Progressive cancellous and cortical bone remodeling after press-fit cup fixation

Periprosthetic bone loss after total hip arthroplasty is common. It can be progressive and, in the extreme, may compromise survival of the prosthesis. With quantitative computed tomography, we determined the pattern of periacetabular cortical and cancellous bone density changes after press-fit cup implantation with alumina liners. We recruited 24 patients (24 hips; 15 men and nine women) with degenerative joint disease and used a press-fit cup with an alumina/alumina pairing. The average patient age was 57 years. Computed tomography examinations were performed 10 days, I year, and 3 years after the index operation. Cancellous bone density decreased in all periacetabular regions by as much as -66%; the decrease was progressive between the 1- and 3-year examinations. In contrast, cortical bone density above the dome of the cup remained constant but progressively decreased by as much as -22% at the level of the cup 3 years postoperatively. Within the first 3 postoperative years, progressive periacetabular remodeling of cancellous and cortical bone structures was observed after press-fit cup fixation. The bone density changes suggest high stress shielding of retroacetabular cancellous bone while load is transmitted solely to the cortical bone above the dome of the cup.