Abstract
Introduction
Most metal-on-metal hip resurfacing implants currently being used worldwide utilize bone ingrowth fixation on the acetabular side, but cement fixation remains the standard method of fixation on the femoral side. Our hypothesis is that bone ingrowth fixation of a fully porous-coated component is superior to cement fixation of the femoral hip resurfacing component.
Methods
From March 2007 to Jan 2009, 429 consecutive metal-on-metal hip resurfacing arthroplasties were performed by a single surgeon in 396 unselected patients using Biomet uncemented femoral and acetabular components. All of these were at least 5-years postop. Three patients died with causes unrelated to their hip arthroplasty. The three most common primary diagnoses were osteoarthritis in 318 (74%) cases, dysplasia in 66 (15%) hips, and osteonecrosis in 19 (4%) hips. The average size of the femoral component was 50 ± 4 cm. All pre-operative, intra-operative, and post-operative data were prospectively collected and entered into our database for review. All patients are allowed unrestricted activity including impact sports after 6 months.
Results
Metal ion test results were available for 78% of patients. There were 14 (3.2%) failures identified at the time of this study. There were six (1.4%) early femoral failures (4 femoral neck fractures, 2 head collapses prior to 2 years), four loose acetabular components (one failed at 2 months postoperatively; three after 2 years), two (0.5%) adverse wear related failures (AWRF; metal ion levels ≥10 ug/L, AIA> 500, metalosis), one intertrochanteric fracture; and one failure due to subluxation. There were no cases of failure of femoral ingrowth or late femoral loosening. For the non-failed group, the average post-operative HHS score was 97±9 at their latest follow-up; the average UCLA Activity Score was 7±2. Survivorship was 96.7% at 5 years (all failures). Femoral survivorship was 98.4%. The AWRF rate was 0.5% at 5 years. No femoral failures occurred after one year postop up to 7 years.
Conclusions
Bone ingrowth fixation with a fully porous femoral component in hip resurfacing remains highly durable beyond 5 years. Femoral ingrowth is more reliable than acetabular ingrowth. No cases of femoral loosening have been encountered up to 7 years post implantation. AWRF is rare (0.5% at 5 years) and is caused by acetabular component malposition.
