Recombinant human bone morphogenetic protein-2 (rhBMP-2) (0, 0.1, 1, or 5 μg) was injected into the autogeneous semitendinosus tendon, and the tendon was transplanted to the region of the medial meniscus defect in a rabbit model to repair the defect. Cartilaginous transformation of the tendon by rhBMP-2 was expected under the less-vascularized intra-articular environment. At four and eight weeks after surgery, the left knee joints were harvested, and the morphological changes of the graft were examined by radiological, histological, and immunohistochemical methods. Cartilaginous tissue within the graft was detected by Safranin O staining and immunostaining of Type-II collagen. At four weeks, fibrocartilagenous tissue, together with small ossicles, was consistently noted in tendon autografts that were injected with 1 or 5 μg of rhBMP-2. At eight weeks, the cartilage located at the basal part of the graft adjacent to the joint capsule was partially replaced with ectopic bone in the 1-μg or 5-μg groups. The ossicles might have been formed by vascular invasion into the rhBMP-2-induced cartilage, but the cartilageous structure remained at the peripheral part of the graft and filled the meniscus defect. The experimental results indicate the potential use of rhBMP-2 in regenerating the cartilaginous meniscus if additional methods to suppress vascular invasion into the rhBMP-2–induced cartilage also inhibit ossification.
