Part 1: Analysis of 2-stepTraction: FE modeling

Kyungsoo K et al J Phys Ther Dec(6) 2014                                                                                                                                           

Discussion

The biomechanical effects of two-step traction on the lumbar spine were investigated. During global axial traction, the intradiscal pressures at all MSUs (motion units) decreased and this resulted in increased stress on the fibers of the annulus fibrosus in the posterior region. The stress on the fibers of the annulus fibrosus in the posterior region was higher for the L4–L5 and L5–S1 MSUs than for the other MSUs. The results of the current study may explain why protrusion during excessive traction can occur. When the annulus fibrosus is weakened by degeneration and/or herniation, it could be damaged more easily by stress concentration, especially at the L5–S1 MSU. Axial traction therapy should be used with caution in patients with intervertebral disc damage at the L4–L5 and/or L5–S1 MSUs. Thus, 1/3 BW was assumed ideal for global axial traction in this study. Previously published experimental studies have shown that extension motion increases intradiscal pressure at the intervertebral discs (Sato et al., 1999, Rohlmann et al., 2001). Thus, proper local decompression helps decrease the risk of intervertebral disc damage and increases the beneficial effects of reduced intradiscal pressure. Typically, up to half of a patient’s body weight has been used for axial traction force however, No studies have documented the force transmitted through the vertebrae, intervertebral discs, and ligaments, and the translation of the vertebrae during traction and local decompression is also unknown.

Comment: part 2 will discuss what the researchers did and its clinical relevance.