DEGENERATIVE DISC DISEASE AND LOW-BACK PAIN

Low-back pain is a very common complaint. Up to 80% of adults will experience back pain at least once in a lifetime. This pain is usually confined to the axis of the spine, i.e. it is not associated with compression or irritation of a nerve root, which results in sciatica, or leg pain.

The precise source of low back pain may vary. There are a number of tissues in the back, which are pain sensitive and may act as pain generators. The most common source of pain is the intervertebral disc. This is the shock absorber, or ball-bearing which lies between each spinal vertebra. Injury to the outer fibrous ring of the disc (annulus fibrosis) and the subsequent degeneration of the disc is a common source of back pain.

Cigarette smoking is a risk factor for disc degeneration.

Various ligaments, joints, tendons and muscles may also act as pain generators. The facet joints are small, paired joints which are positioned at the back of each disc / vertebra complex. Pain from facets joints is less common than discogenic pain and usually results in a specific clinical syndrome.

When a patient visits a medical practitioner with low-back pain, the first task of the doctor is to exclude serious underlying diseases. Although these are rare causes of back pain, certain ‘red-flags’ will alert the doctor to the possibility. ‘Red flags’ include pain in patients with a history of cancer, pain in the elderly or very young, pain that is not relieved with rest and associated symptoms of weight loss or general ill health.

The doctor’s next task is to exclude involvement or compromise of neurological tissue. Nerve root compression will result in leg pain, numbness, pins-and-needles or muscle weakness. Disturbance of bladder or sexual function are also signs of nerve root involvement.

Once serious illness or neurological compromise has been excluded, the diagnosis of ‘mechanical’ or ‘discogenic’ can be made. In the absence of nerve root involvement (i.e. simple axial back pain) there is a poor correlation between the source of the pain and the physical examination. That is, it is difficult for a doctor to determine the exact site of the pain generator by simple physical examination.

(Fig. 6 An x-ray showing a chronic degenerate disc)
(Fig.1 MRI scan showing normal intervertebral discs)
Back pain is not visible on an x-ray or scan. X-rays of the lumbar spine are performed to exclude serious causes of pain such as tumours, fractures or infections. These are uncommon causes of back pain. Plain x-rays provide very limited information about the intervertebral discs, spinal ligaments and adjacent nerve roots.
(Fig. 6 An x-ray showing a chronic degenerate disc)
A magnetic resonance image (MRI) scan provides far more information about the state of the intervertebral discs and adjacent nerve roots. These scans show the soft tissue of the spine in exquisite detail.
(Fig.1 MRI scan showing normal intervertebral discs)

The scans are expensive and should be performed at the request of a spine specialist. MRI scans are very useful for the diagnosis of nerve root compression, but are less accurate for the diagnosis of simple discogenic back pain.
Injuries to the outer fibrous ring of the disc and subsequent disc degeneration can be clearly seen on a MRI scan. However, the correlation between the scan images and the patient’s clinical picture is not always reliable. The presence of a ‘black disc’ on a scan is not necessarily confirmation of the source of the pain. ‘Black discs’ are also seen in patients with no history of back pain.
(
Fig. 3 A ‘black disc’ associated with a torn annulus)
 
Fig. 3 A ‘black disc’ associated with a torn annulus

Further diagnostic information may be gathered with provocative tests such as discography or facet joint blocks. The reliability of these tests remains controversial.

In summary, the relationship between a back pain patient’s complaints, the findings on clinical examination and the results of the special investigations (scans) remains complex and unreliable. This is one of the main difficulties in treating back pain.

TREATMENT

Low-back pain is a self-limiting disorder. The vast majority of back pain episodes settle spontaneously over a period of 3 weeks. Current advice is to remain active (prolonged bed rest is no longer advised). Acute pain can be treated with simple analgesics (Paracetamol or Codeine) or anti-inflammatories.

Once the acute pain has settled, patients may turn their attention to spine health and the prevention of recurrence. Weight loss, posture and correct lifting techniques are important. Cessation of cigarette smoking is also advised.

Specific exercises are recommended for the prevention of back pain. These involve the strengthening of the core stabilizer muscles. The transverses abdominis muscles are key core stabilizers. Physiotherapists, biokineticists and Pilates instructors can help with specific exercise regimes.

A small percentage (5-10%) of patients with acute low-back pain will go on to experience relapsing or chronic back pain. This pain may be debilitating and have a significant negative impact on patients’ quality of life. It is this group of patients who seek specialist opinion. These patients may benefit from surgery.

The surgical strategies for the treatment of chronic back pain include spinal fusion or disc replacement surgery. In spinal fusion, all movement across a disc space (motion segment) is obliterated. With disc replacement, the disc, (or pain generator), is excised and replaced with a prosthetic device that preserves motion.

Surgery is not a panacea for chronic back pain. Medical literature shows that only 2/3’s of back pain patients benefit from surgery. Surgery should be reserved as a last resort and only considered after 6 months of good non-surgical treatment

© Copyright of the South African Spine Society