The Identification And Prevention Of Low Back Disorders. Part 4

May 16th, 2012 · No Comments ·

For the sake of retaining reasonable length to this article it must be sufficient to state that the lumbar region of the human spine is subject to enormous and continuous mechanical forces which create an increased likelihood of potential injury.

Lumbar Function

Lumbar function has been described in the literature in hundreds of books and thousands of articles. However, until very recent developments in the fields of non-invasive imaging and biomechanics, the actual involvement of the lumbar spine with regard to its role and response to muscular stimulation, i.e. movement, has been impossible to specifically ascertain. The primary function of the lumbar region is the movement of the torso in relation to the pelvis. Although often misstated in the literature, the movement in the lumbar region is limited to extension. The normal lumbar spine cannot rotate and cannot, technically, flex. The shape and the mechanical relationship of the spinal facets from the sacrum up to and including the eleventh thoracic vertebra (T 11) prevent rotational functional on a longitudinal plane.

In published reports which indicate vertebral rotation in the lumbar area, no real immobilization of the pelvis was reported. The pelvis can rotate and cadavers can be rotated in the lumbar area but the lumbar spine of a living subject can not be significantly rotated without producing damage. The muscles, ligaments and facets of the lumbar area are designed to produce four functions:

Lumbar extension,
Prevent lumbar rotation,
Limit lumbar flexion and
Limit lateral bending.

The muscles of the buttocks and thighs can rotate the pelvis around the heads of the femur and therefore produce corresponding movement in the lumbar region. It might be interesting to note that the lumbar spine moves even in the absence of lumbar muscle contraction.

None of the aforementioned mechanical information is of any practical value unless the following two points are clearly understood:

It is widely held that extension (of the spine) produces compression forces on the lumbar discs by reducing the vertical distance between the vertebrae at the rear, thus compressing the discs and
In reality, extension actually INCREASES the disc space along the rear face of the vertebrae. Therefore, instead of increasing the forces on the discs (all other factors remaining equal), extension REDUCES the forces on the discs!

The practical significance of these two points is rather simple. Causes of low back injuries may have been historically misdiagnosed and rehabilitative protocols may, in fact, exacerbate existing c nditions.

Lumbar Function Versus Back Extension

Traditionally, lumbar function was synonymous with back extension with regard to the measurement of strength and range of motion. In most cases the isolation of the lumbar spine was neglected when testing was performed and the action of the back extension measured resulted from a significant contribution of the buttocks (gluteal group, maximus and minimus) and the thigh biceps or hamstring groups (semitendinosus, semimembranosus and biceps femoris). The aforementioned is not an exercise in irrelevant kinesiological braggadocio because while it is certainly true that lumbar function is usually involved in back extension, it is also true that back extension is primarily the result of the muscles that move the pelvis in relation to the legs (the hip extensors).

Until and unless these hip extensor muscles are removed from the equation, lumbar function cannot be accurately measured. It is normally the power of these large muscle groups which expose the lumbar area to forces which supersede the momentary potential of the lumbar muscles. The basic mechanical cause of low back injury is the “weak link” status of the lumbar muscles. If a solution to low back injuries is to be developed, practical solutions to these mechanical problems must be achieved. While many may not be interested in exactly how and why something works, or why something does not work” in this instance it is very important to understand both the solutions and the problems”.

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