Skeletal extension development: criteria for future designs.

Experience with an intramedullary skeletal extension and a supracortical extension has been reviewed. Criteria for possible use in future developments have been outlined. Tissue interfacing with the material used in fabricating these devices were briefly discussed, stressing the importance of maintaining the skin's integrity. An artificial tendon, which attempts to bring the external mechanical ankle joint under the direct control of existing skeletal muscles, was described. Three animal models were reviewed and our reasons given for selecting the goat. Preoperative preparations, anesthesia, and the surgical procedures were described in some detail. A tabulation of the procedures done on 52 goats (Table 1) shows little difference between the intramedullary rod and the supracortical devices when only the times in place are compared. However, the supracortical devices showed no bone necrosis and produced only one case of osteomyelitis. With the intramedullary rod, five cases of necrosis and/or osteomyelitis were seen. The cone-shaped supracortical devices are somewhat vulnerable to forces in extension.