Bone health

Bone Physiology:

Your body is made up of 206 bones. These bones are the protective and supportive framework of your body and have many functions. Your bones are responsible for storing nutrients, minerals and lipids; producing blood cells for nourishment and helping to protect against infection.

There are two types of bone – cortical bone and trabecular bone. Eighty percent of your skeletal mass is made up of cortical bone, also called compact bone. Cortical bone forms a protective outer shell around every bone in your body. Trabecular bone, also called cancellous bone, represents 20 percent of the skeletal mass. This type of bone contains red and yellow bone marrow cells in the center of the bone. Trabecular bone is less dense and more elastic, making up most of the bone tissue in your skull, ribs and spine. Both types help to form the long and short bones in your body.

As you grow older, your bones go through a remodeling, where old bone is replaced with new bone. There are two kinds of cells that help with this process – osteoblasts, which are bone-forming cells; and osteoclasts, which are bone-destroying cells. Remodeling increases bone strength by adding new bone tissue when needed and enables calcium stored in the bone to be removed for metabolic purposes. Remodeling also allows excess calcium to be returned to the bone reservoir for later use. This process also occurs during the repair of broken bones.

Assessment of Bone Health:

You can assess your bone health through a bone density scan—the best noninvasive way to determine the strength of your bones. The bone density scan measures the bone mineral density, which is where 60 to 80 percent of bone strength is derived. The test is performed at the hip and lumbar spine (sometimes at the forearm), and the diagnosis is based on the results. A bone density scan should be performed (if you don’t have any risks) at age 65 and older for women, and 70 and older for men. However, if you are at risk, it should be done earlier.

Once you receive the results of your bone density exam, you should weigh the results of three sections: bone mineral density (BMD), the T-Score and Z-Score. Bone mineral density quantifies your bone mass BMC (amount of calcium) divided by the area it was measured. It is compared to two reference populations to derive the T-Score and Z-Score. T-Score is the comparison of the results with young adults of the same sex at the time of peak bone mass.  A woman will be compared to a young Caucasian (your ethnicity does not matter) female, age 20 to 30. Men are compared to young adult males. The Z-Score is the comparison with individuals of the same age and ethnicity from a reference database.

If the bone density scan determines that you have a low bone mineral density, you are at a high risk for fractures. Osteoporosis diagnosis is based on T-Scores for post-menopausal women and men, age 50 and older.

The World Health Organization (WHO) established the criteria for diagnosis of osteoporosis based on known fracture levels for Caucasian, post-menopausal women. The T-score results are used to define the different categories.

Diagnosis T-Score
Normal -1.0 and higher
Osteopenia or low bone mass Between -1.0 and -2.5
Osteoporosis -2.5 and lower
Severe osteoporosis -2.5 and lower with fracture

The diagnosis is based on the lowest T-Score among the lumbar spine, total hip, or the area called the femoral neck.

FRAX Score

You can also determine your risk for fractures through your FRAX score if you have low bone density and have not taken osteoporosis medicine. For more information about the FRAX score, visit riskcalculator.fore.org.