Split-line pattern and histologic analysis of a human osteochondral plug graft.

The split-line pattern of collagen fibers in articular cartilage is oriented according to weight-bearing stresses. The importance of aligning the split-line pattern of articular cartilage in human osteochondral plug grafts relative to the surrounding cartilage has been proposed but not evaluated clinically. The purpose of this case report is to compare the articular split-line pattern with the histologic analysis of a specimen obtained from a patient who underwent an osteochondral plug transfer procedure with subsequent conversion to joint arthroplasty. The fresh osteochondral section obtained at total knee arthroplasty, including the area treated 18 months earlier with an osteochondral plug transfer, was fixed in formalin. Split-lines were demonstrated on the surface using a needle dipped in India ink. After decalcification and paraffin embedding, the specimen was sectioned and stained with Safranin O and fast green for histologic analysis. The split-line pattern of the anterior portion of the graft was oriented parallel to the resident cartilage; however, collagen orientation was divergent (approximately 30 degrees oblique) to the surrounding cartilage near the posterior portion of the graft. It was at this margin that further resident articular degeneration was noted despite the plug articular surface remaining relatively intact. Although bony incorporation of the plug occurred, there was a residual chondral cleft at the graft-host interface. Our report suggests that an osteochondral plug transfer can survive despite a slightly divergent collagen split-line pattern of plug relative to the resident articular bed. Perhaps more important to the clinical outcome is the selection of true focal, traumatic lesions rather than lesions degenerative in etiology, no matter how focal they appear.