Osteochondral repair of primate knee femoral and patellar articular surfaces: implications for preventing post-traumatic osteoarthritis

Abstract

The risk of post-traumatic osteoarthritis following an intra-articular fracture is determined to large extent by the success or failure of osteochondral repair. To measure the efficacy of osteochondral repair in a primate and determine if osteochondral repair differs in the patella (PA) and the medial femoral condyle (FC) and if passive motion treatment affects osteochondral repair, we created 3.2 mm diameter 4.0 mm deep osteochondral defects of the articular surfaces of the PA and FC in both knees of twelve skeletally mature cynomolgus monkeys. Defects were treated with intermittent passive motion (IPM) or cast-immobilization (CI) for two weeks, followed by six weeks of ad libitum cage activity. We measured restoration of the articular surface, and the volume, composition, type II collagen concentration and in situ material properties of the repair tissue. The osteochondral repair response restored a mean of 56% of the FC and 34% of the PA articular surfaces and filled a mean of 68% of the chondral and 92% of the osseous defect volumes respectively. FC defect repair produced higher concentrations of hyaline cartilage (FC 83% vs. PA 52% in chondral defects and FC 26% vs. PA 14% in osseous defects) and type II collagen (FC 84% vs. PA 71% in chondral defects and FC 37% vs. PA 9% in osseous defects) than PA repair. IPM did not increase the volume of chondral or osseous repair tissue in PA or FC defects. In both PA and FC defects, IPM stimulated slightly greater expression of type II collagen in chondral repair tissue (IPM 81% vs. CI 74%); and, produced a higher concentration of hyaline repair tissue (IPM 62% vs. CI 42%), but IPM produced poorer restoration of PA articular surfaces (IPM 23% vs. CI 45%). Normal articular cartilage was stiffer, and had a larger Poisson's ratio and less permeability than repair cartilage. Overall Cl treated repair tissue was stiffer and less permeable than IPM treated repair tissue. The stiffness, Poisson's ratio and permeability of femoral condyle cast immobilized (FC CI) treated repair tissue most closely approached the normal values. The differences in osteochondral repair between FC and PA articular surfaces suggest that the mechanical environment strongly influences the quality of articular surface repair. Decreasing the risk of post-traumatic osteoarthritis following intra-articular fractures will depend on finding methods of promoting the osteochondral repair response including modifying the intra-articular biological and mechanical environments.

Top. The poorest repair of a femoral condylar defect.

Middle

Moderate chondral repair tissue.

Bottom

The specimen with the most complete repair of the defect. The outlines of the defect are difficult to identify.

Top

The poorest repair of a patellar defect.

Middle

Some chondral repair tissue is visible.

Bottom

The specimen with the most complete repair of the defect.

Figure 3. Articular Surface Restoration

Histogram showing that the osteochondral repair response restored more of the articular surface in femoral defects than in patellar defects and that patellar defects treated by cast immobilization had better restoration of the articular surface than patellar defects treated by IPM.

Top

The osseous portion of the defect is filled with new bone and chondral repair tissue projects above the normal articular surface.

Bottom

The osseous portion of the defect contains fibrovascular tissue as well as bone and the chondral portion of the defect contains primarily fibrous tissue.

Figure 5. Volume of Repair Tissue

Histogram showing that repair tissue filled more than 90% of the osseous defect volume but only about 68% of the chondral defect volume.

Figure 6

Photomicrograph showing chondral repair tissue with a hyaline appearance.

Figure 7. Material Properties of Repair Tissue

Histogram showing that the osteochondral repair response produced tissue that most closely approached the properties of a normal articular surface in femoral condylar defects treated by cast immobilization.