Getting To Know Your Back Your spine consists of a series of small bony blocks called vertebrae. A single vertebra consists of a solid part in front (the body) and a hole behind. When lined up together, the vertebrae form the spinal canal, which contains and protects the spinal cord. Between each pair of vertebrae, there is a small opening on either side through which a spinal nerve runs. There are 31 pairs of spinal nerves, which innervate your muscles, joints and skin, enabling you to move and feel.
The vertebrae are separated and cushioned by oval pads known as discs. Each disc is composed of a tough fibrous outer layer called the annulus and a soft gel-like interior called the nucleus pulposes. In young people, the nucleus pulposes has a high water content making it a good shock absorber and load transmitter. As you age however, the disc dehydrates (i.e. it has lower water content) and becomes stiffer, hence a reduced ability for load transmission and shock absorption.
Behind the discs are small gliding joints (facet joints) which stabilise and guide movements.
Holding the vertebrae together are ligaments. Muscles surround the vertebrae, providing support for the spine. They are also responsible for producing and controlling movements of the spine.
The vertebrae and discs are shaped and arranged such that the spine is not a straight and rigid rod, but a flexible curved structure with multiple joints. There are basically four curvatures in the spine. These curvatures are important for reducing the stress on the spine while allowing you to move and yet maintain an upright posture.
Why Your Back Aches
Postural Stress Poor posture stresses your spine. When you hunch or sit in a slouched manner, ligaments are over-stretched, muscles fatigued, and discs and facet joints are under excessive pressure.
Muscle Strains Minor back muscle strains resolve quickly, but more sever strains will need treatment to relieve pain and promote healing.
Ligament Sprains Stretching ligaments too far or too quickly makes them tear and bleed into the surrounding tissues, causing swelling and pain. Sporting and motor vehicle accidents are common causes.
Arthritis Spinal joints like any other joints in the body can be affected by arthritis. Trauma and excessive load on degenerative discs/joints can cause further inflammation and the growth of bony spurs (extra bone growth due to degenerative changes), on the edges of the vertebrae.
Disc Problems Excessive pressure on discs can cause them to bulge, tear, herniate or even rupture due to injury. And because discs lose their water content and wear out with age, they are more prone to irritation and trauma due to excessive loads. Common positions and movements that put more load on the discs are sitting (especially slouched sitting), forward bending and lifting with your trunk bent.
Nerve Irritation Spinal nerves can be irritated or compressed by bulging or herniated discs and bony spurs, thereby producing pain, weakness and numbness down the legs. In a few cases, the disc herniation can be so big that it occupies the whole spinal canal and compresses on the nerves (cauda equina) causing paralysis to the muscles controlling the bladder and bowels. If you lose control over your bladder or bowel, you must see a doctor immediately!
What can you do to prevent back pain? Find out in the second part of this feature tomorrow.
AHCPR Publication 95-0642 (1994) Acute Low Back Problems in Adults: Assessment and Treatment. Clinical Practice Guideline Number 14. Agency for Health Care Policy and Research, Public Health Service, US Department of Health and Human Services.
Hides JA, Richardson CA and Jull GA (1996) Multifidus muscle recovery is not automatic after resolution of acute first-episode low back pain. Spine 21: 2763-2769.
Maher C, Latimer J and Refshauge K (1999) Prescription of activity for low back pain: What works? Australian Journal of Physiotherapy 45: 121-132.
Saal JA (1990) Dynamic muscular stabilisation in the nonoperative treatment of lumbar pain syndromes. Orthopaedic Review 19: 691-700.
Date reviewed: 6 June 2005
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