Recent studies have focused on the importance of disruption of the intervertebral disc in the cause of back pain. A very plausible theory has been advanced by Maigne 3 who proposes the existence, in the involved mobile segment, of a minor intervertebral derangement (MID). He defines it as 'isolated pain in one intervertebral segment, of a mild character, and due to minor mechanical cause'. It is independent of radiological and anatomical disturbances of the segment. The most common clinical situation occurs where a vertebral level is found to be painful and yet to have a normal static and radiological appearance.
The MID always involves one of the two apophyseal joints in the mobile segment, thus initiating nociceptive activity in the posterior primary dermatome and myotome. The overlying skin is tender to pinching and rolling, while the muscles are painful to palpation and feel cord-like. Maigne points out that the functional ability of the mobile segment depends intimately upon the condition of the intervertebral disc. Thus, if the disc is injured, other elements of the segment will be affected. Even a minimal disc lesion can produce apophyseal joint dysfunction which is a reflex cause of protective muscle spasm and pain in the corresponding segment, with loss of function (Fig 33.2).
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Fig. 33.2 Reflex activity from a MID in the intervertebral motion segment. Apart from the local effect caused by the disruption of the disc (A), interference can occur in the facet joint (B) and interspinous ligament (C) leading possibly to muscle spasm (D) and skin changes (E) via the posterior rami REPRODUCED FROM C. KENNA AND J. MURTAGH, BACK PAIN AND SPINAL MANIPULATION, BUTTERWORTHS, SYDNEY, 1989, WITH PERMISSION
In theory any structure with a nociceptive nerve supply may be a source of pain. Such structures include the ligaments, fascia and muscles of the lumbosacral spine, intervertebral joints, facet joints, dura-mater and sacroiliac joints. 4
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