Variations in posteroanterior stiffness in the thoracolumbar spine: Preliminary observations and proposed mechanisms

Background and Purpose. Evaluation of posteroanterior (PA) movement in the spine is commonly used in the clinic, but little is known about the mechanisms involved. The purposes of this study were to examine variations in PX stiffness along the thoracolumbar spine and to investigate possible factors that might determine the pattern of stiffness. Subjects. Twenty-one pain-free volunteers (10 male, 11 female), aged 18 to 41 years (X = 26.6, SD = 7.5), participated. Methods. Posteroanterior stiffness was measured at 5 locations (L4, L1,T10, T7, T4), together with various subject characteristics. Results. Mean PA stiffness varied among locations, with the greatest stiffness at L4 (13.3 N/mm) and the lowest stiffness at L1 (10.4 N/mm). A relatively small but important, proportion (22% or less) of the variance in stiffness data at some vertebral levels was accounted for by the variables describing subject characteristics. Conclusion and Discussion. Posteroanterior stiffness varies along the spine in a manner consistent with the nature of support for the spine. The observed pattern of variation of PA stiffness along the spine appears to be influenced by some factors other than those relating to the spine. [Lee M, Steven GP, Crosbie J, Higgs RJED. Variations in posteroanterior stiffness in the thoracolumbar spine: preliminary observations and proposed mechanisms.