Migration Pattern of a Cobalt-Chrome Monoblock Acetabular Component after Metal-on-Metal HIP Resurfacing

Abstract

Objectives The purpose of this study was to study the initial fixation and migration pattern of a monoblock acetabular component used for a metal on metal hip resurfacing using Einzel Bild Roentgen Analyse (EBRA). Methods 99 patients with a mean age of 49.6 years (range 28.5-66.3 years) of whom 14 were bilateral underwent a hip resurfacing (Conserve Plus®, MicroPort, Memphis, TN) for a total of 113 resurfacings. Acetabular component orientation was noted with 35 of the 113 components (31.0%) having a lucency >2 mm on the immediate postoperative radiograph. Results The mean follow-up for our cohort of 113 hips is 50 months (2-79 months). When examining the 2-year migration mark, 37 of the 113 hips exceeded the threshold of 0.5 mm/year with a median total migration of 1.40 mm (range 1.02-4.24). 6 resurfacings underwent revision surgery for aseptic loosening of the acetabular component at a mean time of 43.6 months. Presence of initial lucency (OR 2.29, p = 0.05) was the only significant predictor of migration over threshold at 2-years. Those that had migrated over the threshold (1.0 mm) at 2 years were at significantly greater risk of continued migration at 4 years. Conclusions The migration pattern of this component raises concerns about long term performance, with postoperative lucencies representing a significant factor for future migration.