Electromyographic reflex responses to mechanical force, manually assisted spinal manipulative therapy

Study Design. Surface electromyographic reflex responses associated with me chanical force, manually assisted (MFMA) spinal manipulative therapy were a nalyzed in this prospective clinical investigation of 20 consecutive patien ts with low back pain. Objectives. To characterize and determine the magnitude of electromyographi c reflex responses in human paraspinal muscles during high loading rate mec hanical force, manually assisted spinal manipulative therapy of the thoraco lumbar spine and sacroiliac joints. Summary of Background Data. Spinal manipulative therapy has been investigat ed for its effectiveness in the treatment of patients with low back pain, b ut its physiologic mechanisms a re not well understood. Noteworthy is the f act that spinal manipulative therapy has been demonstrated to produce consi stent reflex responses in the back musculature; however, no study has exami ned the extent of reflex responses in patients with low back pain. Methods. Twenty patients (10 male and 10 female, mean age 43.0 years) under went standard physical examination on presentation to an outpatient chiropr actic clinic. After repeated isometric trunk extension strength tests, shor t duration (<5 msec), localized posteroanterior manipulative thrusts were d elivered to the sacroiliac joints, and L5, L4, L2, T12, and T8 spinous proc esses and transverse processes. Surface, linear-enveloped electromyographic (sEMG) recordings were obtained from electrodes located bilaterally over t he L5 and L3 erector spinae musculature. Force-time and sEMG time histories were recorded simultaneously to quantify the association between spinal ma nipulative therapy mechanical and electromyographic response. A total of 16 00 sEMG recordings were analyzed from 20 spinal manipulative therapy treatm ents, and comparisons were made between segmental level, segmental contact point (spinous vs. transverse processes), and magnitude of the reflex respo nse (peak-peak [p-p] ratio and relative mean sEMG). Positive sEMG responses were defined as >2.5 p-p baseline sEMG output (>3.5% relative mean sEMG ou tput). SEMG threshold was further assessed for correlation of patient self- reported pain and disability. Results. Consistent, but relatively localized, reflex responses occurred in response to the localized, brief duration MFMA thrusts delivered to the th oracolumbar spine and SI joints. The time to peak tension (sEMG magnitude) ranged from 50 to 200 msec, and the reflex response times ranged from 2 to 4 msec, the latter consistent with intraspinal conduction times. Overall, t he 20 treatments produced systematic and significantly different L5 and L3 sEMG responses, particularly for thrusts delivered to the lumbosacral spine . Thrusts applied over the transverse processes produced more positive sEMG responses (25.4%) in comparison with thrusts applied over the spinous proc esses (20.6%). Left side thrusts and right side thrusts over the transverse processes elicited positive contralateral L5 and L3 sEMG responses. When t he data were examined across both treatment level and electrode site (L5 or L3, L or R), 95% of patients showed positive sEMG response to MFMA thrusts . Patients with frequent to constant low back pain symptoms tended to have a more marked sEMG response in comparison with patients with occasional to intermittent low back pain. Conclusions. This is the first study demonstrating neuromuscular reflex res ponses associated with MFMA spinal manipulative therapy in patients with lo w back pain. Noteworthy was the finding that such mechanical stimulation of both the paraspinal musculature (transverse processes) and spinous process es produced consistent, generally localized sEMG responses. Identification of neuromuscular characteristics, together with a comprehensive assessment of patient clinical status, may provide for clarification of the significan ce of spinalmaanipulative therapy in eliciting putative conservative therap eutic benefits in patients with pain of musculoskeletal origin.