Effects of function and weight-bearing on the healing of full-thickness cartilage defects in rats.

The effects of different degrees of active motion were studied in 30 male Wistar rats. In all rats a full-thickness cartilage defect of 1.0 mm in diameter was made in the medial condyle of both femurs. The rats were then allocated to the following three groups; i) exercising group which followed a 4-week training program of moderate intensity, ii) a non-weight-bearing group in which unilateral achilles tenotomy was made to reduce weight-bearing and iii) control rats which were allowed normal cage activity. Healing of the defect was evaluated by planimetric analysis and histologic evaluation. Effects of the training program was confirmed by a lesser weight increase in the exercise group. Planimetric analysis revealed no differences between the groups in the area of the original defect at the end of the experiment. There were no differences in healing ratio (area of healing/area of original defect) between the exercise and control groups, whereas the healing ratio was increased in the non-weight-bearing limbs compared with control and exercised rats. The favorable effect of non-weight-bearing was further indicated by differences in healing ratio between the two limbs in the non-weight-bearing group. Histological evaluation showed that the defect was repaired by a fibrocartilage substance along the periphery of the original defect and fibrovascular granulation tissue centrally. Evaluated by microscopic appearance, there were no qualitative differences between the three groups. We conclude that in the initial repair process by fibrocartilage non-weight-bearing is conductive to healing of full-thickness cartilage defects. The short-term effects revealed no differences on qualitative healing. Increased activity does not seem to prolong the initial fibrocartilage healing compared with normal activity with full weight-bearing.