To evaluate the clinical and histological results after microfracture surgery for degenerative arthritis of the knee.

Thirty-five patients, who had moderate to severe pain with no improvement after conservative treatment, moderate osteoarthritic change in standing AP radiogram, and no severe angular deformity, underwent microfracture surgery. Their mean age at the time of operation was 56 years (range, 33-75 years) and mean follow-up period was 1 year (range, 6-17 months) . In the 14 cases, 'second-look' arthroscopies and biopsies were performed at 6 months following microfracture for full thickness chondral lesions. At the last follow up clinical results were evaluated with Baumgaertner's scale. The specimens were stained with H-E, Safranin-O, and Masson's trichrome.

Most of the patients showed significant improvement clinically. 'Second-look' showed that the chondral defect areas were covered with newly grown grayish white tissues. Histologically, the regenerated tissue appears to be a hybrid of hyaline cartilage and fibrocartilage. There are viable chondrocytes in lacunae with a uniform matrix.

Microfracture surgery can induce chondral resurfacing for full thickness defects of osteoarthritic knee. However, the exact nature and fate of regenerated cartilagenous tissues need further long term follow-up study.