associated with the development of damage in musculoskeletal tissues and physiological mechanisms associated with both damage and repair of these tissues may help our ability to exert some modest degree of control over injury risk (or improved healing) in some circumstances. However, we clearly need to understand our adversary better. To start this process, we will begin by providing a brief review of some of the more common MSDs, providing descriptions and characteristic features of the disorders, prevalence and incidence data, relevant anatomy and pathology, and the risk factors or activities associated with the development of the disorders.
As can be seen below, this review focuses on MSDs affecting the low back, hands/wrists, elbows, and shoulders. While disorders affecting the hips, knees, and ankles are of interest to many musculoskeletal researchers, our emphasis is on the occupational setting, in which the former disorders tend to predominate.
Common Musculoskeletal Disorders
Low Back Pain
Description/characteristic features
LBP is a typically benign condition, though one of the most expensive conditions in industrialized countries (Mayer & Gatchel, 1988). It is associated with substantial loss in the quality of life (Punnett, 2005). LBP is characterized by pain that can range from a dull ache to a sharp, intense, and disabling pain. The focus of this pain is generally in and around the lumbar portion of the spinal column. The lumbar spine is a complex structure, consisting of vertebral bones, intervertebral discs, cartilage endplates, and nerves, and with all of these structures, there are many possible sources of pain.
LBP is often episodic, with most cases being relatively short‐lived. In fact, 40–90% of people obtain complete relief after 6 weeks (Manchikanti, 2000). LBP is often classified by duration as acute (pain lasting less than 6 weeks), sub‐chronic (6–12 weeks), or chronic (more than 12 weeks) (Koes et al., 2010). The condition may be further classified by the underlying cause as mechanical, nonmechanical, or referred pain (Manusov, 2012). While most pain is self‐limited, pain continuing after 3 months of LBP is considered chronic, as this is well beyond the 6‐ to 12‐week time period that normal connective tissues take to heal (Chawla, 2018).
Recent data suggest that approximately 38.5% of work‐related MSDs in the United States in 2016 involved the lower back (Bureau of Labor Statistics, 2018). Many occupational tasks have been associated with a higher prevalence of recurrent LBP, including lifting and/or carrying heavy weight and adoption of awkward postures such as bending, twisting, squatting, and kneeling (Amorim et al., 2019; Hoogendoorn, Poppel, Bongers, Koes, & Bouter, 1999). Exposure to whole‐body vibration in drivers (e.g., tractor drivers, taxi drivers, and helicopter pilots) appears to contribute heavily to LBP risk (Bovenzi, Schust, & Mauro, 2017), as does adoption of awkward postures when driving (Bovenzi, Schust, Menzel, Prodi, & Mauro, 2015). In the professional driving occupations cited earlier, there is also an exposure‐dependent increase in the development of degenerative changes in the spinal column, resulting in spondylolisthesis (Byeon et al., 2013; Chen, Chan, Katz, Chang, & Christian, 2004; Christ & Dupuis, 1966; Froom et al., 1984). The degenerative changes referenced earlier are thought to be due to repetitive mechanical loading and shock to the spinal column that lead to damage accumulation and degeneration (Bovenzi et al., 2017). Individual differences likely impact the effects of loading due to differences in muscle mass and strength as well as due to differences in kinematic and muscle recruitment strategies (Gallagher & Heberger, 2015; Marras et al., 2006).
Prevalence/incidence
LBP is the most common MSD with lifetime prevalence estimates ranging from 65 to 80% (Manchikanti, 2000). Approximately 9–12% of people (632 million) have LBP at any given point in time, and nearly 25% report having it at some point over a 1‐month period (Mayer & Gatchel, 1988; Waddell, 1987). Estimates of the annual prevalence of LBP range from 15 to 45% with a point prevalence of approximately 30% (Andersson, 1999). Sixty percent of those who suffer from acute LBP recover in 6 weeks and up to 80–90% recover within 12 weeks; however, the recovery of the remaining patients with LBP is less certain (Andersson, 1999).
Historical data suggest that in Americans less than 45 years of age, chronic LBP is the commonest cause of disability (Kelsey & White 3rd, 1980; Waddell, 1987). Each year, 3–4% of the US population is temporarily disabled, and 1% of the working‐age population is totally and permanently disabled by LBP (Andersson, 1999; Cunningham & Kelsey, 1984; Mayer & Gatchel, 1988). Difficulty most often begins between 20 and 40 years of age (Casazza, 2012). Men and women are approximately equally affected (“Back Pain Fact Sheet”, NINDS, 2014). LBP is more common among people aged between 40 and 80 years, with the overall number of individuals affected expected to increase as the population ages (Hoy, 2012).
Although common in the general population, there is considerable evidence that LBP risk is exacerbated by the performance of occupational tasks, and account for a significant portion of morbidity in occupational settings. A great deal of evidence suggests that heavy physical work, repetitive lifting, prolonged static work postures, bending and twisting, and exposure to whole‐body vibration likely contribute to the development of LBP (National Institute for Occupational Safety and Health [NIOSH], 1997; National Research Council – Institute of Medicine, 2001). Jobs that are highly demanding, that involve prolonged standing, and that require awkward lifting are among work‐related physical risk factors for LBP (Sterud & Tynes, 2013).
Anatomy/pathology
The lumbar spine is a complex structure composed of several different materials (see Figures 2.1–2.3), many of which have been touted as potential sources of LBP. Some of the potential pain‐generating structures include the intervertebral disk, facet (zygopophyseal) and sacroiliac joints, spinal nerve roots, and the muscles that attach to the bony processes of the vertebra (Chawla, 2018).
Figure 2.1 A motion segment of the lumbar spine.
Duckworth, T. & Blundell, C. M. (2010). Lecture notes: Orthopaedics and fractures, 4th ed., Wiley. ISBN: 978‐1‐405‐13329‐6.
Figure 2.2 Focal damage in the intervertebral disc. Fissures of grade 1 (grade 2 not shown) and circumferential tears are not likely to be symptomatic. However, grade 3 fissures are highly associated with chronic back pain. Cartilage endplate damage is also shown.
Fournier, D.E., Kiser P.K., Shoemaker, J.K., Battié, M.C., & Séguin, C.A. (2020). Vascularization of the human intervertebral disc: a scoping review. JOR Spine, 3(4): e1123. doi: 10.1002/jsp2.1123 / John Wiley & Sons / CC BY‐4.0.
Figure 2.3 Lumbar vertebrae and their facet (zygopophyseal) joints, which are the articulation of superior and inferior processes.
The intervertebral disc has been shown to be a structure capable of causing pain.
