ABSTRACT
BACKGROUND: Although clinical investigations indicate that the limit of reversibility of rotator cuff muscles fibers type I and II atrophy is grade 2 of fatty degeneration (FD) according to the Goutallier computed tomography classification, little is known about the morphometric verification of these findings. METHODS: The supraspinatus tendon was detached from the greater tubercle and the infraspinatus and subscapularis in 12 rabbits, and a 12-week observation period followed. This proved to be sufficient for development of grade >2 FD of the supraspinatus tendon. The tendon was then reinserted. The animals were euthanized 24 weeks after tendon reconstruction. The sections of middle part of supraspinatus were stained for adenosine triphosphatase reaction, and morphometric measurements were taken of type I and II muscle fiber diameters. The contralateral shoulders served as controls. RESULTS: The macroscopic inspection of the supraspinatus tendons revealed complete healing in all cases. No statistically significant differences were found between controls and operated-on shoulders for type I (P = .13) and type II (P = .55) muscle fibers. CONCLUSIONS: Atrophy of type I and II muscle fibers in rabbit supraspinatus muscle, characterized by grade >2 fatty degeneration according to the Goutallier computed tomography classification, is reversible after 24 weeks from reattachment of its tendon. A requirement for type I and II muscle fibers hypertrophy is a change in the biomechanical and functional conditions of the muscle after its tendon is reconstructed.
