Is anterosuperior cup overhang a risk factor for iliopsoas impingement after total hip arthroplasty? A radar chart analysis

Groin pain is an occasional complication of total hip arthroplasty (THA), with iliopsoas impingement (IPI) often associated with irritation between the iliopsoas tendon and an overhanging acetabular cup. Although cup overhang is typically assessed using radiography or computed tomography (CT), a more precise evaluation of cup positioning within the acetabulum may improve IPI diagnosis. This study aimed to investigate the association between IPI and circumferential cup overhang using the radar chart method to determine the precise amount of cup overhang without being affected by the metal artifacts. A total of 128 patients who underwent primary THA via the direct anterior approach between 2014 and 2023 were analyzed. Patients were divided into IPI and non-IPI groups. To eliminate the influence of metal artifacts, pre-operative CT with a computer-aided design model of the acetabulum cup was generated using image matching. Radial CT planes were created at 15° intervals, and the angles of edge of the acetabular cup (ACA) and acetabular rim (ARA) were measured in each plane. The acetabular rim was represented as a clock, and radar charts were generated for each group. Cup overhang was defined as locations where the ACA exceeded the ARA. The radar chart of the IPI group demonstrated significant cup overhang in the 1:30 location. These result suggests that cup overhang in the anterosuperior region, particularly in the 1:30 location, is a risk factor for IPI following THA. The radar chart method provides a comprehensive evaluation of cup positioning and may serve as a valid evaluation tool for assisting IPI diagnosis. • Cup overhang at 1:30 in the anterosuperior area may cause iliopsoas impingement (IPI) after total hip arthroplasty. • Radar chart provides a novel method for precise cup overhang assessment in all directions. • Ensuring adequate acetabular coverage of the cup at 1:30 location is key to preventing IPI. • Larger cohorts are required to define the cutoff value for IPI diagnosis with the radar chart.