Asymmetric atrophy of the supraspinatus muscle following tendon tear

Abstract

Muscle atrophy is a known consequence of muscle disuse, muscle denervation and tendon tear. Whereas after nerve injury muscle atrophies in the denervated area, the distribution of muscle atrophy following tear of its tendon is not known.Standardized MRI scans of 64 consecutive, painful shoulders were evaluated for supraspinatus tendon tearing, myotendinous retraction, supraspinatus muscle atrophy, fatty infiltration, ratio of the scapular (deep) and fascial (superficial) muscle area ("symmetry'') and position of the central tendon within the supraspinatus fossa.There were thirteen shoulders with no and eleven shoulders with partial thickness supraspinatus tendon tears. In the forty cases with full thickness tendon tear, there was significant muscle atrophy and fatty infiltration. Atrophy of the fascial muscle portion was 43%, on the bony side it was 9% ( p < 0.005). The position of the central tendon within the supraspinatus fossa, was unaltered.Muscular changes following tendon tear occur highly asymmetrically: The muscle portion originating from the fascia primarily atrophies, the portion originating from the scapula primarily undergoes fatty infiltration. Muscular changes are not simply a consequence of muscle disuse, but dependent on architectural changes in the muscle.

Classifications in Brief: Goutallier Classification of Fatty Infiltration of the Rotator Cuff Musculature

“…The physical cross-section of the examined muscle also may differ substantially depending on how far a torn tendon has retracted. Meyer et al [25] showed, on MRI studies, that the superficial portion of the supraspinatus tendon reacts differently to tendon retraction than the deep portion, suggesting architectural changes in muscle belly fibers. These findings were confirmed in an experimental sheep model in which retracted tears had a greater amount of fatty infiltration [9].…”

Variation in external rotation moment arms among subregions of supraspinatus, infraspinatus, and teres minor muscles

“…Rotator cuff tear causes morphologic changes to the cuff's muscles and tendons [1][2][3][4] that can alter the mechanical performance of the joint by decreasing joint stability. [5][6][7] Additionally, shoulder rotation strength is known to decrease following rotator cuff tears.…”

Adipogenic and myogenic gene expression in rotator cuff muscle of the sheep after tendon tear

“…1,2 Fatty infiltration, muscle atrophy, and increase of interstitial connective tissue results in impaired physiological functions of tenotomized skeletal muscles. [3][4][5][6][7] Whereas rotator cuff with muscular atrophy may partly recover, 1,8 fatty infiltration of the rotator cuff muscles appears to be irreversible in the human shoulder. 1,2 Understanding the molecular pathomechanisms of these muscular changes would greatly help, first, to understand the disease process, and second, to design new treatment strategies to prevent its initiation.…”