Rat supraspinatus muscle atrophy after tendon detachment

Abstract

Rotator cuff tears are one of the most common tendon disorders found in the healthy population. Tendon tears not only affect the biomechanical properties of the tendon, but can also lead to debilitation of the muscles attached to the damaged tendons. The changes that occur in the muscle after tendon detachment are not well understood. A rat rotator cuff model was utilized to determine the time course of changes that occur in the supraspinatus muscle after tendon detachment. It was hypothesized that the lack of load on the supraspinatus muscle would cause a significant decrease in muscle mass and a conversion of muscle fiber properties toward those of fast fiber types. Tendons were detached at the insertion on the humerus without repair. Muscle mass, morphology and fiber properties were measured at one, two, four, eight, and 16 weeks after detachment. Tendon detachment resulted in a rapid loss of muscle mass, an increase in the proportion of fast muscle fibers, and an increase in the fibrotic content of the muscle bed, concomitant with the appearance of adhesions of the tendon 10 surrounding surfaces. At 16 weeks post-detachment, muscle mass and the fiber properties in the deep muscle layers returned to normal levels. However, the fiber shifts observed in the superficial layers persisted throughout the experiment. These results suggest that load returned to the muscle via adhesions to surrounding surfaces, which may be sufficient to reverse changes in muscle mass.

Muscle Force and Power Following Tendon Repair at Altered Tendon Length

“…This finding argues against formation of new fibers with increased tension and removal of fibers with decreased tension, but supports re-establishing the baseline composition, and is consistent with prior studies [5,48]. Our resultant hypertrophied Type IIa and Type IIb fibers appear to run counter to the studies previously mentioned, where muscle demonstrates hypertrophy of slow fibers and a decrease in fast glycolytic fiber content when subjected to increased load [12,14,16,49].…”

“…Additionally, simply acutely dissecting extra-muscular connective tissue results in reduced muscle force output [47]. Subsequent to our experiment, it was shown that rat supraspinatus muscle, when simply tenotomized at its humeral insertion, returns to its pre-surgical mass and muscle size when allowed a 16 week recovery [48]. These findings support our "splinting" assertion.…”

Molecular mechanism of fatty degeneration in rotator cuff muscle with tendon rupture

“…6,24,25 The term ''infiltration'' conveys a sense of permeation of lipids into muscle. As we showed in this in vitro study, myoblasts can trans-differentiate to PPARg expressing adipocytes.…”

Sexual dimorphism of murine masticatory muscle function

“…Muscle preparations with more than 15% damage were eliminated from the study. Fiber area analysis was achieved using immunohistochemistry and an antibody recognizing laminin as previously described (13). The imaging software provided further confirmation that the fibers were no cut obliquely during sectioning.…”