A Clinical and Pharmacologic Review of Skeletal Muscle Relaxants for Musculoskeletal Conditions

Abstract

Muscle strains and other musculoskeletal disorders (MSDs) are a leading cause of work absenteeism. Muscle pain, spasm, swelling, and inflammation are symptomatic of strains. The precise relationship between musculoskeletal pain and spasm is not well understood. The dictum that pain induces spasm, which causes more pain, is not substantiated by critical analysis. The painful muscle may not show EMG activity, and when there is, the timing and intensity often do not correlate with the pain. Clinical and physiologic studies show that pain tends to inhibit rather than facilitate reflex contractile activity. The decision to treat and choice of therapy are largely dictated by the duration, severity of symptoms, and degree of dysfunction. Trigger point injections are sometimes used with excellent results in the treatment of muscle spasm in myofacial pain and low-back pain. NSAIDs are used with much greater frequency than oral skeletal muscle relaxants (SMRs) or opioids in the treatment of acute MSDs. Unfortunately, remarkably little sound science guides the choice of drug for the treatment of acute, uncomplicated MSDs, and the evaluation of efficacy of one agent over another is complicated by numerous factors. Only a limited number of high-quality, randomized, controlled trials (RCTs) provide evidence of the effectiveness of NSAIDs or SMRs in the treatment of acute, uncomplicated MSDs. The quality of design, execution, and reporting of trials for the treatment of MSDs needs to be improved. The combination of an SMR and an NSAID or COX-2 inhibitor or the combination of SMR and tramadol/acetaminophen is superior to single agents alone.