Mid-term migration of a cementless, porous acetabular cup: A 5 year radiostereometric analysis

Purpose The aim of the study was to determine the 5-year migratory and wear patterns, adverse events and clinical outcomes of a cementless, porous acetabular cup. Methods RSA imaging of a cohort of 11 patients was retrospective analysed at 5-years post Total Hip Arthroplasty (THA). Changes in pain, function and symptoms of the hip at 5-years post THA were compared to preoperative and 2-year postoperative assessments on the Harris Hip Score (HHS) and Hip Disability and osteoarthritis outcome score (HOOS). Results The majority of cup migration occurred up to 6-months and stabilised thereafter (6-months to 5-years, p=0.091–0.866, Wilcoxon Signed Rank test). The direction of rotation around the 3 axes was evenly distributed among the cups between anterior-posterior rotation, internal-external rotation and increased-decreased inclination. The majority of the cups translated proximally, at an average migration of 0.36 mm (± 95%CI 0.17) at 5-years post THA. Following initial bedding in, up to 6-months, there was no detectable polyethylene wear between 6-months and 5-years. At 5-years postoperatively, a statistically significant difference was observed across all HOOS subscales in comparison to preoperative values, with higher means reported at 5-years (p<0.001). The total mean HHS displayed a statistically significant improvement, increasing from ‘poor’ preoperatively to ‘good’ at 5-years post THA. Conclusion Following initial migration between discharge and 6-months, the cementless porous acetabular cup demonstrated a tendency for stabilisation from 6-months up to 5-years post THA, suggesting good mid-term fixation. Additionally, improvements in clinical outcome measures of pain, function and quality-of-life remained high following THA at 5-years post-surgery.