Impact of functional evaluation 3D software on impingement and clinical outcomes in robotic-arm assisted total hip arthroplasty

Background: This study aims to investigate whether individualized component positioning in robotic-assisted total hip arthroplasty (RTHA) using three-dimensional (3D) Functional Component Positioning Assessment (FCPA) reduces prosthetic and bone impingement and improves Patient-Reported Outcome Measures (PROMs). Methods: This retrospective study includes 100 consecutive patients who underwent RTHA at a single center between May 2021 and March 2022 using the Mako THA system. Preoperative imaging and planning incorporated sacral slope (SS) measurements. SS values in standing and sitting positions were uploaded into the robotic software to simulate prosthetic hip motion during FCPA and guide component orientation. The primary outcome measures included intraoperative impingement analyses using FCPA and postoperative PROMs, including the Oxford Hip Score (OHS), Forgotten Joint Score (FJS-12), and Hip Disability and Osteoarthritis Outcome Score (HOOS). Results: Impingement was detected in 46% of patients during daily living activities, with prosthesis-on-prosthesis being the most frequent impingement type. No statistically significant differences in PROMs were observed between patients with and without impingement. Nonetheless, overall PROMs were excellent, with a mean HOOS of 94.2 ± 8.3, mean FJS-12 of 87.8 ± 17.2, and mean OHS of 92.3 ± 10. Multivariate analysis revealed that higher BMI negatively impacted PROMs, and the SS difference correlated significantly with OHS and FJS-12 scores (P < 0.0001). Conclusions: Individualized component positioning, even when aided by 3D FCPA, does not eliminate the risk of impingement. The concept of a universal “safe zone” may be inadequate to prevent impingement, emphasizing the need for patient-specific implant positioning strategies based on spinopelvic mobility. While impingement did not significantly impact PROMs, optimizing implant positioning through robotic-assisted techniques may contribute to improved long-term outcomes and reduced dislocation risk.