Tendon retracts more than muscle in experimental chronic tears of the rotator cuff.
We released the infraspinatus tendons of six sheep, allowed retraction of the musculotendinous unit over a period of 40 weeks and then performed a repair. We studied retraction of the musculotendinous unit 35 weeks later using CT, MRI and macroscopic dissection. The tendon was retracted by a mean of 4.7 cm (3.8 to 5.1) 40 weeks after release and remained at a mean of 4.2 cm (3.3 to 4.7) 35 weeks after the repair. Retraction of the muscle was only a mean of 2.7 cm (2.0 to 3.3) and 1.7 cm (1.1 to 2.2) respectively at these two points. Thus, the musculotendinous junction had shifted distally by a mean of 2.5 cm (2.0 to 2.8) relative to the tendon. Sheep muscle showed an ability to compensate for approximately 60% of the tendon retraction in a hitherto unknown fashion. Such retraction may not be a quantitatively reliable indicator of retraction of the muscle and may overestimate the need for elongation of the musculotendinous unit during repair.
Meyer
D C
DC
Department of Orthopaedics, University of Zurich, Switzerland.
Lajtai
G
G
von Rechenberg
B
B
Pfirrmann
C W A
CW
Gerber
C
C
D000818:Animals; D001696:Biomechanical Phenomena; D005260:Female; D008279:Magnetic Resonance Imaging / Q000379:methods; D018485:Muscle Fibers, Skeletal / Q000473:pathology; D010027:Osteotomy / Q000379:methods; D017006:Rotator Cuff / Q000473:pathology / Q000601:surgery; D000070636:Rotator Cuff Injuries; D012421:Rupture / Q000601:surgery; D012756:Sheep; D013708:Tendon Injuries / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery; D013997:Time Factors; D014057:Tomography, X-Ray Computed / Q000379:methods