Progression of radiolucent lines adjacent to the acetabular component and 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 performed in 392 patients between 1971 and 1976. The average duration of follow-up was twenty years (range, eleven to twenty-five years) for the 442 hips (382 patients) that had the original component in place at ten 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 line and the age, gender, and weight of the patient; the level of activity; the preoperative diagnosis; or the amount of wear of the acetabular cup. The demarcation increased over time in 138 (31 per cent) of the 452 hips. Radiographs made at the time of the latest follow-up showed 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 eighteen 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 of activity and more than two millimeters of wear of the acetabular cup also were related to the progression of the radiolucent line (p = 0.0004 and p < 0.0001, respectively). Kaplan-Meier survivorship analysis demonstrated that the greater the demarcation on the initial postoperative radiograph, the greater the risk of migration (p < 0.0001, Mantel-Cox test). Our data suggest that, after a Charnley low-friction arthroplasty, any cemented cup, even one with the least amount of demarcation (types 0 and 1), can migrate. As the type of the initial postoperative demarcation increases, so does the risk of migration of the cup, particularly when there is loss of the acetabular bone stock.