Functional Evaluation at the Medial Gastrocnemius Donor Site in Rats

The transfer of a skeletal muscle from a donor to a recipient site creates an initial deficit in the structure and function of the muscle group from which it originates. Removal of the donor muscle induces hypertrophy of the remaining synergistic muscles, which compensate for part of the deficit at the donor site. The medial gastrocnemius (MGN) muscle is a frequently utilized donor muscle. Compared with the mass and force production of the control four-muscle plantar flexor group in rats, removal of the MGN muscle creates an initial deficit of 36 percent. At 60, 90, and 120 days after removal of the MGN muscle, the degree of compensation of the remaining three-muscle plantar flexor group (lateral gastrocnemius, soleus, and plantaris muscles) was evaluated. The mass of the three-muscle group increased 13 percent over the time course studied, but was still 28 percent less than the mass of the control four-muscle group. Similarly, the maximum force of the three-muscle group increased 27 percent, but was 21 percent lower than the control four-muscle group. The authors propose a model that illustrates the function restored at a donor site in terms of the percentage of the total muscle group comprised by the donor muscle and the ability of the remaining muscle group to compensate for its removal.