THE QUALIFICATION OF DIFFERENT FREE MUSCLE TRANSPLANTS TO RECONSTRUCTMIMIC FUNCTION - AN EXPERIMENTAL-STUDY IN RABBITS

With the scutuloauricularis muscle, we developed a new model for exper imental free transplantation of mimic muscles in the rabbit and studie d the qualification of different muscles for free functional grafting into the position of the facial muscle, which is to be replaced. Forty adult female white New Zealand rabbits were distributed to four group s of 10 rabbits each. In group 1, the operative techniques of the new transplantation models were developed in the scutuloauricularis muscle , the pectoralis descendens muscle, and a comparable part of the rectu s femoris muscle. In group 2, the scutuloauricularis muscle was transp lanted orthotopically with microneurovascular anastomoses on the left side; in group 3, the pectoralis descendens muscle was transplanted in to the position of the scutuloauricularis after its removal; and with the animals in group 4, a piece of the rectus femoris muscle was trans planted into the position of the mimic muscle after its removal. In al l muscle transplants, the neurovascular supply was reestablished micro surgically by end-to-end anastomoses to the superficial temporal vesse ls and direct nerve coaptation to the facial nerve branches supplying originally the scutuloauricularis muscle. Nine months after transplant ation, force measurements were performed in all transplanted muscles a nd the scutuloauricularis muscles of the control side. Cross-sections stained for ATPase after alkaline preincubation at pH 10.4 were used f or computer-assisted planimetry of the muscle fibers.The orthotopicall y transplanted scutuloauricularis muscles reached with 2.84 (+/- 1.04) N for maximal tetanic tension on the average 87.7 (+/- 32.1) percent of that of the control scutuloauricularis muscles, the pectoralis desc endens muscles with 4.25 (+/- 2.15) N on the average 188.7 (+/- 100.7) percent of that of the controls, and the pieces of rectus femoris mus cles 6.62 (+/- 2.16) N or 185.3 (+/- 45.4) percent of that of the cont rols. All three muscles were identified as fast contracting muscles be fore and after transplantation. By transplantation, the content of typ e II muscle fibers changed fr om 58.2 to 68.0 percent in the scutuloau ricularis muscle, from 62.4 to 74.4 percent in the musculus pectoralis descendens, and from 92.5 to 82.8 percent in the rectus femoris muscl e. For the first time, an experimental model for free transplantation of mimic muscles was developed and functionally assessed. The most imp ortant result of this study was the fact that the double-sized muscle grafts developed twice the force of the control scutuloauricularis mus cles, although reinnervated by the original muscle nerve branch. This result underlines the usefulness of overdimensioning during clinical m uscle transplantation. It was also shown that parts of big muscles can be grafted with results similar to those experienced with complete sm aller muscles.