Primary stability of osteochondral grafts used in mosaicplasty

The goal of our experiments was to determine the primary stability of osteochondral grafts used in mosaicplasty. The effect of graft diameter and dilation, as well as multiple grafting, were studied in a porcine model.

Single osteochondral grafts, 4.5 and 6.5 mm in diameter, and multiple grafts were transplanted from the trochlea of porcine femurs to the weight-bearing area of the lateral femoral condyle. In the multiple grafting series, 3 grafts 4.5 mm in diameter were transplanted either in a row or in circular fashion. The grafts were first pushed in level with the surrounding cartilage surface, then they were pushed 3 mm below cartilage level. The push-in forces were measured. The effect of graft diameter and the extent of dilation on primary stability were studied as well as the influence of multiple grafting.

In the case of 4.5-mm grafts, the mean level push-in force was 43.5 N, and pushing 3 mm below cartilage level required a mean of 92.5 N (n = 13). In the case of 6.5-mm grafts, level push-in required a mean of 76.2 N, and for pushing 3 mm below cartilage level a mean of 122.2 N force had to be used (n = 14). The length of the drill hole and the dilation were both 20 mm in each setting. When using 20-mm long drill holes and 15-mm dilation length, the values above were found to be 36.6 N and 122.5 N in the case of 4.5-mm grafts (n = 12). Mean level push-in force in the first (row) multiple series was 31.8 N, and pushing 3 mm below cartilage level required a mean of 52.17 N (n = 7). In the second series (circle), level push-in required a mean of 30.44 N, and for pushing 3-mm below cartilage level a mean of 54.33 N force had to be used (n = 9). In the control series (1 single graft) the mean level push-in force was 38.7 N, and pushing 3 mm deeper required a mean of 86.8 N (n = 9).

These results suggest that grafts of greater diameter are more stable in absolute values and stability may be increased by shorter dilation length, whereas level push-in forces do not increase significantly. There is no difference in primary stability between grafts implanted in a row or in circular fashion, and multiple grafts may not be as stable as single grafts in the initial period after transplantation.

This is a randomized, controlled in vitro animal trial that helps us to better understand the primary stability of osteochondral grafts and to refine surgical techniques as well as postoperative protocols.