DEXA scans (dual energy x-ray absorptiometry) is the test we use to measure bone density. The result is reported as a T-score, which is a way to compare a patient’s bone density to a normal young population. Because bone density varies according to race and gender, different normal populations are used. A T score between 1 and -1 indicates that your bone density is within the range of 90% of the 26 year old normal population of your reported race and gender.

If you Tscore is below -1.5 you are said to have osteopenia. If it is below -2.5 you have osteoporosis. This means weak bone. These cutoff levels are arbitrary. The lower your bone density, the higher your fracture risk. Osteoporosis, unlike osteoarthritis, is not painful. Pain occurs when a bone breaks. Bone density gradually decreases for the entire population with age. Women can have a more rapid rate of decline in their bone density for the first 5 years after onset of menopause. All women should have a baseline DEXA scan when they start menopause and this should be repeated at least once 2 years later.

To better understand osteoporosis I will use the analogy of high blood pressure. Neither condition is typically symptomatic. Left untreated, these conditions will eventually lead to severe medical problems; heart attack and stroke on the one hand, and fractures on the other. Both conditions can be treated to prevent later complications. Numerous medications are now available to treat low bone density. There is not complete agreement at which point treatment should be recommended.

I obtain DEXA scans on every patient on whom I perform a joint replacement operation. The cost is low ($150). We have found that this test is very predictive of certain complications that can develop after surgery. Sometimes even very young patients can have low bone density. In hip resurfacing we use the result in determining the risk of postoperative femoral neck fracture and determining how to precisely prepare the socket in surgery. Patients who have weaker bone are treated with anti resorptive medication and a longer period on crutches after the surgery. We have reduced the rate of the complication of femoral neck fracture from 1-2% to 0.1% using this strategy.