PROGRESSION OF RADIOLUCENT LINES ADJACENT TO THE ACETABULAR COMPONENTAND FACTORS INFLUENCING MIGRATION AFTER CHARNLEY LOW-FRICTION TOTAL HIP-ARTHROPLASTY

We analyzed the progression of radiolucent lines around the acetabular cup after 452 Charnley low-friction arthroplasties that had been perf ormed in 392 patients between 1971 and 1976. The average duration of f ollow-up was twenty years (range, eleven to twenty-five years) for the 442 hips (382 patients) that had the original component in place at t en years. The demarcation of the bone-cement interface was classified according to the system of Hodgkinson et al. We sought to determine if there was a relationship between the progression of the radiolucent l ine and the age, gender, and weight of the patient; the level of activ ity; the preoperative diagnosis; or the amount of wear of the acetabul ar cup. The demarcation increased over time in 138 (31 per cent) of th e 452 hips. Radiographs made at the time of the latest follow-up showe d migration of eleven (5 per cent) of the 233 acetabular cups with no demarcation on the initial postoperative radiograph, eighteen (11 per cent) of the 167 cups with type-1 demarcation, twelve (35 per cent) of the thirty-four cups with type-2 demarcation, and thirteen of the eig hteen cups with type-3 demarcation. Preoperative acetabular protrusion , inflammatory arthritis, and severe acetabular dysplasia as well as a previous operation were associated with the extent of the radiolucent line on the most recent radiograph (p < 0.05 for all). A high level o f activity and more than two millimeters of wear of the acetabular cup also were related to the progression of the radiolucent line (p = 0.0 004 and p < 0.0001, respectively). Kaplan-Meier survivorship analysis demonstrated that the greater the demarcation on the initial postopera tive radiograph, the greater the risk of migration (p < 0.0001, Mantel -Cox test). Our data suggest that, after a Charnley low-friction arthr oplasty, any cemented cup, even one with the least amount of demarcati on (types 0 and 1), can migrate. As the type of the initial postoperat ive demarcation increases, so does the risk of migration of the cup, p articularly when there is loss of the acetabular bone stock.