Myofascial Factors in Low Back Pain

PATHOPHYSIOLOGY

The development of MPS is often associated with postural derangements, such as muscle overload, dystonia, and fatigue. Postural abnormality (e.g., scoliosis) may reflect asymmetric extensor or flexor tone in a group of paraspinal muscles. Secondary causes of myofascial pain are extremely common, including painful spasm with spondylolisthesis or increases in tone with emotional stress. The most common cause of myofascial trigger point (MTrP) formation is repetitive stress on individual muscles or muscle groups. In the low back, a small hemipelvis or short leg may lead to MPS.

An MTrP is a hyperirritable spot within skeletal muscle associated with a hypersensitive palpable nodule in a taut band. Here the key pathophysiologic abnormalities are principally located at the muscle center near its motor end-plate zone. Precipitating factors may facilitate acetylcholine release at motor end plates, causing sustained muscle fiber contractions, release of vascular and neuroactive substances, and muscle pain perpetuating the muscle spasm. The abundance of the nociceptors in muscle, joints, skin, and blood vessels explains the pain severity and exquisite muscle tenderness upon palpation. Possibly, the chronicity of MPSs is attributable to altered sensory processing as characterized by central sensitization with alteration in supraspinal inhibitory descending pain-control pathways.

CLINICAL MANIFESTATIONS

Characteristic MPS symptoms begin after discrete trauma or insidiously. Patients note varying degrees of regional deep aching sensations. Functional complaints include decreased work tolerance, impaired muscle coordination, stiff joints, fatigue, and weakness, leading to sleep disturbances, mood changes, and stress. The most reliable physical signs of trigger points are pain recognition, taut band, tender point, referred pain, and local twitch response. MTrPs usually appear in muscular structures used for posture maintenance, including quadratus lumborum, gluteus maximus, gluteus medius, iliocostalis, iliopsoas, levator ani, longissimus thoracis, lower rectus abdominis, multifidi, piriformis, and hip rotators. With low back pain, quadratus lumborum, used for trunk stabilization and posture, is the most common source of MTrP. Palpation of MTrP will reproduce or increase regional pain, possibly eliciting referred, radiating pain patterns. Sometimes MTrP activation may evoke autonomic phenomenon, including dermal flushing, lacrimation, sweating, and temperature changes. Chronic MTrP patients require evaluation for postural abnormalities, ergonomic factors, and hypothyroidism.

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