When we look at bone closely, we can see there are 2 types of bone structure: either a dense form called cortical bone or a lattice-like form called spongy bone.
Cortical bone forms the hard outside layer of all bones in the body and makes up most of the skull and ribs. Spongy bone is mainly found inside the vertebrae (the bony segments of the spinal column), and inside the ends of long bones like the femur (thigh bone). In the following drawing of a normal thigh bone, you can see cortical bone along the outside of the shaft of the bone, and spongy bone inside the end of the bone, near the hip joint.
Bone is a living tissue that is in a state of constant turnover. Cells within the bone called osteoblasts are involved in forming new bone, while cells called osteoclasts resorb bone. (When bone is resorbed calcium and other minerals are removed from bone tissue and released into the circulation.) Both osteoblast activity and osteoclast activity are needed to maintain healthy bone tissue. The balance between these 2 opposing activities within bone is influenced by several factors, including:
Other conditions that you may have, as well as certain medications that you may be taking, such as corticosteroids, can also influence your bone health.
If the amount of bone being formed is greater than the amount of bone being resorbed, then your bone mass — the amount of bone in your skeleton — will increase, as occurs during childhood. However, around the age of 30, the amount of bone being resorbed begins to become slightly greater than the amount of bone being formed, and for many years after this age, this slight imbalance leads to a gradual loss of bone mass as you age.
If you are a woman, the menopause is a significant event in terms of your bones. The drop in the level of the female hormone oestrogen causes a marked decrease in bone mass after the menopause. The likelihood that this bone loss leads to thinner, weaker bones and increased fracture risk — a condition called osteoporosis — is increased if you have one or more known risk factors for osteoporosis, such as being of Asian or Caucasian background, having another family member with osteoporosis, a light build and a diet deficient in calcium throughout your life.
Although it is more common in women, men can also develop osteoporosis and also be prone to the fractures that can occur as a result of having this condition.
When your bones have thinned to the point that osteoporosis is diagnosed, the physical structure — and soundness — of your bones has changed. In particular:
These changes can mean you are more likely to have a fracture.
You may be at an increased risk of osteoporosis if your parents have a history of fractures.
If you have needed to take medications that have the side effect of reducing bone mass (for example, cortisone), or you have another illness that directly or indirectly causes a loss of bone mass (for example, an eating disorder or systemic lupus erythematosus in women, you may also be at increased risk of developing osteoporosis.
In osteoporosis, your bones are thin and brittle, and can break more easily. Common sites for a fracture because of osteoporosis include the wrist, the hip and the vertebrae of the spine. Some people with osteoporosis can have a fracture because of a light bump or an increase in pressure, for example, sneezing can cause a rib fracture in someone with osteoporosis.
A fracture in the spine can occur because of compression of the weakened bone, which in osteoporosis can happen during the simple motion of bending forward or lifting. This type of fracture in the spine can lead to pain and a marked curving of the spine with an associated loss of height that is often seen in older women with osteoporosis.
A fracture of the hip due to a fall can lead to an inability to walk unassisted for a prolonged period, a loss of independence, long-term nursing care and an increased likelihood of dying during the year following the fracture.
Osteoporosis can go unnoticed for many years unless a fracture occurs. It is therefore important to discuss your bone health with your doctor as you get older, even if you have not experienced a fracture.
To help enhance bone formation, all people — especially women who have gone through menopause — should:
Last Reviewed: 08 July 2009
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