Recovery of muscle transfers replacing the total plantar flexor muscle group in rats

In rats,combinations of plantar flexor muscles representing ~20, 40, 60, and80% of the mass of the total plantar flexor group were transferredorthotopically in the absence of synergistic muscles and allowed torecover for 120 days. We hypothesized that, compared with theirindividual control values for structural and functional variables, thetransfers would display a hierarchical array of deficits, proportionalto their initial mass and, consequently, inversely proportional to therelative load on the transfers. Surprisingly, compared with theirindividual control values, each muscle transfer displayed deficits of30-40% in muscle mass, total fiber cross-sectional area, andmaximum isometric force, with the exception of the smallest transfer,the plantaris (PLN) muscle, which recovered 100% of its control valuefor each of these variables. Therefore, except for the PLN transfer,the muscle transfers studied displayed deficits similar in magnitude tothose reported for muscles transferred in the presence of synergisticmuscles. The greater recovery of the PLN transfer was attributed to therelatively large requirement for force production imposed on thistransfer due to the average force requirements of the total plantarflexor group.