Viscoelastic stresses on anisotropic annulus fibrosus of lumbar disk under compression, rotation and flexion in manual treatment

Chaudhry, Hans; Ji, Zhiming; Shenoy, Nigel; Findley, Thomas

doi:10.1016/j.jbmt.2007.06.001

« Previous Next »Journal of Bodywork and Movement Therapies
Volume 13, Issue 2 , Pages 182-191, April 2009

Viscoelastic stresses on anisotropic annulus fibrosus of lumbar disk under compression, rotation and flexion in manual treatment

Hans Chaudhry, PhD
- Department of Biomedical Engineering, New Jersey Institute of Technology, Newark, NJ 07102, USA
- Department of Physical Medicine and Rehabilitation, New Jersey Medical School, UMDNJ, Newark, NJ, USA
Zhiming Ji, PhD
- Department of Mechanical Engineering, New Jersey Institute of Technology, Newark, NJ 07102, USA
- Corresponding author. Tel.: +19735963341; fax: +19736424282.
Nigel Shenoy, MD
- Department of Physical Medicine and Rehabilitation, New Jersey Medical School, UMDNJ, Newark, NJ, USA
Thomas Findley, MD PhD
- Department of Physical Medicine and Rehabilitation, New Jersey Medical School, UMDNJ, Newark, NJ, USA
- Center for Healthcare Knowledge Management, VA Medical Center, East Orange, NJ 07018, USA
- Department of Biomedical Engineering, New Jersey Institute of Technology, Newark, NJ 07102, USA

Received 30 November 2006; received in revised form 1 March 2007; accepted 14 June 2007.

Summary

Background

Twisting (spinal rotation) and bending (flexion) are commonly reported as triggers for low back pain. This paper addresses whether the twisting stress on the annulus fibrosus of the lumbar disk is greater or less than the bending stress for the same angle of twist or bending.

Methods

Stress–strain relation for transversely isotropic material is applied to the transversely isotropic annulus fibrosus of the lumbar disk to analyze the viscoelastic stresses produced due to 6% compression, 10° twist and 10° bending.

Findings

The bending stress is 450 times greater than the twisting stress for the same angle of twist or bending of the annulus fibrosus. The twisting and bending moments increase two-fold in quick maneuvers lasting 0.1s (as in high velocity manipulations), compared to slow maneuvers lasting 60s.

Interpretation

From biomechanical perspective, in situations where both flexion and spinal rotation occur, the stress on the intervertebral disk is markedly higher with flexion compared to rotation. In patients with low back pain that has a disk mediated (discogenic) component, manipulation and mobilization therapies should avoid flexion to minimize stress on the disks. This is particularly relevant for high velocity manipulations where the stress on the disk is doubled for both flexion and rotation. The results in this paper can help guide manual therapists to adjust their treatments to minimize stress on the intervertebral disk.

Keywords: Lumbar disk, Annulus fibrosus, Compression, Flexion, Rotation, Twist, Bending, Viscoelastic stress