RATE OF DEGENERATION OF HUMAN ACETABULAR CARTILAGE AFTER HEMIARTHROPLASTY

Biopsy specimens of cartilage and subchondral bone were obtained from the weight-bearing dome of the acetabulum in twelve elderly patients w ho were having a revision of a hemiarthroplasty of the hip because of pain. Biopsy specimens of acetabular cartilage and subchondral bone we re also obtained from eight patients of comparable age who were having a primary hemiarthroplasty for a displaced fracture of the femoral ne ck; these served as the control specimens. The specimens were stained with hematoxylin and eosin for the initial histological assessment of cartilage structure and cellularity as well as the integrity of the ti demark, Safranin-O and toluidine-blue stains were used to assess prote oglycan content. A histological grading scale was employed for compara tive analysis of samples. The joint space of the hip was measured on t he radiographs that were made before the revision and was correlated w ith the histological grade. Review of the histological specimens demon strated considerable degeneration of acetabular cartilage in the patie nts who were having a revision of a hemiarthroplasty as compared with that in the age-matched control patients who were having a primary hem iarthroplasty. The progression in the severity of the degeneration cor related directly with the duration of articulation of the implant with the acetabulum. All six of the patients in whom the implant had been in situ for more than five years, and in whom the femoral stem was det ermined to be stable at the operation, had nearly complete loss of car tilage as seen on histological examination, Similarly loss of radiogra phic joint space closely correlated with deterioration of the histolog ical grade of the acetabular cartilage. Acetabular cartilage degenerat es more rapidly in response to articulation with a metallic hemiarthro plasty component, The loss of radiographic joint space after the hemia rthroplasty predicted the histological degeneration of hyaline cartila ge in the acetabulum in all of the hips. Symptoms that are attributabl e to a hemiarthroplasty of the hip in a patient who has a femoral stem that is radiographically secure five years after implantation or more are probably due to abnormal wear of the acetabular cartilage.