Effect of tibial lengthening on the gastrocnemius muscle. A histopathologic and morphometric study in rabbits.

We observed the changes of the gastrocnemius muscle in relation to the percentage of lengthening of the rabbit's tibia by callotasis. 75 rabbits were separated into 3 lengthening groups, 10, 20, and 30 percent lengthening, respectively. Histopathologic observations, based on the fiber size variation, internalization of the nuclei, degeneration, regeneration, and endomysial fibrosis of muscle fibers, revealed that substantial changes occurred in the latter groups. Histomorphometrically, the decrease in the mean size of Types I and II muscle fibers was observed in all lengthening groups, but there was no significant change in the proportion of the muscle fiber types in any of the lengthening groups.