252 THE JOURNAL OF BONE AND JOINT SURGERY THE EFFECT OF TENSION ACROSS A GROWING EPIPHYSIS

Stainless steel distraction springs were inserted across the upper tibial epiphyses often lambs and two calves. Evidence is submitted that tension increases epiphysial growth, but probably not sufficiently to be of clinical significance. It was suggested by Crilly (1972) and by Warrell and Taylor (1976) that reduction of pressure on the epiphysial cartilage might permit increase in growth. It had been recognised for some time that compression reduced epiphysial growth (Haas 1945) and Strobino, French and Colonna (1952) had examined the rate of bone growth under increasing compression. There is no record in the literature, however, of the effect of tension across a growing epiphysis. centimetre apart (Figs. 2 and 3). An identical procedure was carried out in the opposite limb with springs and markers, except that the springs were broken. The lambs were killed from four to twelve weeks later, and the distance between the bone markers measured on the post-mortem specimens. The springs were modified to produce parallel distraction equal to 1 0 kilograms weight by two springs inserted on the lateral and medial sides of bovine tibiae (Fig. 4). A larger animal was selected because insertion was technically more difficult. The upper tibial epiphysial plate was identified through lateral and medial incisions, the epiphysis drilled, and a hollow stainless steel rod inserted. A second rod was Table I. Effect of angular distraction across upper tibial epiphysis in ten lambs Lamb Age in weeks at Distance between distal end of markers at death (cm) Development of valgus deformity (degrees) ComplicationsOperation Death Control tibia Distracted tibi