Low back pain is located from the belt line and 30 cm above and into the buttocks. Sometimes the back pain is accompanied by referred pain to groin and legs.
The lower back has 5 vertebrae. Each bony vertebra has two joints separated by a disc which acts as a spacer and shock absorber for the spine which is supported by ligaments and muscles. A nerve exits at each vertebra level in the spine.
Back pain results when one or combination of the above structures are injured and inflamed, which can result in a trapped nerve e.g. sciatica.
Leg pain can occur when the disc protrudes and irritates the nerve
Strenuous activity that often includes a combination of bending, twisting and lifting can cause the inner gel of the disc to bulge on to the nerve.
If the nerve is irritated or trapped, pain, numbness, pins and needles can be felt in the leg, calf or foot depending on which nerve is trapped. Sciatica is the most common condition which produces pain down the back of the leg and femoralgia produces pain in front of the leg.