There are four prime reasons for backache, and these can occur singly or in any combination:

1. A damaged or degenerated disc can bulge at the edges when under extreme pressure. This can squeeze against the posterior ligament of the spine which is pain-sensitive.
    

2. The rear portion of the vertebrae form the articular facets of the spinal joints. Like any other joint in the human body, the membrane which lines the inside of them is richly supplied with sensory nerves and can become swollen and inflamed. This results in pain.
    

3. Muscle spasm produced by faulty posture, injury or strain can itself cause pain. If there is also disc degeneration present, the vice-like pressure of the muscle spasm will cause disc compression and subsequent ligament pain as well.
    

4. Acute pain caused by pressure on a nerve root is also the fault of degenerated disc. Usually in this type of back pain the wall of the disc loses its natural elastic quality and the soft jelly in the centre of the disc bulges out. A slight bulge of hernia presses on the posterior ligament as it type 1., but a more severe bulge, or a broken-off fragment of disc can cause pressure on the nerve tissue and acute pain. This pain sometimes travels down one leg, or both, giving rise to the condition known as sciatica. This can result in numbness, pins and needles, abnormal nerve reflexes and loss of muscle strength. This type of nerve pain often produces pain in the other areas as well - ligaments, joints and muscles.