The outcome of Charnley low-friction arthroplasty in young patients with particular reference to underlying disease process and acetabular wear
A consecutive series of 280 Charnley low-friction arthroplasties, performed between 1966 and 1978, on 192 patients, who were less than 40 years of age at the time of operation, were followed up for an average duration of 20.1 years. Patients were divided into four groups based on underlying disease process, and only three patients (5 hips) could not be traced. Patients with rheumatoid arthritis had significantly lower rates of acetabular component loosening, migration and revision (all p< 0.05), and patients with developmental dysplasia of the hip had the highest rates as well as a significantly higher rate of combined clinical and radiological component failure (p < 0.05). Patients with degenerative arthrosis had the highest rates of femoral implant loosening, revision and failure (all p < 0.05), and patients with ankylosing spondylitis and rheumatoid arthritis had the lowest. Age (< 30 years or 30 to 40 years at operation), gender, heterotopic ossification, hypertrophy of the femoral cortex at the tip of the prosthesis or development of changes in the medial femoral calcar were not associated with an increased risk of component failure or revision (all p > 0.05). The average annual rate of wear of revised components, in each of the four groups and the series as a whole, was significantly higher than the rate in surviving original components (p < 0.04), and the development of osteolysis, and increasing wear of the acetabular component were associated with failure and revision of both the acetabular and femoral components (both p < 0.01). Cox regression analysis confirmed that increasing average annual acetabular wear was the most significant factor determining the outcome of the arthroplasty (p < 0.001). For each additional millimetre of wear observed, the risk of component failure or revision in any one year increased significantly (p < 0.02). The 25-year survivorship of implants with an average acetabular wear rate of less than 0.1 mm/yr (117 arthroplasties) was greater than 90% but no arthroplasties with a rate in excess of 0.2 mm/yr survived 25 years, and only 40% survived 20 years.