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The purpose of this study was to evaluate the influence of hormonal milieu on endochondral growth. This was achieved by transplanting hind limbs of juvenile rats to syngeneic adult rats. Because there is no potential for rejection, the limb can be transplanted between animals of different ages, to study the influence of hormonal maturity on stimulation and cessation of physeal growth and maturation. Tibial length and the histologic appearance of the physis were recorded. Whole vascularized hind-limb transplantation in syngeneic Lewis rats was used. Group 1: Thirty-five transplants between animals of the same age (three weeks old) were performed (isochronografts). Group 2: In 35 procedures, the age of the donor was three weeks old and of the recipient, 15 weeks (heterochronografts). In the first two study groups, the transplanted limb was placed on the dorsal flank of the recipient animal without nerve reconstruction. Controls were the contralateral hind limb of the donor animal. Because the limb was transplanted with loss of femoral and sciatic nerve supply to the dorsal flank position, the effects of denervation and lack of weight bearing were also evaluated. Group 3: Thirty-five limbs in three-week-old animals were transposed to the dorsal flank position, after severing the femoral and sciatic nerves. Analysis of variance of tibial length was used to compare study groups. Limbs transplanted to older animals (heterochronografts--Group 2) achieved the greatest length, 91 percent of normal, and significantly more when compared to Groups 1 (84 percent) and 3 (83 percent) (p less than .005). Growth of the limb was adversely affected by limb position and denervation.(ABSTRACT TRUNCATED AT 250 WORDS)

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To study wound repair in rat Achilles tendon, we utilized a novel surgical method for immobilizing only one hind limb. In this technique, the femoral vessels were preserved while the skin, muscles, nerves and the shaft for the femur were transected. The limb was then rotated and sutured to lie on the posterolateral flank of the animal. The recovery was prompt and the procedure affected the routine growth and metabolism of the animal minimally throughout the period of experimentation. In the immobilized limb, healing of the Achilles tendon was studied after subtotal severance in the midsection. The rats were killed at intervals of 1, 2, and 4 weeks postoperatively. After 1 week, the surface of the wound was covered by a thin layer of cells. A gap persisted underneath and showed fibrovascular proliferation at the margins. In 2 weeks, the gap was completely occupied by fibrovascular tissue that was beginning to align along the long axis of the tendon. By the 4th week, remodeling had occurred and the site of the wound had almost blended with the rest of the tendon. We conclude that this new technique of hind limb immobilization causes little stress on the animal, and it can be useful for the study of tendon healing.