Causes of low back pain
Low back pain can be separated into three main groups:
1. Mechanical back pain (pain is caused by the structures of the lumbar spine or sacroiliac joint)
2. Nerve root pain, commonly referred to as “sciatica” (due to compression or irritation of the nerve roots)
3. Serious disease
About 90-95% of cases of low back pain are due to mechanical back pain and another 5% due to nerve root pain. Only a very small minority (less than 1%) are due to serious causes.
1. Mechanical Low Back Pain
Pain from the lumbar disc can be severe and is usually felt in the midline of the low back but can radiate into the lower abdomen, groin, buttock and leg. Pain can be felt on all activities and movements but is particularly severe on sitting and lifting when the pressures within the disc are higher. Disc pain often follows the course of severe episodes of pain, which can last for various lengths of time, interspersed with a background discomfort and a feeling of low back weakness. Disc pain can affect people of all ages and is the most common cause of low back pain in the young and middle-aged adult. See segmental instability.
Facet joint pain
Facet joint pain is rarely felt exclusively in the midline of the low back. It can be felt on one or either side and can radiate into the groin and lower leg. Pain tends to be worse on prolonged standing, when the facets are compressed due to the body’s weight. It can occur at all ages but is one of the more common sources of pain in older people. See segmental instability.
Sacro iliac pain
Sacro iliac pain is not felt in the midline of the low back and is usually felt over the low back dimple and buttock. Pain can again radiate into the groin or lower leg. Sacroiliac pain is more common in women and can often first occur during pregnancy. See sacroiliac instability.
Postural back pain
In some instances, pain may be felt in the low back without there being any significant abnormality. Pain may be felt on prolonged sitting, standing or walking and may be relieved by changing activity or position. It may be that in such instances pain is felt from the ligaments of the spine which are in a position of stretch, but which are not truly injured.
2. Nerve root pain
Depending on which nerve root is being compressed or irritated, pain may be felt anywhere in the groin or leg. Groin or leg pain tends to be worse than back pain. Compression can cause the nerve to not function properly, leading to numbness, pins and needles or tingling or weakness of the leg, ankle or foot muscles. See prolapsed intervertebral disc.
Cauda Equina Compression
Some nerve roots supply the bowels, bladder and genitals and if these are compressed then this can cause loss of sensation in the saddle area (the area of the body that would be in contact with a saddle if sitting on a on a horse) and loss of function of the bowel and bladder, i.e. not being able to pass water or motions, incontinence and not being able to achieve an erection. Thankfully this is an uncommon situation but if it occurs it must be regarded as an emergency and immediate medical advice should be sought.
3. Other causes
Thankfully, more serious causes of back pain are rare and represent less than one in a hundred cases of low back pain. These include serious conditions affecting the spine, such as fracture, infection, inflammation (as part of a more widespread inflammatory disease such as rheumatoid arthritis) or cancer. Alternatively, pain in the back may be felt from other conditions and organs in the abdomen. Most of these can be ruled out at an early stage by your doctor when he talks to you and examines you. Suspicion of something more serious may be aroused if there are other problems associated with your back pain, such as weight loss, fever, a feeling of being generally unwell or pain that does not alter with movement.