Root blocks or epidural injections, using corticosteroids, are routine treatments for leg and back symptoms and may support the hypothesis that there is an inflammatory aspect to the patient’s pain. Operative removal of human disc material has been analysed to find increased concentrations of inflammatory mediators which might respond to the steroid treatment. Changes which can occur from inflammatory substances include increasing the sensitivity of sensory nerves in the outer annular walls of the discs, limiting the production of proteoglycan molecules which hold water in the discs and adding to the effects of disc degenerative processes.
The motion segments of the lumbar spine contain nerve structures which can become over-sensitive and over-reactive, leading to painful sensations resulting from what were previously painless mechanical inputs. Radicular pain or nerve root pain is leg pain which may be the result of compression, inflammation or irritation of one of the nerve roots emerging from the spinal cord. The underlying pathology of nerve root pain is not clear, with suggestions being biochemical activators, inflammation, compromised blood supply and dysfunction of the axons secondary to compression. Compression injuries and internal swelling may be more likely to occur in spinal nerve roots due to their structure.
If compression increases the tendency of the nerve to allow fluids across its membranes then oedema can result as too much fluid enters the nerve. This increased internal nerve pressure may block blood flow in the capillaries and lead to fibrosis developing in the nerve. Spinal nerve roots achieve around 60% of their nutrition from the cerebrospinal fluid and any fibrosis around the nerves can reduce this, making the nerves hyper-responsive and so more vulnerable to compression. Loss of blood throughput or slowing of the flow may induce nerve changes which generate pain rather than the loss of feeling followed by loss of muscle control which follows compression of a peripheral nerve.
If the nerve and its vascular supply are compromised quickly then nerve root symptoms are more likely than with a slow onset, perhaps giving a clue to why older people do not suffer such symptoms despite compromise of the nerve exits. Disc material has been experimentally placed in the epidural space of dogs and found to generate a significant inflammatory reaction and may cause damage to nerves when in contact with them. If TNF (tumour necrosis factor) is injected into a nerve it causes similar changes to those which ensue after nerve root compromise. An auto-immune reaction to the internal disc material, which is not normally accessible, has also been proposed but it is likely that many aspects are relevant.
The spinal facet joints are formed from a joint process of a vertebra above and one below and are synovial joints like many other bodily joints. These joints respond to damage and injury like the rest of our joints and exhibit stiffness, pain, movement loss, muscle spasm and finally degenerative changes. The facet joints develop degenerative changes secondary to the changes which occur in the disc segments themselves. The facet joint capsules, well innervated fibrous bags, have been shown experimentally by injection to be able to refer pain into the legs, thoracic spine and arms, depending on their location. Established sources of pain, facet joints are known to be involved in large proportions of neck, lumbar and thoracic pain.
The sacro-iliac joint between the pelvis and the sacrum is a large synovial joint known to refer painful and other symptoms to the groin, the leg, low back and buttock. In patients with chronic low back pain, experimental testing has shown involvement of the sacroiliac joint in their pain problems in from two to thirty percent of cases. Pain receptors exist in muscular tissue also and respond to stretching and pressure as well as other inputs. If muscles are overburdened either repetitively or in a strain at one point they will respond by shortening, increasing their tension and being painful.
A described muscle pain problem is myofascial pain syndrome, in which muscles are regularly used incorrectly or have been damaged develop tightness and trigger points. Trigger points can be palpated in the muscles as tender and firm tissue areas which then refer pain out into well known nearby regions.
You must log in to post a comment.