This study examined the rate of degeneration of the acetabular cartilage by the bipolar head according to time, and which clinical factors are related to the degeneration of the acetabular cartilage.

Among 192 patients (226 hip joint) who were received bipolar hemiarthroplasty from August 1996 to August 2002, 61 patients (65 hip joint), who were followed up for more than 2 years and showed no signs of dislocation, infection and functional problems, were enrolled in this study. A modified form of a computer assisted vector wear analysis program was used to measure the rate of degeneration of the acetabular cartilage. The subjects were divided into two groups, those whose amount of degeneration of the acetabular cartilage was less than average and those whose amount of degeneration was more than average. The factors that appeared to affect the level of acetabular degeneration in the two groups were evaluated.

After a bipolar hemiarthroplasty, the average linear degenerative change in the acetabular cartilage and the volumetric degenerative change was 0.23±0.107 mm/yr and 114±47.2 mm3/yr, respectively. The result showed significant differences with activity and the HHS between the two groups. The HHS showed a reverse relationship with the linear degeneration and volumetric degeneration, the activity showed a correlation with the linear and volumetric degeneration.

The acetabular cartilage degenerates faster as the patient's activity increases, and slower with a higher HHS. When surgeons perform hip joint arthroplasty, it is strongly recommended that the life expectancy and the level of activity be considered when deciding between a hemiarthroplasty or total hip arthroplasty.