To evaluate the clinical and radiologic results, second-look arthroscopic findings, histologic evaluation, and results of immunohistochemical staining and the Western blotting test for type II collagen after microfracture for full-thickness chondral defects in patients with osteoarthritic knee.

Between October 1997 and December 1998, 49 knees in 46 patients who had moderate osteoarthritic changes underwent microfracture; 44 patients (47 cases) had second-look arthroscopy and biopsy performed 1 year after surgery. The clinical outcomes were assessed by use of Baumgaertner’s 9-point scale and joint space changes were measured radiographically; 18 knees underwent immunohistochemical study and 21 knees underwent Western blotting tests to identify formation of type II collagen.

Significant improvements were noted for the parameters of daily living activity and pain (P < .05). The joint spaces were widened by 1.06 mm on standing anteroposterior and by 1.37 mm on standing lateral radiographs, which showed statistical significance (P < .05). Individual defects were filled with white tissue resembling cartilage on second-look arthroscopy, and the cartilage healing was found by histologic evaluation. Type II collagen formation was identified qualitatively by immunohistochemical staining. Quantitative collagen formation by Western blotting showed 44% growth compared with the normal control. This healed tissue is a combination, or hybrid, of fibrocartilage and hyaline-like cartilage, and it is shown to contain type II collagen on immunohistochemical staining and the Western blotting test.

Patients with full-thickness chondral defects in the osteoarthritic knee can have improved function and see an increase in joint space after microfracture. Cartilaginous tissue containing type II collagen is formed after the microfracture procedure in the osteoarthritic knee.

Level IV, retrospective case series.