There are two basic types of pain. Nociceptive pain results from direct trauma which can be either mechanical, thermal, or chemical. If the trauma is mechanical in nature, it may manifest itself as muscle pain. Examples include sprains, bone fractures, burns, bumps, bruises, inflammation, and obstructions. Neuropathic pain results from damage to the peripheral or central nervous system tissue or from abnormal processing of pain in the central nervous system (Wilkie, Brown, Corless, Farber, Judge, Shannon, et al, 2001). Examples include post-shingles neuralgia, nerve trauma, components of cancer pain, phantom limb pain, carpal tunnel syndrome, and widespread nerve damage (most commonly caused by diabetes or chronic alcohol use).

Pain is more than a simple annoyance; it can lead to serious physical and psychological consequences across almost every bodily system. Further, if acute pain continues without adequate relief, it can become neuropathic pain, in which the normal pain pathways become altered, making it much more difficult to treat (Wilkie et al, 2001).

It is widely hypothesized that people with disabilities experience more pain with greater severity than the non-disabled population; however, data supporting this hypothesis have not yet been systematically examined or summarized (Chetwynd, Botting, & Hogan, 1993; Ehde, Jensen, Engel, Turner, Hoffman, & Cardenas, 2003).