A Trigger Point (TrP) is a hyperirritable spot, a palpable nodule in the taut bands of the skeletal muscles’ fascia. Direct compression or muscle contraction can elicit jump sign, local tenderness, local twitch response and referred pain which usually responds with a pain pattern distant from the spot.
Jump sign is the characteristic behavioral response to pressure on a TrP. Individuals are frequently startled by the intense pain. They wince or cry out with a response seemingly out of proportion to the amount of pressure exerted by the examining fingers. They move involuntarily, jerking the shoulder, head, or some other part of the body not being palpated. A jump sign thus reflects the extreme tenderness of a TrP. This sign has been considered pathognomonic for the presence of TrPs.
Local twitch response – defined as a transient visible or palpable contraction of the muscle and skin as the tense muscle fibers contract when pressure is applied. Coursed by needle penetration or by transverse snapping palpation.
Referred pain, also called reflective pain, is pain perceived at a location other than the site of the painful stimulus. Pain is reproducible and does not follow dermatomes, myotomes, or nerve roots. There is no specific joint swelling or neurological deficits. Pain from a myofascial TrP is a distinct, discrete and constant pattern or map of pain with no gender or racial differences able to reproduce symptoms – referred pain map.