Thigh muscle atrophy after femoral shortening. Vastus intermedius cross-section studied in osteotomized rats.

We determined the effect of a shortening/lengthening osteotomy on muscle fiber cross-sectional area in the vastus intermedius in 14 rats. The left femur was shortened 5 mm in half of the rats and elongated 5 mm in the other half. In both groups, the right femur was osteotomized and stabilized without shortening/lengthening. After 3 months, open biopsy specimens of the vastus intermedius were taken for measurements of the muscle cross-sectional area in both Type 1 and Type 2 fibers; 150 fibers were measured in each specimen. In the shortened group, the cross-section was reduced in both types of fibers. After lengthening, no differences in the fiber cross-sectional area were found. We conclude that differences in stretch and tension of the muscles are responsible for the atrophy after femoral shortening and the maintenance of the fiber cross-sectional area after lengthening.