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Open Access Methodology article

Device for lengthening of a musculotendinous unit by direct continuous traction in the sheep

Matthias A Zumstein13, Eric Frey1, Brigitte von Rechenberg45*, Robert Frigg2, Christian Gerber15 and Dominik C Meyer15

Author Affiliations

1 Dept. of Orthopedics, University of Zurich, Balgrist, Zürich, 8008, Switzerland

2 Chief Technology Officer, Synthes GmbH, Muracherstrasse 3, 2544, Bettlach, Switzerland

3 Dept of Orthopedics, University of Berne, Inselspital, Bern, 3010, Switzerland

4 Musculoskeletal Research Unit (MSRU), Equine Hospital, Vetsuisse Faculty, University of Zurich, Winterthurerstrasse 260, 8057, Zurich, Switzerland

5 Competence Center for Applied Biotechnology and Molecular Medicine (CABMM), Vetsuisse Faculty, University of Zurich, Winterthurerstrasse 190, 8057, Zürich, Switzerland

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BMC Veterinary Research 2012, 8:50  doi:10.1186/1746-6148-8-50

Published: 2 May 2012



Retraction, atrophy and fatty infiltration are signs subsequent to chronic rotator cuff tendon tears. They are associated with an increased pennation angle and a shortening of the muscle fibers in series. These deleterious changes of the muscular architecture are not reversible with current repair techniques and are the main factors for failed rotator cuff tendon repair. Whereas fast stretching of the retracted musculotendinous unit results in proliferation of non-contractile fibrous tissue, slow stretching may lead to muscle regeneration in terms of sarcomerogenesis. To slowly stretch the retracted musculotendinous unit in a sheep model, two here described tensioning devices have been developed and mounted on the scapular spine of the sheep using an expandable threaded rod, which has been interposed between the retracted tendon end and the original insertion site at the humeral head. Traction is transmitted in line with the musculotendinous unit by sutures knotted on the expandable threaded rod. The threaded rod of the tensioner is driven within the body through a rotating axis, which enters the body on the opposite side. The tendon end, which was previously released (16 weeks prior) from its insertion site with a bone chip, was elongated with a velocity of 1 mm/day.


After several steps of technical improvements, the tensioner proved to be capable of actively stretching the retracted and degenerated muscle back to the original length and to withstand the external forces acting on it.


This technical report describes the experimental technique for continuous elongation of the musculotendinous unit and reversion of the length of chronically shortened muscle.

Muscle; Sheep; Retraction; Fatty infiltration; Atrophy; Pennation angle; Continuous traction