A method to test contractility of the supraspinatus muscle in mouse, rat, and rabbit

Abstract

The rotator cuff (RTC) muscles not only generate movement but also provide important shoulder joint stability. RTC tears, particularly in the supraspinatus muscle, are a common clinical problem. Despite some biological healing after RTC repair, persistent problems include poor functional outcomes with high retear rates after surgical repair. Animal models allow further exploration of the sequela of RTC injury such as fibrosis, inflammation, and fatty infiltration, but there are few options regarding contractility for mouse, rat, and rabbit. Histological findings can provide a "direct measure" of damage, but the most comprehensive measure of the overall health of the muscle is contractile force. However, information regarding normal supraspinatus size and contractile function is scarce. Animal models provide the means to compare muscle histology, imaging, and contractility within individual muscles in various models of injury and disease, but to date, most testing of animal contractile force has been limited primarily to hindlimb muscles. Here, we describe an in vivo method to assess contractility of the supraspinatus muscle and describe differences in methods and representative outcomes for mouse, rat, and rabbit.

Impaired contractile function of the supraspinatus in the acute period following a rotator cuff tear

“…Tendon transection resulted in supraspinatus muscle retraction of approximately 5 mm (Fig. 1a ) by day 2, or almost 20% of resting muscle length in the rat supraspinatus [ 74 ]. There was no further change in muscle shortening over time, but the tendon scarred down by day 15, in such a way that the space between the tendon and insertion site was filled by a fibrous-connective tissue, forming an ill-defined “pseudo-tendon” that reattaches the muscle to the humeral head (Fig.…”

“…Contractile function of the supraspinatus muscle was measured in vivo as described previously [ 74 ]. Briefly, in the anesthetized animal, the scapula was immobilized in a custom designed rig as described previously [ 74 ] and the tendon of the supraspinatus muscle was released and attached to a load cell (FT03, Grass Instruments, Warwick, RI & QWLC-8 M, Honeywell, Morris Plains, NJ). The suprascapular nerve was stimulated via subcutaneous needle electrodes (36BTP, Jari Electrode Supply, Gilroy, CA) placed at the suprascapular notch.…”

Assessing Rat Forelimb and Hindlimb Motor Unit Connectivity as Objective and Robust Biomarkers of Spinal Motor Neuron Function

“…Forelimb grip is one measure that can assess muscle function, but grip (similar to the clinical score) can only assess the cumulative effects of upper and lower motor neuron dysfunction and thus suffers from limitations previously mentioned in the clinical motor score 54 . Invasive in situ contractility measuring techniques can be applied to the rat forelimb muscles but were not included as they are terminal experiments and are not suitable for longitudinal assessment 55 . Second, we chose to investigate the SOD1 rat model as a validation of our technique, but we did not define the full natural history of motor unit loss in this model.…”

Fatty Infiltration Is a Prognostic Marker of Muscle Function After Rotator Cuff Tear

“…The power calculation was based on a minimal detectable difference of 2.295 N, with an expected 0.86 SD of residuals, for a desired power of 0.8 and alpha value of .05, based on previously published data. 57 Twelve rabbits completed both contractile testing and histology, which were used for correlational and regression analyses retrospectively.…”

“…Contractile function of the isolated supraspinatus muscle was measured in anesthetized animals as described previously. 57 Briefly, the tendon of the supraspinatus muscle was released and attached to a load cell. The suprascapular nerve was stimulated via subcutaneous needle electrodes (J05 Needle Electrode Needles, 36BTP; Jari Electrode Supply) placed at the suprascapular notch.…”