Читать книгу Musculoskeletal Disorders - Sean Gallagher - Страница 54

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, collagen and fibronectin
Carpal tunnel syndrome (median mononeuropathy)	Median nerve entrapment, irritation, inflammation
Ulnar tunnel syndrome (ulnar mononeuropathy)	Ulnar nerve entrapment
Hand‐arm vibration syndrome	Many potential sources, including damage to vascular, neurological, and/or musculoskeletal structures of the hand, wrist, and forearm

Whenever one observes damage development in a material exposed to repeated mechanical stress, there is one mechanism that comes to mind that would explain how and why this damage is occurring. This process is, of course, material fatigue failure. Fortunately, the fatigue failure theory has been around since the 1840s, and much is known regarding the response of materials to repeated stress (Stephens, Fatemi, Stephens, & Fuchs, 2001). However, the fact that musculoskeletal tissues are located in a dynamic biological environment, in which exposed materials have a healing capacity, provides an important wrinkle in the development of biological tissue damage. This provides us with competing processes that will control musculoskeletal tissue damage development. Unless some new and unique mechanism of damage development from repeated stress is discovered that applies only to biological materials, we must assume the damage part of the equation is controlled by the mechanism of fatigue failure. We know certain aspects regarding the healing portion of the equation, as well, but much more needs to be learned.

This book examines the development of MSDs as a process of fatigue failure of musculoskeletal tissues, but one modified by complex physiological and biochemical processes (including, but not limited to, tissue healing). To our knowledge, no one has considered such an approach toward understanding the causes of musculoskeletal tissue damage nor for understanding how we might better control MSDs and improve overall musculoskeletal health. We acknowledge at the outset that there is much yet to be learned about this extremely complex process. However, there is much that is known, which may improve our understanding regarding the development and control of MSDs.