BONE DENSITOMETRY ( DEXA SCAN) Dr Malith Kumarasinghe MBBS (Colombo)

OSTEOPOROSIS Osteoporosis is the most common metabolic bone disorder. It has been defined by the National Institutes of Health as an age-related disorder characterized by decreased bone mass and increased susceptibility to fractures in the absence of other recognizable causes of bone loss.

OSTEOPOROSIS Risk factors may be superimposed upon either involutional or secondary osteoporosis, including smoking, alcohol, poor diet, lack of exercise, an early menopause, strong family history and small frame.

OSTEOPOROSIS The normal rate of bone loss is 2% per year, hence 20-40% of the female bone mass is already lost by the age of 65 years of age, beginning before the menopause and accelerating afterwards

OSTEOPOROSIS Bone mass is the major determinant of bone strength that can be measured by non-invasive techniques, and accounts for 75-85% of this parameter

OSTEOPOROSIS Bone densitometry is clinically indicated for the detection and assessment of osteoporosis and for the evaluation and monitoring of several diseases and therapies. These include: 1. The detection of osteoporosis and assessment of its severity. 2. Evaluation of perimenopausal women for the initiation of estrogen therapy. 3. Evaluation of patients with metabolic diseases that affect the skeleton. 4. Monitoring of treatment and evaluation of disease course. In addition it may be useful as an epidemiological tool and possibly in the future for screening American Society of Bone and Mineral Research

Osteoporosis Measurement  Plain film, Subjective, Radiogrammetry, Osteogram  SPA  DPA  DEXA  QCT  US  MRI

DEXA Because photons of different energy are differentially attenuated by bone and soft-tissues, by measuring the percentage of each transmitted beam and then applying simple simultaneous equations, the absorption by bone alone and hence bone density can be calculated. This measurement is not a true density but rather an areal density, represented in gms/cm 2

DEXA DEXA has very high accuracy (the difference in the measurement from a known standard)

DEXA DXA is at present the most precise measurement of BMD

DEXA Interpretation

Bone Densitometry DEXA spine check list  Note the age, sex, ethnicity and weight  Does this match the reference ranges?  Is the bottom of L4 roughly at the level of the iliac crests  Are there any ribs on L1  Scoliosis  Are the vertebrae correctly divided  Anything in the soft tissue

DEXA, what makes a good scan?  5-15 Lines of Iliac Crest. I recommend 1/2 of L5.  5-10 Lines of T12.  2 cm of tissue on both sides of the spine.  Spine should be straight.  No metal in spine.

Common problems with spine scans.  Spine isn’t straight.  Scan starts in sacrum.  Scan stops too soon.  Wrong scan mode.  Scan doesn’t include L5.

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