Musculoskeletal Disorders. Sean Gallagher
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process of the ulna), while the roof is made of elastic connective tissue (a retinaculum). This retinaculum has a variable structure (and may even be missing) with variations in its tightness perhaps also contributing to cubital tunnel syndrome (O’Driscoll, Horii, Carmichael, & Morrey, 1991).
Risk factors/activities associated with cubital tunnel syndrome
Although more studies are needed, known risk factors for cubital tunnel syndrome include work that involves holding the elbow in a flexed position for long periods, particularly when on a hard surface (Cutts, 2007), performing repetitive tasks with high force requirements (Fadel et al., 2017), and performing repetitive tasks with vibratory tools (Cutts, 2007). The prevalence for cubital tunnel syndrome is also higher in workers over 50 years of age and in those who have worked for more than 1 year in the job (thus, duration) (Saito et al., 2018; van Rijn et al., 2009). Obesity and presence of diabetes may also increase the risk, particularly for a mechanical double crush of the ulnar nerve (Cutts, 2007).
Hand‐arm Vibration Syndrome
Characteristics/description
Hand‐arm vibration syndrome (HAVS) is a disorder associated with exposure to HAV, usually as the result of the prolonged use of powered hand tools. HAVS can be a painful and potentially disabling condition, with symptoms including pain, numbness, tingling, and nerve dysfunction. These symptoms can affect the hands, wrists, and forearms and may interfere with sleep. HAVS may also lead to a pallor or cyanosis of the fingers as well as numbness, tingling, and pain. Episodes typically last 5–30 min; however, the duration and severity of symptoms may increase with disease progression. Musculoskeletal symptoms can include decreased grip strength and, in some cases, Dupuytren’s contractions—a condition in which fingers in the hand (usually the two fingers farthest from the thumb)—are permanently contracted and cannot be fully straightened out.
Epidemiology
HAV is defined as the transfer of vibration from a tool to a worker’s hand and arm. The amount of HAV is characterized by the acceleration level of the tool when grasped by the worker and in use. The vibration is typically measured on the handle of tool while in use to determine the acceleration levels transferred to the worker. HAVS was first widely recognized as a potential occupational hazard in the mid‐1980s. However, the earliest reports of vibration white finger (VWF) were provided in the early 1900s in miners and quarry workers (Laws, 1998). It was only later realized that musculoskeletal and neurologic symptoms were part of the same syndrome. Although the prevalence in the general population is very low, the prevalence in those experiencing prolonged HAV exposure can be as large as 50% and varies with the intensity of the exposure. Risk appears to be increased somewhat in countries with colder climates (Shen & House, 2017). Exposed workers typically exhibit symptoms in middle age, though symptoms can be observed in younger workers with more intensive exposures. The latency period between exposure and symptoms can be quite broad, ranging from less than a year to four decades, depending on the intensity of exposure.
Anatomy/pathology
The tissue damage associated with exposure to HAVS may affect vascular, neurologic, and musculoskeletal structures in the hands, wrist, or forearm. Damage to these various systems may progress at different rates (Pelmear, 2003). The vascular component is also known as VWF and is related to Raynaud’s phenomenon, which is the most recognized manifestation of HAVS. The precise pathological mechanism is not totally clear; however, it is believed that vibration exposure causes endothelial damage through mechanical trauma and oxidative stress, leading to vasoconstriction through activation of the sympathetic nervous system. Nerve fibers (both myelinated and nonmyelinated) are thought to be damaged through vibration exposure. Musculoskeletal symptoms may be due to direct damage to musculoskeletal tissues due to the repetitive forces of vibration and/or may be secondary to nerve damage (Shen & House, 2017).
Risk factors/activities associated with HAVS
Sources of vibration that can cause HAVS are varied and include hand drills, chisels, power chain saws, power jigsaws, sanders, riveters, polishing tools, and many others. There is some indication that high‐frequency vibration is more relevant to the symptoms of HAVS, as such vibration may be absorbed preferentially by the hand and fingers, whereas lower frequency vibration energy may affect the arms and shoulders to a greater extent (Shen & House, 2017). It is a disorder resulting from prolonged exposure to vibration, specifically to the hands and forearms while using vibrating tools. Symptoms include numbness, tingling, and loss of nerve sensitivity. HAVS is a painful and potentially disabling condition of the fingers, hands, and arms due to vibration. There is initially a tingling sensation with numbness in the fingers. The fingers then become white and swollen when cold and then red and painful when warmed up again. Cold or wet weather may aggravate the condition. Picking up objects such as pins or nails becomes difficult as the feeling in the fingers diminishes, and there is loss of strength and grip in the hands. The pain, tingling, and numbness in the arms, wrists, and hands may interfere with sleep.
Commonalities Among MSDs
If one contemplates the summaries of the various MSDs summarized in Table 2.1, certain commonalities become apparent. One is that all appear to be associated with the development of damage to musculoskeletal tissues (and/or other structures). It should not be surprising that these disorders, all of which result can result in significant pain and dysfunction, would be associated with tissue damage. Another consistent refrain is that all of these disorders are associated with exposure to the repetitive application of stress, sometimes expressed in terms of exposure to forceful and repetitive exertions. Adoption of non‐neutral postures is another potential source of repeated stress, as such postures generally serve to increase stress on affected tissues in some form or fashion (and may be adopted frequently). Sometimes, the repeated stress comes in the form of vibration exposure, which has been associated with damaging impacts on musculoskeletal tissues, along with other associated tissues.
Table 2.1 Summary of Common MSDs
| Disorder | Involved structures |
|---|---|
| Low back pain | Degeneration and inflammation in many potential tissue sources, including intervertebral discs, facet and sacroiliac joint, spinal roots, and muscles attached to the vertebrae |
| Hand & wrist tendinopathy | Degenerative changes in extensor pollicis brevis and abductor longus tendons (sheath breakdown, nodularity, tendon fraying) |
| Lateral tendinopathy of the elbow | Degenerative changes in common extensor tendons at the elbow (microtears that lead to partial or complete rupture) |
| Medial tendinopathy of the elbow | Degenerative changes in common flexor tendons at the elbow (increased collagen remodeling and mucoid ground substance) |
| Shoulder tendons (rotator cuff injuries) | Degeneration and inflammation in rotator cuff tendons |
| Muscle fatigue | Many potential contributors, including physiological changes that lead to an energy crisis, dysfunction in calcium homeostasis, neurological changes (altered neuromuscular junctions), and apoptosis |
| Myalgia (muscle pain) | Many potential contributors, including dysfunction in calcium homeostasis and increased inflammation |
| Muscle fibrosis |
Increased extracellular matrix production, for example, |