Corticosteroid injections by epidural or root blocks are commonly used to treat leg and back pain and may indicate that in some cases there may be an inflammatory contribution to the pain. In disc material removed from humans during operation has been found heightened levels of inflammatory chemicals which could be affected by steroid use. These inflammatory chemicals may increase degeneration of discs and sensitise the fibres of the outer disc walls. Some chemicals may also sensitise the discs by elevating reactivity of sensory nerves, inhibit the creation of new proteoglycans which hold water in the discs and may contribute to disc degeneration.
The lumbar spinal motion segments have nerve structures supplying them which can be come hypersensitised to incoming stimuli, creating pain from what would have formerly been normal sensations. Sciatic leg pain is known as nerve root or radicular pain and can be caused by irritation, inflammation or compression of the spinal nerves as they exit the spinal cord. Why nerve root pain occurs has not been established but candidates are an impoverishment of blood supply, inflammatory reactions, axon dysfunction from compression and biochemical agents. The compression that occurs may have greater effects on spinal nerve roots than other nerves and result in more significant internal nerve swelling.
The nerve may suffer from excessive inflow of fluid secondary to compression, which results in internal nerve swelling from the increased pressure. This can slow the flow through capillaries and allow fibrosis to develop in the nerve. Nutrition to the spinal nerve roots comes via the cerebrospinal fluid to the tune of about 60% and nerve fibrosis interferes with this, making the nerve more responsive and perhaps more likely to suffer compression symptoms due to the increased reactivity of the nerves. Blocking or reducing the blood supply can cause pain in these nerves, unlike the more usual loss of motor and sensory functions in compression of peripheral nerves.
Quick development of compromise to the nerve and its blood supply is more likely to produce the onset of nerve root symptoms than a slow development. This may explain how many older people appear to have compromised nerve exits but do not suffer symptoms. An inflammatory reaction ensues if disc material is placed in the epidural space and disc material may cause nerve injury when in contact with it. Other possibilities are that tumour necrosis factor (TNF) may be involved as injection of this agent into the nerves causes similar changes that occur in nerve root compromise. An inflammatory or auto-immune response to the normally inaccessible nuclear disc material has also been proposed. Many factors may be responsible overall.
The facet joints are synovial joints, like our finger joints, and are formed from articular processes on an upper and a lower vertebra. Facet joints react to injury and damage in the same way as our other joints react, with pain, stiffness, loss of movement, muscle spasm and eventually degeneration. As the discs degenerate the facet joints follow by becoming osteoarthritic. The fibrous capsules which surround the facet joints are rich in nerve endings and injections into the joints have been shown to refer pain into the arms, upper back and legs. Facet joints are capable of generating pain and have been shown experimentally to be involved in significant percentages of patients with neck, thoracic and lumbar pain.
The main posterior joints between the pelvis and the sacrum are the sacroiliac joints, large synovial joints which have been shown to refer pain to the buttock, low back, leg and groin. Chronic low back pain sufferers, in an experimental setting, were shown to have this joint involved in their pain production in 2-30% of cases. Muscular tissue also has pain receptors which react to pressure and stretching as well as other stimuli. If muscles are stretched suddenly under pressure or are overworked over a period of time they will become painful, shortened and exhibit
Myofascial pain sydrome has been described in injured or posturally abnormally used muscles, whereby muscles have an increased degree of contraction and so-called trigger points. Trigger points are firm, tender nodules felt on palpation in the muscle tissue and such palpation causes pain to radiate into local well defined areas.
Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about
Physiotherapists, physiotherapy,
physiotherapists in Leeds, back pain, orthopaedic conditions, neck pain and injury management. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.
