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 who were having a revision of a hemiarthroplasty of the hip because of pain. Biopsy specimens of acetabular cartilage and subchondral bone were also obtained from eight patients of comparable age who were having a primary hemiarthroplasty for a displaced fracture of the femoral neck; 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 tidemark, Safranin-O and toluidine-blue stains were used to assess proteoglycan content. A histological grading scale was employed for comparative analysis of samples. The joint space of the hip was measured on the radiographs that were made before the revision and was correlated with the histological grade. Review of the histological specimens demonstrated considerable degeneration of acetabular cartilage in the patients who were having a revision of a hemiarthroplasty as compared with that in the age-matched control patients who were having a primary hemiarthroplasty. The progression in the severity of the degeneration correlated 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 determined to be stable at the operation, had nearly complete loss of cartilage as seen on histological examination, Similarly loss of radiographic joint space closely correlated with deterioration of the histological grade of the acetabular cartilage. Acetabular cartilage degenerates more rapidly in response to articulation with a metallic hemiarthroplasty component, The loss of radiographic joint space after the hemiarthroplasty predicted the histological degeneration of hyaline cartilage in the acetabulum in all of the hips. Symptoms that are attributable 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.