Tendon Properties Remain Altered in a Chronic Rat Rotator Cuff Model

Abstract

Background Chronic rotator cuff tears are often associated with pain or poor function. In a rat with only a detached supraspinatus tendon, the tendon heals spontaneously which is inconsistent with how tears are believed to heal in humans. Questions/purposes We therefore asked whether a combined supraspinatus and infraspinatus detachment in the rat would fail to heal and result in a chronic injury in the supraspinatus tendon. Methods We acutely detached the supraspinatus and infraspinatus tendons in a rat model. At 4, 8, and 16 weeks post-detachment, biomechanical testing, collagen organization, and histological grading were evaluated for the detached supraspinatus and infraspinatus tendons and compared to controls. Results In the detached supraspinatus tendon, area and percent relaxation were increased at all time points while the modulus and stiffness were similar to those of controls at 4 and 8 weeks. Collagen disorganization increased at late time points while cellularity increased and cells were more rounded in shape. In the detached infraspinatus tendon, area and percent relaxation were also increased at late time points. However, the modulus values initially decreased followed by an increase in both modulus and stiffness at 16 weeks compared to control. In the detached infraspinatus, we also observed a decrease in collagen organization at all time points and increased cellularity and a more rounded cell shape. Conclusions Due to the ongoing changes in mechanics, collagen organization and histology in the detached supraspinatus tendon compared to control animals at 16 weeks, this model may be useful for understanding the human chronic tendon tear. Clinical Relevance This rat rotator cuff chronic model can be used to test hypotheses regarding injury and repair mechanisms that cannot be addressed in human patients or in cadaveric studies.

Rat rotator cuff tendon-to-bone healing properties are adversely affected by hypercholesterolemia

“…Photomicrographs were blindly graded by 3 observers for assessment of cellularity and cell shape based on a scale of 0 (normal), 1 (mild changes), 2 (moderate changes), and 3 (marked changes), as done previously. 7 The same images were also analyzed for collagen organization with quantitative polarized light microscopy. With use of this technique, angular deviation (a measure of disorganization) was calculated for each specimen.…”

Comparison of rotator cuff muscle architecture among humans and selected vertebrate species

“…When making decisions about repair options, clinicians often refer to animal studies of rotator cuff injury that include mice (Thomopoulos et al, 2007), rats (Soslowsky et al, 1996), sheep (Gerber et al, 1999), rabbits (Björkenheim, 1989), dogs (Kujat, 1990), goats and others (Adams et al, 2006;Das et al, 2011;Grumet et al, 2009;MacGillivray et al, 2006;Peltz et al, 2009;Uggen et al, 2010). Although a variety of animal models have been used to study rotator cuff disease, questions remain about their relevance to humans, because of differences in their basic muscle architecture, bony anatomy and healing capacity (Brand, 2008;Dourte et al, 2010;Soslowsky et al, 1996).…”

The Effect of Granulocyte-colony Stimulating Factor on Rotator Cuff Healing After Injury and Repair

“…Furthermore, we found that tendon cross-sectional area remained constant in the G-CSFtreated group between 12 and 19 days, whereas the control group exhibited a decrease in cross-sectional area. Dourte et al have previously shown that normally healing tendons demonstrate a steady decrease in cross-sectional area during remodeling [9]. The lack of significant increases in mechanical properties and decreases in tendon cross-sectional areas may represent delayed healing.…”