~ ~~ zyxwvutsrqponmlkj Journal of Orthopaedic Research z www.elsevier.com/locate/orthres zy ELSEVIER Journal of Orthopaedic Research 23 (2005) 256258 Asymmetric atrophy of the supraspinatus muscle following tendon tear Dominik C. Meyer a, Christoph Pirkl a, Christian zyxw W.A. Pfirrmann b, Marco Zanetti ‘, Christian Gerber a zyxwvutsrqponmlkji Departtnent zyxwvutsrqpo of Orthopaedics. University of Zurich, Balgrist, Forchstrasse 340, 8008 Zurich, Switzerland Division of Radiology. Departmen t of Orthopaedics, University of Zurich. Balgrist. Forchstrasse 340, 8008 Zurich, Switzerland Received 15 March 2004; accepted 18 June 2004 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 (“sym- metry’’) 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% zyxwvuts (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 con- sequence of muscle disuse, but dependent on architectural changes in the muscle. zyxwv 0 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. Keyivords: Tendon rupture; Muscle degeneration; Fatty infiltration; Rotator cuff Introduction Following tear of its tendon, the musculotendinous unit retracts permanently, undergoes atrophy and fatty infiltration and looses elasticity [lo]. After few months, these changes appear to become irreversible [ 121 and are considered to be the main factor for persistent disa- bility particularly after rotator cuff tendon tears [9]. Cur- rently, fatty infiltration and atrophy of the rotator cuff muscles are both considered to be the consequence of disuse and degeneration [ 1,2,11,12,16] or denervation of the muscle [ 12-14]. The underlying pathophysiologic mechanisms leading to these changes, however, are poorly understood. On routine MR images of patients with rotator cuff tears, we have observed that not all parts of the supra- spinatus muscle undergo the same degree of atrophy and fatty infiltration suggesting that other factors than disuse must play a role. It was the purpose of this study to describe the precise macroscopic pattern of muscle atrophy and fatty infil- tration related to a supraspinatus tendon tear in man and to interpret the observed changes in the light of fu- Corresponding author. Tel.: +41 1 386 30 zyxwvuts 04; fax: +41 1 386 30 09. E-mail addresses: dominik.meyer@balgrist.ch (D.C. Meyer), chris- tian.pfirrmann@balgrist.ch (C.W.A. Pfirrmann), marco.zanetti@bal- grist:ch (M. Zanetti), christian.gerber@balgrist.ch (C. Gerber). ture attempts at treatment. 0736-0266/$ - see front matter 0 2004 Orthopaedic Research Society. Published by Elsevier Ltd. All rights reserved. doi: 10.101 6/j.orthres.2004.06.010