The stress-strain relationships of human spinal ligaments and muscles indicate that the spinal musculature play a major role in spine stability (1, 2). Low-loading rate, quasi-static assessments of posteroanterior (PA) spinal stiffness have correlated increased PA spine stiffness to voluntary contracture of the lumbar extensor muscles (3, 4), No study, however, has examined the contributions of lumbar extensor muscle and high-loading rate dynamic PA spinal stiffness. The objective of this study was to quantify PA dynamic spinal stiffness at rest and during maximal voluntary contraction (MVC) efforts in patients with LBP. Twenty-two consecutive patients with LBP underwent dynamic spinal stiffness assessment in the prone resting position and during lumbar extensor muscle MVC, A hand-held Activator Adjusting Instrument equipped with an impedance head was used to deliver high-loading rate( < 0,1 msec) PA manipulative thrusts (450 N) to the L3 spinous process for spinal stiffness assessment using a previously validated technique (5). Surface, linear enveloped, electromyographic (sEMG) recordings were obtained during the thrusts from electrodes (8 leads) located over the L3 and L5 erector spinae and data was normalized to subject individual MVC’s. The accelerance (peak acceleration/peak force, kg-1) or stiffness index was calculated for each of the thrusts and compared for the resting and active MVC trials using a 2-tailed, paired t-test. A significantly increased spine stiffness index (8.36%) (P=0.012) was found upon MVC trials compared to prone resting stiffness indices. Lumbar spine extensor MVC contributes to increased PA lumbar spine stiffness. These findings corroborate the findings of others and add support to the significance of the trunk musculature in providing spinal stability.
Reference: Christopher J. Colloca, D.C.1, Tony S. Keller, Ph.D. 2 Daryn E. Seltzer, D.C.3, Arlan w. Fuhr, D.C.1; Muscular and Soft-Tissue Contributions of Dynamic Posteroanterior Spinal Stiffness; Proceedings of the International Conference on Spinal Manipulation, Bloomington, MN September 21-23,2000.
1 Postdoctoral & Related Professional Education Department Faculty, Logan College of Chiropractic, St. Louis, MO, USA; National Institute of Chiropractic Research, Phoenix, AZ, USA; Private Practice of Chiropractic, Phoenix, AZ, USA. 2 Professor, Department of Mechanical Engineering & Department of Orthopedics and Rehabilitation, The University of Vermont, Burlington, VT, USA. 3 National Institute of Chiropractic Research, Phoenix, AZ, USA; Private Practice of Chiropractic, Phoenix, AZ, USA.