Resurfacing hip arthroplasty. Classification of loosening and the role of prosthesis wear particles.

Operative grading of loosening and histologic examination of the periprosthetic tissues and the femoral and acetabular bone-cement interfaces were undertaken in 72 revised resurfacing hip arthroplasties. By correlating the degree of macroscopic and microscopic loosening at the bone-cement interface, a classification of the stages of loosening at the bone-cement interface was devised. Examination of the femoral bone-cement interface of solidly fixed prosthesis components has demonstrated the presence of polyethylene wear particles and a macrophage response at the interface prior to loosening. This suggests that wear particles may migrate along bone-cement interfaces that are both macroscopically and microscopically solid, and emphasizes the important role of wear particles in prosthesis loosening.