Does Replicating Native Hip Biomechanics Improve Patient-Reported Outcome Measures After Total Hip Arthroplasty?

Background: Enabling technology, such as computer navigation and robotics, provides more precise implant position, which allows surgeons the ability for personalized alignment in total hip arthroplasty (THA). To date, THA implant position studies have focused on dislocation rates, rather than on patient-reported outcome measures (PROMs). This study evaluated the impact of the THA component position on clinically significant differences in PROMs.

Methods: A total of 1,682 consecutive primary THAs were retrospectively reviewed. Acetabular and femoral component position as well as femoral offset and leg length discrepancy (LLD) were measured on all preoperative and postoperative radiographs. Modern PROM scores were evaluated. Minimal clinically important difference (MCID), substantial clinical benefit (SCB), and patient-acceptable symptom state (PASS) values were assessed for applicable PROMs. Univariate and multivariate statistical analyses were performed with P < 0.05 as significant. The mean clinical follow-up was 21.9 months (range, one to 128).

Results: In multivariate analysis, the acetabular component position closer to the native hip center of rotation was associated with a greater probability of achieving the Hip disability and Osteoarthritis Outcome Score for Joint Replacement (HOOS JR), MCID, SCB, and PASS thresholds (P ≤ 0.008). An increase in postoperative femoral offset was associated with achieving the MCID for the University of California Los Angeles (UCLA) activity level and patients being 'very satisfied or satisfied' (P ≤ 0.004). The mean postoperative LLD was 3.8 mm (range, 24.5 mm short to 36.6 mm long); however, postoperative LLD was NOT a predictor of PROMs (P ≥ 0.167) with statistical power ≥ 87%.

Conclusion: Study results demonstrated that replicating the native center of rotation and optimizing femoral offset was associated with clinically relevant improvements in PROMs. Interestingly, in this large cohort, leg-length inequality was not associated with PROMs. Further research is warranted on THA component position, including spino-pelvic parameters and PROMs.