Small cartilage defects treated with microfracture show comparable clinical results to those treated with ACI (autologous chondrocyte implantation). Unfortunately, the regenerative tissue generated by microfracture treatment does not exhibit the structure and function of hyaline articular cartilage. Adult mesenchymal stem cells are supposed to be capable of differentiating according to mechanical stimuli, e.g. into chondrocytes, thus generating hyaline cartilage. The treatments used so far, such as the microfracture procedure, are only able to induce mechanically insufficient fibrocartilage. The purpose of the present study was to test the influence of a resorbable implant manufactured from PGLA (polyglycollic-co-lactic acid) fleece in combination with microfracture in the weight-bearing area of the femoral condyle of mature sheep on cartilage repair. Artificial chondral defects (diameter: 8 mm) were created and treated with microfracture, with a PGLA implant alone or with a combination of both (n=6 for each group). Untreated empty defects served as controls. Under thorough pain control, full weight bearing was permitted immediately after the operation. After 12 weeks, the animals were killed and the operated knees were removed and histologically processed. First, the degree of covering of the defect with regenerative tissue was measured; then, the quality of the regenerate was evaluated using the score of O'Driscoll, Keeley and Salter [(1986) J. Bone Joint Surg. Am. 68, 1017-1035], which was modified to include histochemical labelling results. The combination of PGLA implant and microfracture led to a significant improvement of the quality of the regenerate when compared with microfracturing alone.

Different approaches exist for the treatment of small articular cartilage defects. Several studies show comparable results for autologous chondrocyte implantation (ACI) and microfracture. Unfortunately, the fibrocartilage resulting from microfracture has neither the structure nor the mechanical properties of hyaline cartilage, even though the adult mesenchymal stem cells, which immigrate into the defect, are supposed to differentiate into chondrocytes. This study was performed to examine the capacity of a resorbable implant made from polylactide-co-glycolide acid (PGLA)-fleece combined with autologous bone marrow cells fixed with a fibrin/thrombin-clot in the weight-bearing area of the femoral condyle of mature sheep. For this study, six defects were treated with either the PGLA-implant alone or with a combination of the implant with added fibrin glue or were left untreated to serve as controls. The animals were sacrificed after 12 weeks; the operated knees were removed and examined by measuring the covering of the defect with cartilaginous tissue and according to the score of O'Driscoll. Additional criteria such as immunolabeling for collagen II and aggrecan were included. Results showed that no improvement of the tissue quantity or quality could be achieved by increasing the cell load of the implant with cells fixed by fibrin glue.