Study on Deformity Induced by Partial Excision of Distal Femoral Epiphyseal Plate in Rats

Chang, J S; Lee, D Y; Chung, M S

Abstract

Injuries to the physis of a growing bone result in either angular deformity or shortening, depending on partial or total growth arrest. It is commonly believed that defect or loss of the physis and epiphysis results in similar growth disturbance. Age at the time of injury also affects the final outecome of the growth disturbance. Precise relationship between the age of injury and deformities at the end of growth has not been elaborated however. It is generally understood that the younger the more severe the deformities due to growth potential, while, on the other hand, the younger the more active the remodeling capacity. How these two seemingly contradicting phenomena interact in the growth of an jnjured bone remains largely speculative. In order to observe the effect of age upon deformities at the end of growth due to injury to the physis, we resected the medial one third of the medial femoral condyle including the physis and the epiphysis of the femur in seventy four rats at one, three, five, seven, nine weeks of age. In the corresponding groups ninty rats were subjected to soft tissue dissection alone. At fifteen weeks of age, by which time growth was complete, the animals were sacrificed and both hind-limbs were dissected free of soft tissue. The varus angle and the length of the femur on both the operated and normal sides were measured in the experimental and control groups. Following results were obtained 1. The varus angle was significantly increased in all the age groups in the experimental group, while there was no significant change in the control group. Varus deformity was most pronounced in the three-week group with 51.2+/âˆ’17.7 degrees, and next was one week group with 27.8+/âˆ’ 10.4 degrees, but there was no statistical difference amongst the rest of the group(p<0.05). 2. The femoral length was significantly shortened in all the groups in the expermental group, while there was no significant change in the control group. Shortening was more pronounced in the one- and three-week groups with 0.46 +/âˆ’0.20 cm and 0.55 +/âˆ’0.32 cm, respectively, but there was no significant difference between the two(p<0.05). It is concluded that following jnjury to the physis of the medial condyle of the femur in rats, significant varus deformity and shortening were observed at the end of growth(p<0.05). An interesting observation was the fact that growth disturbance in the one-week group was less severe than in the three-week group. This may suggest that remodeling capacity is very active during the very early infancy.