Investigation of the Frequency, Location, and Impact on Postoperative Outcomes of Osseous Impingement in Preoperative Planning Using Mako Total Hip Arthroplasty Version 4.0

The Mako THA ver4.0 enables simulation of implant-to-implant impingement angles during preoperative planning, optimizing cup anteversion based on stem design, alignment, and femoral head size. Osseous impingement detection has also become possible, but its integration into planning remains unclear. This study evaluated the frequency, location, and postoperative impact of non-osteophyte osseous impingement using ACCOLADE II stems and the VROM feature. Cup angles were adjusted to avoid implant impingement in four positions: 120° flexion, 40° extension, 90° flexion with 40° internal rotation, and 40° external rotation. Osteophyte-related impingement was addressed intraoperatively. A total of 82 patients (106 hips) undergoing cementless THA using Mako THA ver4.0 between September 2020 and May 2023 were included. The cohort had 67 females and 15 males, aged 43–83 years (mean 67). CT-based preoperative planning aimed to equalize leg length and offset. The cup inclination was fixed at 40°, and anteversion was adjusted with VROM. Non-osteophyte osseous impingement was assessed, and its relationship to postoperative WOMAC scores was analyzed. Over a mean follow-up of 3 years, the JOA hip score improved significantly from 57 to 97, and WOMAC improved from 41 to 6. No dislocations occurred. Non-osteophyte impingement was observed in 26 hips (25%) during flexion or internal rotation (AIIS and femoral neck) and in 33 hips (31%) during extension or external rotation (ischium and femur). These cases showed no impact on clinical scores. This study is the first to clarify osseous impingement frequency and locations during preoperative planning with Mako THA ver4.0. Although impingement was observed in 25–31% of cases, it did not affect outcomes, suggesting that minor adjustments in planning effectively mitigate this phenomenon.