; 34.8° and 29.2°, respectively, for the AWA; and 0.66 and 0.57, respectively, for the AMR.

Conclusions: Although much attention has been focused on the center-edge angle, the anterior aspect of the acetabulum has not previously been characterized. In conjunction with the center-edge angle and Tönnis angle, the new parameters of ARA, AWA, and AMR can be used to provide a more comprehensive description of the acetabulum. The ARA, AWA, and AMR can be used to guide the surgeon intraoperatively and postoperatively in further clarifying acetabular morphology and in determining whether the rim resection was adequate. This study determined that there exist new radiographic parameters with significant changes in the anterior acetabulum as quantified by the ARA, AWA, and AMR that can be used to describe the radiographic changes after acetabular rim resection.

Clinical relevance: The new parameters of ARA, AWA, and AMR can be used to provide a more comprehensive description of the acetabulum. These radiographic measurements can also be used by hip arthroscopists to better describe their surgical contribution to anterior rim trimming.