Increased migration of uncemented acetabular cups in female total hip arthroplasty patients with low systemic bone mineral density

Background and purpose — Low bone mineral density (BMD) may jeopardize the initial component stability and delay osseo- integration of uncemented acetabular cups in total hip arthro- plasty (THA). We measured the migration of uncemented cups in women with low or normal BMD. Patients and methods — We used radiostereometric analysis (RSA) to measure the migration of hydroxyapatite-coated tita- nium alloy cups with alumina-on-alumina bearings in THA of 34 female patients with a median age of 64 (41–78) years. 10 patients had normal BMD and 24 patients had low systemic BMD (T-score ≤ −1) based on dual-energy X-ray absorptiometry (DXA). Cup migration was followed with RSA for 2 years. Radiographic fol- low-up was done at a median of 8 (2–10) years. Results — Patients with normal BMD did not show a statis- tically significant cup migration after the settling period of 3 months, while patients with low BMD had a continuous proximal migration between 3 and 12 months (p = 0.03). These differences in cup migration persisted at 24 months. Based on the perceived risk of cup revision, 14 of the 24 cases were “at risk” (proximal translation of 0.2 to 1.0 mm) in the low-BMD group and 2 of the10 cases were “at risk” in the normal-BMD group (odds ratio (OR) = 8.0, 95% CI: 1.3–48). The radiographic follow-up showed no radiolucent lines or osteolysis. 2 cups have been revised for frac- tures of the ceramic bearings, but none for loosening. Interpretation — Low BMD contributed to cup migration beyond the settling period of 3 months, but the migrating cups appeared to osseointegrate eventually.