Wednesday, November 18, 2009

Iliolumbar ligament under stress of slouching and the muscles that prevent it

Most biomechanical studies link the concepts of stooped postures and buckling instability of the spine under high compressive load. However everyday situations lumbar spine is subjected to small or neglectable compressive spinal load. Snijders et tried to find a mechanical cause of acute low back pain (LBP) in everyday situations. Hence their study in 2008 described strain on the iliolumbar ligaments (ILs) when slouching from standing upright.

This study show that

1. Dynamic slouching, driven by upper body weight and rectus abdominis muscle force may produce failure load of the spinal column and the ILs.
2. There is a significant increase of IL elongation with rectus abdominis muscle force.
3. Contraction of erector spinae or multifidus muscle tension ease the ILs.
4. Sudden slouching of the upright trunk may create failure risk for the spine and ILs. This loading mode may be prevented by controlling loss of lumbar lordosis with erector spinae and multifidus muscle force.

Erector spinae and multifidus muscle forces represent a bifurcation in back muscle force: one part acting on the iliac bones and one part acting on the sacrum. The multifidus muscle action on the sacrum may produce nutation which can be counteracted by pelvic floor muscles, which would link back problems and pelvic floor problems.

Snijders CJ et al; Man Ther. 2008 Aug;13(4):325-33. Epub 2007 Jun 5.

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