A disc is a small cushion composed of a thick gel contained in a tough membrane. This cushion is firmly attached between each of the vertebrae of the spine. The term "slipped disc" does not refer to a disc which has literally slipped out of place. Instead, it means that some of the gel-like contents of the disc either:
- bulge outwards, like a weak spot in a tyre,(herniation) or
- is extruded through a tear in the membrane which normally encases it
This bulge or extruded tissue causes local inflammation, and may press on nearby nerves, causing back pain symptoms.
Acute disc herniation occurs more in younger people, aged 30 - 40, when the disc pulp is still gel-like. With age, the pulp hardens, and is less likely to herniate. In older people, degenerative disc changes are more likely to cause problems.
Any part of the spine can be affected, and the cervical spine (neck) is involved in 8% of cases. The commonest site is at the level C5-C6 and C6-C7, that is between the 5th and 6 th, or 6 th and 7 th neck vertebrae respectively. These constitute 70% of cases.
Cervical spondylosis (narrowing of the openings for the nerves and spinal cord) is the result of degeneration of the cervical spine discs, together with osteophyte formation (spurs of bone growing on the vertebrae). The disc space becomes narrowed, and its degenerated contents may be squeezed outwards, causing the same problems as acute disc herniation in young people. The main difference lies in the more gradual onset of symptoms. Older patients tend to have problems at several levels of the spine.
Apart from physical pressure on surrounding tissues, there is also local inflammation, which causes pain at the site of the disc problem.
Symptoms and causes
Both herniation and spondylosis produce pain and other symptoms: herniation suddenly and the other more gradually. The site and nature of the pain will vary according to which nerves, if any, are compressed or irritated.
Acute disc herniation in younger people is classically sudden in onset, and often associated with a particular activity, such as sports, trauma or sudden twisting of the neck in normal activities. There is a sudden pain, usually at the back of the neck, though pain may be referred to the shoulder or elsewhere depending on which nerve root is involved. Other symptoms may be
- pins and needles
- muscle weakness
- diminished reflexes
of the muscle whose nerve is being compressed by the disc.
If the spinal cord is being compressed, symptoms may be
- abnormal gait (difficulty walking)
- neurological signs as above in the legs
- weakness or loss of normal bladder and bowel function
Diagnosis and tests
Examination usually shows muscle spasm, tenderness and a decrease in the range of motion of the neck. A full neurological examination is needed to determine loss of sensation, weakness and test reflexes. These findings indicate which level of the spine is likely to be the site of disc problems.
Plain X-rays of the spine, some taken in special views, will show problems with the bones, for example osteophytes in degenerative disease.
MRI , however, is the best way to show disc problems.
Most disc problems are managed conservatively at first, with good results. Treatment consists of
- pain management - non-steroidal anti-inflammatories work well
- rest or activity modification - a soft collar is useful
- heat and massage can relieve pain
- intermittent traction may be needed
- physical therapy for rehabilitation, once pain-free and function is resumed -special emphasis is placed on neck and shoulder muscle strengthening
- selective nerve root injection with steroids and local anaesthetic may help
Treatment is continued for 6-8 weeks, and the patient is reassessed. If there is no improvement, surgery may be considered.
Urgent surgery is indicated in the following conditions:
- severe neurological symptoms
- failure to improve despite intensive conservative treatment
- symptoms which worsen during conservative treatment
The type of operation done will depend on the problems shown on MRI. In some cases, laminectomy alone is done, in others it is combined with excision of the disc and spinal fusion.
Most patients respond well to conservative management, and only a small percentage will require surgery. When correctly done, surgery is highly successful in relieving symptoms, and provides long-term relief.