Back pain (rachialgia) may occur when the intricate arrangement of bones, ligaments, discs, muscles and nerves that makes up the back becomes strained, torn, broken, stretched or otherwise disrupted.
The most common cause of back pain is ligamentous and muscular damage from incorrect lifting. Lifting and twisting simultaneously is particularly dangerous. A poor posture can also add to muscular and ligamentous strain.
In older people, arthritis may be the cause, when the smooth joints between the vertebrae become roughened and damaged by age and long years of use. This is osteoarthritis, but rheumatoid arthritis, which normally affects the hands and feet, may also affect the back.
A slight shift in the position of one vertebra on another, or inflammation of the surrounding tissues, may put pressure on a nerve, causing sciatica (leg pain) or localised back pain.
Direct injuries may fracture or dislocate the bones in the back, causing the spinal cord to be pinched, and paralysis of the body below that point.
There are discs of rubbery material between each vertebra that act as shock absorbers and allow movement between the discs. These intervertebral discs may be damaged by a sudden injury, gradual deterioration with age or many years of heavy work. A damaged disc may bulge (slipped disc) and press on a nerve as it leaves the spinal cord, to cause pain in both the back and down the course of that nerve. Discitis is an inflammation of the disc that causes local pain without pressing directly on a nerve.
Fibromyositis occurs in large muscles that have been overused and damaged repeatedly by heavy work or exercise. Scattered muscle cells are replaced by fibrous scar tissue to disrupt the structure of the muscle and cause a deep ache that worsens with use.
Osteoporosis is a thinning of the bones that occurs mainly in women after the menopause, due to a lack of calcium in the bones. It may result in bones breaking easily anywhere in the body, but particularly in the back where the weak vertebrae may collapse and cause pain.
Any woman who has been pregnant will confirm the distressing pain that may be caused by that condition. Hormonal changes cause the ligaments throughout the body to slacken, and when this occurs in the back the vertebrae can shift slightly to cause considerable pain.
Menstrual period pain is a common cause of lower back pain, particularly in younger women who have not been pregnant.
Psychological and psychiatric conditions, including anxiety and depression, may cause muscle spasms and inappropriate perception of minor aches and pains that are magnified into a significant problem.
Other causes of back pain include scoliosis (a sideways curvature of the spine), posterior facet syndrome (small joints at back of vertebra are inflamed), Paget disease (in which the bones enlarge and soften in the back, legs and skull), Scheuermann’s disease (an inflammation of the vertebrae in the centre of the back that is common in teenagers), hip disorders (eg. osteoarthritis, poor circulation) may be felt as a pain in the back, diffuse idiopathic spinal hyperostosis (spines on vertebrae) and ankylosing spondylitis (a long-term inflammation of the small joints between the vertebrae in the back).
Cancer from one part of the body to another is called metastatic carcinoma, and the back is one site where these spreading cancers may lodge.
Back pain does not necessarily come from the back. Many diseases of the organs in the chest and belly may cause back pain. Conversely, quite severe damage to the back may cause pain anywhere from the belly to the big toe, without any pain being actually felt in the back.
A woman’s organs of reproduction are a common source of back pain. Infections of the Fallopian tubes (salpingitis) or uterus (pelvic inflammatory disease) may be felt in the back, as may endometriosis, a twisted ovarian cyst, and a prolapsed uterus (uterus slips down into the vagina).
There are also many less common causes of back pain.