Assessments of spinal stiffness are becoming more popular in recent years as a objective biomechanical means to evaluate the human frame. Studies investigating posteroanterior (PA) forces in spinal stiffness assessment have shown relationships to spinal level, body type, and lumbar extensor muscle activity. Such measures may be important determinants to discriminate between patients with low back pain and asymptomatic subjects. However, little objective evidence is available discerning variations in PA stiffness and its clinical significance. No study has investigated the relationships of invivo PA spinal stiffness to radiographic images. L5-S1 disc to body height ratios were calculated from digitized plane film lateral radiographs of eighteen symptomatic LBP patients (8 females and 10 males, 15-69 years, mean 44.3 SD 15.4 years). Posterior disc height ratio (PDR) and anterior disc height ratio (ADR) were compared to the L5 posterior-anterior dynamic effective stiffness determined using a validated in vivo mechanical impedance assessment procedure [1]. Dynamic effective stiffness (N/m) was calculated from the impedance-frequency response spectrum as the dynamic mechanical impedance (Force/Velocity, Ns/m) x circular frequency (rad/sec). Dynamic effective stiffness (minl) at the first resonance frequency (fminl)is reported. No correlation was noted between minl and ADR at L5. However, minl was positively correlated to the PDR at L5 {minl=232 x PDR + 32 (R=0.76)}. Dynamic spinal stiffness assessments may provide additional biomechanical data that may be prove to be of use to clinicians in the diagnosis of lumbar spinal disorders.
Reference: Christopher J. Colloca,DC; Tony S. Keller,PhD; Terry K. Peterson,DC; Daryn E. Seltzer,DC; Arlan W. Fuhr,DC. Proceedings of the International Conference on Spinal Manipulation , Sept 21-23,2000.
