PAIN IN THE BACK AND REFERRED PAIN

It is common for pain to be felt in an area much larger than the site of the injury, in remote tissues, which apparently have nothing wrong with them. This is called referred pain, and its mechanism is not well understood, but it probably occurs because the perception of pain can be felt as being anywhere in the network supplied by a particular nerve root. Information about any part of that region of the body reaches the brain along the same neural route. That is why people are able to feel pain in ‘phantom’ limbs that have been amputated. The pain message from the nerves in the stump are interpreted as if coming from a whole limb.

Pain in the back-Any of the tissues of the spine can be a source of pain except for the discs and the cartilage of the facet joints which have no nerve supply. If the pain arises in the more superficial muscles, it can be identified as coming from a particular spot. Pain from around the facet joints and ligaments is less easy to pinpoint; and if it arises as the effect of a ruptured disc, it is felt too diffusely to locate precisely. When it is the nerve root that is irritated, pain can be felt anywhere in the region which that nerve supplies. Thus, pain from injury to the sacral or lumbar nerve roots may be felt in the lower back or to one side, or, very often, down one leg on the same side as the nerve. Disturbance to cervical or upper thoracic nerve roots may produce similar symptoms in an arm. Pain from the waist region is often felt in a buttock or groin. Similarly, pain originating in the ligaments and joints of the lumbar spine may be felt across the back of the hips, round the groin, across the buttocks, along the thigh to the knees or even further down the leg.

A sufferer’s doctor or physiotherapist should be helped to identify the level in the spine of the source of pain by an exact description of where the pain is felt and its nature.

Root involvement; nerve root lesion-These are medical terms for the condition in which a nerve root is being irritated by being compressed or angulated, so that its blood supply is restricted. As well as pain, there may be other symptoms; if the nerve is of the motor type, whose function is to stimulate muscles into activity, the affected muscle may become weak, and have a reduced reflex response. It is seldom that all the nerves of a nerve root are damaged: as a rule, only a small proportion of them is affected.

Constant irritation of the nerve root in its dural sleeve may set up inflammation throughout the surrounding tissues, and this can cause adhesions to form between the walls of the spinal canal and the dural tube which sheathes the spinal cord, and also in the intervertebral foramina, the facet joints of the vertebrae, and the surrounding ligaments. These adhesions prevent the nerve root from moving easily in and out through its foramen with the normal movements of the spine and limbs, and this may cause pain. If a disc prolapses backwards, the prolapse can, depending on the size of the spinal canal, involve the cauda equina itself. This is rare, but if it happens, the resulting back and leg pain, with numbness, weakness and disturbance of bowel and bladder function, creates a surgical emergency.

Other symptoms-Pain may be accompanied by other symptoms, such as a feeling of dullness or heaviness, or perhaps coldness or a tingling sensation. When a lumbar nerve root is irritated or compressed, there may be weakened muscles as well as pain; a loss of sensitivity in the skin of the leg and the foot; pins and needles; tingling, heaviness, constriction or cramp.

When the spinal canal in the lumbar spine is constricted (spinal canal stenosis) so that there is pressure on the spinal cord, or when the bundle of nerve roots in the Cauda equina or blood vessels are compressed, the symptoms, in addition to pain, may include weakness in the legs, so that walking becomes difficult, and weakness of the bladder and bowels, even incontinence, may result. Medical help should be sought without any delay.

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