The CCJR® Charles A. Engh, Sr, MD. Excellence in Hip Research Award: Pelvic Tilt and Cup Position Change Significantly in Most Young Patients 10 Years after Hip Arthroplasty

Background: Acetabular cup position is fundamental to total hip arthroplasty (THA) and surface replacement arthroplasty (SRA). Even if initial cup placement is adequate, changes in spinopelvic relationships alter functional acetabular position over time. This can lead to late complications. The purpose of this study was to examine changes in pelvic tilt and acetabular position in patients with at least 10 years of follow-up after THA or SRA. Methods: A retrospective review was conducted of patients from one academic practice who underwent THA or SRA and had at least 10 years of follow-up. Pelvic ratio was measured and converted to pelvic tilt. Changes in pelvic tilt were compared from initial X-rays to final follow-up and between two subgroups based on age. Clinically meaningful changes in pelvic tilt and estimated acetabular position were calculated. Results: There were 200 patients included: 100 aged 45 to 50 years and 100 aged 55 to 60 years. Their mean age was 52 years, 111 were men, and the mean body mass index was 29.7 (range, 18.8 to 49.3). Pelvic tilt change over the 10-year period was −9.87 degrees (SD 10.22), P < 0.001. This corresponds to an increase in acetabular inclination of 1.97 degrees and anteversion of 7.90 degrees. There was meaningful change in 62.5% of patients’ posterior tilt with functional change in version or inclination of > 5 degrees. The subgroup of patients aged 45 to 50 years had a larger change in pelvic tilt (−11.50 degrees, SD 9.04) than patients aged 55 to 60 years (−8.25 degrees, SD 11.01), P = 0.024. Conclusions: We observed increases in posterior tilt in patients 10 years following THA or SRA, resulting in functionally increased acetabular anteversion and inclination. Larger increases in posterior tilt were seen in the younger group, which has implications for initial cup placement in patients with normal spines.