What is the pathophysiology of muscular pain in low back pain (LBP)?

Updated: Aug 22, 2018
  • Author: Jasvinder Chawla, MD, MBA; Chief Editor: Stephen A Berman, MD, PhD, MBA  more...
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Answer

Answer

Pain receptors in muscle are sensitive to a variety of mechanical stimuli, including pressure, pinching, cutting, and stretching. Pain and injury occur when the musculotendinous contractual unit is exposed to single or recurrent episodes of biomechanical overloading. Injured muscles are usually abnormally shortened, with increased tone and tension due to spasm or overcontraction. Injured muscles often meet the diagnostic criteria for myofascial pain (MP) syndrome, a condition that Drs. Janet Travell and David Simons originally described.

MP is characterized by muscles that are in a shortened or contracted state, with increased tone and stiffness, and that contain trigger points (TrPs). TrPs are tender, firm, 3- to 6-mm nodules that are identified on palpation of the muscles. TrP palpation provokes radiating, aching pain into localized reference zones. Mechanical stimulation of the taut band, a hyperirritable spot in the TrP, by needling or rapid transverse pressure often elicits a localized muscle twitch.

Sometimes, TrP palpation can elicit a jump sign, an involuntary reflex, or flinching disproportionate to the palpatory pressure applied. MP may become symptomatic as a result of direct or indirect trauma, exposure to cumulative and repetitive strain, postural dysfunction, or physical deconditioning. MP can occur at the site of tissue damage or as a result of radicular and other neuropathic disorders at sites where pain is referred. Muscles affected by neuropathic pain may be injured due to prolonged spasm, mechanical overload, or metabolic and nutritional shortfalls.


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