Supraspinatus tendon overuse results in degenerative changes to tendon insertion region and adjacent humeral cartilage in a rat model

Abstract

The etiology of rotator cuff tendon overuse injuries is still not well understood. Furthermore, how this overuse injury impacts other components of the glenohumeral joint, including nearby articular cartilage, is also unclear. Therefore, this study sought to better understand the time course of tendon protease activity in a rat model of supraspinatus overuse, as well as determine effects of 10 weeks of overuse on humeral head articular cartilage. For these studies, multiplex gelatin zymography was used to characterize protease activity profiles in tendon and cartilage, while histological scoring/mechanical testing and micro-computed tomography (μCT) imaging were used to quantify structural damage in the supraspinatus tendon insertion and humeral articular cartilage, respectively. Histological scoring of supraspinatus tendon insertions revealed tendinopathic cellular and collagen fiber changes after 10 weeks of overuse when compared to controls, while mechanical testing revealed no significant differences between tensile moduli (overuse: 24.5 ± 11.5 MPa; control: 16.3 ± 8.7 MPa). EPIC-μCT imaging on humeral articular cartilage demonstrated significant cartilage thinning (overuse: 119.6 ± 6.34 μm; control: 195.4 ± 13.4 μm), decreased proteoglycan content (overuse: 2.1 ± 0.18 cm−1; control: 1.65 ± 0.14 cm−1), and increased subchondral bone thickness (overuse: 216.2 ± 10.9 μm; control: 192 ± 17.8 μm) in the overuse animals. Zymography results showed no significant upregulation of cathepsins or matrix metalloproteinases in tendon or cartilage at 2 or 10 weeks of overuse compared to controls. These results have further elucidated timing of protease activity over 10 weeks and suggest that damage occurs to other tissues in addition to the supraspinatus tendon in this overuse injury model.

Full‐thickness rotator cuff tear in rat results in distinct temporal expression of multiple proteases in tendon, muscle, and cartilage

“…For muscle, we have previously shown significant fibrous tissue infiltration (indicative of muscle degeneration) 3 weeks following tendon injury . In our previous studies with tendon overuse injuries, we have observed concomitant humeral head cartilage damage by 12 weeks after tendon injury onset.…”

“…In particular, prior work has identified a positive correlation between amount of cathepsin K present and osteoarthritis severity in mice and cathepsin L has been shown to be upregulated in instances of muscle atrophy in both rats and mice . Additionally, our previous work investigating tendinopathy has demonstrated upregulated cathepsin activity in the tendon at 4 and 8 weeks of overuse in a rat model.…”

“…Humeral head samples ( N = 8) were analyzed by EPIC‐µCT (Equilibrium Partitioning of an Ionic Contrast‐Microcomputed tomography) based on established techniques . EPIC‐µCT involves the use of a contrast agent to better visualize less radio‐opaque tissues, such as cartilage.…”

“…Power analysis (G*Power software) was performed on prior data for both zymography ( α = 0.05, β = 0.8, Δ = 0.48) and µCT ( α = 0.05, β = 0.8, Δ = 0.75) to determine number of animals required for this study. Prior to statistical analysis, we performed a Shapiro–Wilk normality test to ensure our data were normally distributed and could undergo parametric tests.…”

Biologics and stem cell‐based therapies for rotator cuff repair

“…[26][27][28] This constriction led to degenerative changes in the tendon, evidenced by increased cellularity, rounder cell shape, and decreased collagen organization. 16,28 Subsequently, another model of overuse tendinopathy was developed using downhill treadmill running, which caused similar degenerative changes; this method can be applied either on its own [29][30][31] or in combination with an artificial subacromial impingement. 26,28 Treadmill running is noninvasive, reproducible, and mimics the local mechanical conditions of supraspinatus impingement in humans, with decreases in tendon properties.…”