Understanding the lower back
Most of the lower back is made up from muscles that attach to, and surround, the spine. The spine is made up of many bones called vertebrae. The vertebrae are roughly circular and between each vertebra is a 'disc'. The discs are made of strong rubber-like tissue which allows the spine to be fairly flexible. Strong ligaments also attach to adjacent vertebrae to give extra support and strength to the spine. The various muscles that are attached to the spine enable the spine to bend and move in various ways.
The spinal cord, which contains the nerves that come from the brain, is protected by the spine. Nerves from the spinal cord come out from between the vertebrae to take and receive messages to various parts of the body.
What are the types of low back pain?
Simple low back pain
This is the most common type. About 19 in 20 cases of acute (sudden onset) low back pain are classed as 'simple low back pain'. (It is sometimes called 'non-specific' low back pain.) Simple low back pain means that the pain is not due to any underlying disease that can be found. In some cases the cause may be a sprain (an over-stretch) of a ligament or muscle. In other cases the cause may be a minor problem with a disc between two vertebrae, or a minor problem with a small 'facet' joint between two vertebrae. However, these causes of the pain are impossible to prove by tests and so it is often impossible for a doctor to say exactly where the pain is coming from, or exactly what is causing the pain.
Sometimes a pain may develop immediately after you lift something heavy, or after an awkward twisting movement. Sometimes you can just wake up with low back pain.
Simple does not mean that the pain is mild - the pain can range from mild to very bad. Typically, the pain is in one area of the lower back, but sometimes it spreads to the buttocks or thighs. The pain is usually eased by lying down flat, and is often made worse if you move your back, cough, or sneeze. So, simple back pain is 'mechanical' in the sense that it varies with posture or activity.
Most bouts of simple low back pain improve quickly, usually within a week or so. In about 3 in 4 cases, the pain has either gone or has greatly eased within four weeks. In about 9 in 10 cases the pain has gone or has greatly eased within six weeks. However, once the pain has gone it is common to have further bouts of pain (recurrences) from time to time in the future. Also, it is common to have minor pains 'on and off' for quite some time after an initial bad bout of pain. In a small number of cases the pain persists for several months or longer (chronic back pain).
Nerve root pain
This occurs in less than 1 in 20 cases. This means that a nerve coming from the spinal cord is irritated or pressed on. (This is often referred to as a 'trapped nerve'.) You feel pain along the course of the nerve. Therefore, you may feel pain down a leg to the calf or foot, and the pain in the leg or foot is often worse than the pain in the back. A common example is 'sciatica'. This is where a main nerve to the leg, the sciatic nerve, is irritated or pressed on.
Nerve root pain can range in severity from mild to very bad. Like with simple low back pain, nerve root pain is often eased by lying down flat, and is often made worse if you move your back, cough, or sneeze. The irritation or pressure on the nerve may also cause pins and needles, numbness or weakness in part of a buttock, leg or foot.
The cause of the irritation or pressure on a nerve may be due to inflammation caused by a ligament or muscle sprain. A 'slipped disc' is another well known cause. (A disc does not actually 'slip'. What happens is that part of the inner softer part of the disc bulges out (prolapses) through a weakness in the outer harder part of the disc. The prolapsed part of the disc can press on a nerve nearby. See separate leaflet called 'Prolapsed Disc' for details.). Other less common conditions can press on a nerve to cause nerve root pain.
Less common causes of low back pain
Arthritis (inflammation of the joints) of the spine sometimes causes back pain. Osteoarthritis is the common form or arthritis and usually occurs in older people. Ankylosing spondylitis is another form of arthritis that can occur in young adults and causes pain and stiffness in the lower back. Rheumatoid arthritis may affect the spine, but you are likely to have other joints affected too. (There are separate leaflets on each of these types of arthritis.)
Various uncommon bone disorders, tumours, infections, and pressure from structures near to the spine occasionally cause back pain. (Less than 1 in 100 cases of low back pain.)医学.全在线www.med126.com
How can I tell what type of back pain I have?
Most cases of low back pain that develop suddenly (acutely) are due to simple low back pain. Many people just 'get on with it' and treat it themselves - and indeed most get better quickly. However, if in doubt, see your doctor for a check-over and advice.
As a general guide, if any of the following occur then it may indicate that it may not be simple low back pain, and there may be a more serious underlying cause such as a nerve root problem, or another disorder. Therefore, tell a doctor if you have any of the following.
Cauda equina syndrome - rare, but an emergency
Cauda equina syndrome is a particularly serious type of nerve root problem. This is a rare disorder where the nerves at the very bottom of the spinal cord are pressed on. This syndrome can cause low back pain plus: problems with bowel and bladder function (usually unable to pass urine), numbness in the 'saddle' area (around the anus), and weakness in one or both legs. This syndrome needs urgent treatment to preserve the nerves to the bladder and bowel from becoming permanently damaged. See a doctor immediately if you develop these symptoms.
