The cartilage degeneration and joint motion of bipolar hemiarthroplasty.

PURPOSE: The outcomes of bipolar hemiarthoplasty for osteonecrosis of femoral head have been disappointing due to cartilage degeneration and osteolysis. We investigated the cartilage degeneration, joint motion, and factors associated with osteolysis.

METHODS

We retrospectively reviewed 134 bipolar hemiarthroplasties. The wear rate of acetabular cartilage was calculated. The ranges of motion of outer bearing and inner bearing were determined, and the ratio (O/I ratio) was calculated.

RESULTS

The mean degeneration rate of acetabular cartilage was 0.34 ± 0.35 mm/year. We could observe that the outer bearing motion was dominant, but decreased over time. In addition, the degeneration rate of cartilage and the decline rate of outer bearing motion of the osteolysis group were significantly higher than those of the control group.

CONCLUSIONS

Close observation is needed in cases of high degeneration rate of cartilage and rapid decline of outer bearing motion due to possibility of osteolysis.