Musculoskeletal Disorders. Sean Gallagher

Musculoskeletal Disorders - Sean Gallagher


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Partial and full tears in supraspinatus tendons, a rotator cuff tendon. (a) The location of the supraspinatus tendon. (b–d) X‐ray images of a partial‐thickness tear in the supraspinatus tendon. In a neutral position (b), a partial tear was not evident; hence, changes were interpreted as tendinosis. Crass position (c) and modified Crass position (d) show a hypoechoic region (arrows) interpreted as a partial tear in a fat‐suppressed T2‐weighted magnetic resonance image. (e and f) Full‐thickness tear (arrows) of a supraspinatus tendon (arrows). Neutral position (e), Crass position (f), and modified Crass position (g).

      Modified from Shah, N. P., Miller, T. T., Stock, H., & Adler, R. S. (2012). Sonography of supraspinatus tendon abnormalities in the neutral versus Crass and modified Crass positions: A prospective study. Journal of Ultrasound in Medicine, 31(8), 1203–1208. doi: 10.7863/jum.2012.31.8.1203. Wiley.

      High shoulder pain prevalence is often seen in athletic pursuits, particularly those requiring forceful and repetitive motions that involve throwing or other activities where the hands and/or elbows are active above the level of the shoulder. High stresses are placed on the shoulder in activities such as baseball pitching, football throwing, tennis, volleyball, and swimming. These repetitive high‐stress activities are likely to result in microdamage and damage propagation that may exceed the repair capacity of shoulder musculoskeletal tissues (Bani Hani et al., 2021).

      Upper Extremity Muscle Disorders: Fatigue, Myalgia, and Fibrosis

      Characteristics/description

      Muscle fatigue denotes a transient decrease in the force and power capacity of skeletal muscle activity (Enoka & Duchateau, 2008). Repetitive or sustained contraction of skeletal muscle can lead to a progressive and reversible loss in the ability to produce the desired force (Allen, Lamb, & Westerblad, 2008; Ortenblad, Lunde, Levin, Andersen, & Pedersen, 2000). Myalgia is also known as muscle pain and is a symptom of many diseases and disorders, including prolonged repetitive work (Bongers, Ijmker, Heuvel, & Blatter, 2006; Hadrevi et al., 2019; Sjøgaard, Lundberg, & Kadefors, 2000). Muscle fibrosis is characterized by fibroblast and myofibroblast cell proliferation and excessive accumulation of extracellular matrix proteins in fascial tissues, such as collagen and fibronectin (Contreras, Rebolledo, Oyarzun, Olguin, & Brandan, 2016; Fisher et al., 2015). Muscle fibrosis is also associated with increased muscle pain (Fisher et al., 2015; Pavan, Stecco, Stern, & Stecco, 2014), presumably as a secondary consequence of nerve pain receptors becoming enmeshed in the fibrosing fascial tissues (Fisher et al., 2015; Pavan et al., 2014).

      Epidemiology

      Prolonged standing work and intense training are associated with MSDs and muscle fatigue is considered a precursor to MSDs (Garcia, Laubli, & Martin, 2015; Hadrevi et al., 2019). However, the myriad of underlying possible reasons muscle fatigue discussed in the following section makes epidemiological studies difficult. Work‐related muscle pain (myalgia) is considered a public health problem causing otherwise healthy individuals to end up on sick leave (Holtermann, Hansen, Burr, & Sogaard, 2010). Neck pain is one of the more common MSDs, with over 30% of individuals experiencing some degree of discomfort in the neck over a lifetime (Cohen, 2015; Cote, Cassidy, & Carroll, 1998). Most episodes of acute neck pain will resolve with or without treatment, but nearly 50% of individuals will continue to experience some degree of pain or frequent occurrences. A “tissue fibrosis” hypothesis is supported by clinical studies examining biopsies from patients with chronic MSDs (Dennett & Fry, 1988; Ettema, Amadio, Zhao, Wold, & An, 2004; Hirata et al., 2005).

      Anatomy/pathology

Schematic illustration of a model for possible early and late events in muscle response to a repetitive high repetition high force (HRHF) upper extremity task for 6 weeks.
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