Tendon retracts more than muscle in experimental chronic tears of the rotator cuff

Abstract

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 The tendon was retracted by a mean of 4.7 cm (3.8 to 5.1) 40 weeks after release and remained at a mean of 4.2 cm (3.3 to 4.7) 35 weeks after the repair.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.

Preclinical Models for Translating Regenerative Medicine Therapies for Rotator Cuff Repair

“…Rotator cuff injury and repair has been investigated in large animal models, including rabbit, [52][53][54][55][56][57][58][59][60] goat, 61,62 sheep, [63][64][65][66][67][68] and dog. [69][70][71][72][73][74][75][76] (Although the rabbit may be considered by some to be a small animal, it is grouped with the large animals because it is in many ways more similar to the large animals than to the rat with respect to the points of this discussion.)…”

Anabolic Steroids Reduce Muscle Damage Caused by Rotator Cuff Tendon Release in an Experimental Study in Rabbits

“…So far, investigators have failed to quantitatively satisfactorily reproduce the characteristic muscular changes seen in humans and sheep with use of the rat model 34,35 . The sheep model is well established for investigations of muscular and tendinous rotator cuff abnormality 5,10,[36][37][38][39] . Although investigations in which technical feasibility (e.g., implantation of a device to continuously relengthen retracted myotendinous units 10 ) favors largeanimal models, we found the current smaller-animal model suitable to answer the research questions at hand while reducing the cost and ethical burden.…”

Tendon Collagen Crosslinking Offers Potential to Improve Suture Pullout in Rotator Cuff Repair: An Ex Vivo Sheep Study

“…First, we used healthy sheep tendons and therefore did not consider how compromised tendon tissue quality associated with tears could affect the outcome. However, the sheep infraspinatus tendon is a well-established model for investigations of rotator cuff tendon tears [4,11,19,25,32]. It also is possible and likely that the use of degenerated tendons might reveal a larger effect of genipin differences owing to increased tissue permeability and related functional effects of the applied crosslinking [16].…”

“…Massive tears usually are chronic and associated with myotendinous retraction [25], loss of musculotendinous elasticity [22], muscle atrophy, and fatty infiltration of the muscle [21]. If a massive rotator cuff tear can be repaired, short-and long-term clinical results are excellent and joint degeneration can be markedly decelerated or even arrested [1,6,10,18].…”