Mechanisms for Pain and Injury in Musculoskeletal Disorders - Fundamentals and Assessment Tools for Occupational Ergonomics - page 395

TABLE 16.1 Factors Affecting Pain Outcomes
Mechanical Factors
Injury parameters
—Magnitude (load and deformation)
—Direction
—Rate
—Duration
Initial geometry (configuration) of anatomical structure
Loading frequency (i.e., repetitive or single application)
Responses of specific anatomical structures (i.e., individual tissue responses)
Physiological Factors
Anatomic features (i.e., geometry, stenosis, etc.)
Inflammation (pre-existing)
Degeneration (pre-existing, tissue and neural circuit)
Electrophysiological sensitivity
Electrophysiological preconditioning before injury
Immunological preconditioning before injury
Confounding Factors
Genetics
Gender
Age
Comorbidities
Psychological
Psychosocial and environmental issues
Inferences can be made in light of these findings for painful MSDs. For example, epidemiologic studies
indicate that patients with pre-existing spinal degeneration at the time of injury, experience more severe
and longer lasting neck pain symptoms. 41,42,49 It is possible that such degeneration can contribute to
inflammatory changes in the facet joint, which may increase this joint's susceptibility to mechanical
injury. Therefore, when undergoing motions or loading, which may not normally elicit nociceptive
changes, the pain fibers may be sensitized and fire under mechanical conditions, which are much less
severe than previously required to initiate nociception. The same may be true for degenerative
changes in other tissues. In this light, it may further be possible that repetitive loading of tissues at nor-
mally noninjurious level, when sustained over many times, can lead to painful outcomes or lowered
thresholds for stimulating painful injury.
Additional geometric and anatomic factors contributing to pain risk are gender, existing spinal
degeneration, stenosis, and genetics 48 (Table 16.1). For example, for the case of whiplash, females
experience increased symptom persistence when compared to males. 48 The anatomical considerations
specifically related to gender, which include decreased neck muscle strength and spinal canal size, add
support to the role of neck mechanics in affecting a pain mechanism. Moreover, anecdotal evidence
has shown that smaller spinal canal size is associated with more symptomatic responses in whiplash. 41
Similar geometric constraints of anatomy also apply to regions of the body such as the wrist (i.e.,
carpal tunnel syndrome). Finally, more recent clinical research into spinal pain in general has shown
that genetics may play a very key role in pain persistence for a given injury, accounting for many discre-
pancies observed among different patients for seemingly similar injuries. 13 Future research into neck pain
mechanisms would be strengthened if it considered the role of genetics in many of the issues discussed in
this chapter.
16.4 Implications for MSD: Applications and Future Research
Emerging out of this discussion, a number of areas of research focuses, which remain to be investigated
are identified for painful MSD. From the broad coverage presented earlier, it can be appreciated that