Bone strength is determined by bone density and bone quality. Components of this are structural and material in nature. Structural properties include bone shape, size, and microarchitecture. Material properties include mineralization, collagen composition and damage accumulation.
Bone maintains its strength and quality by having a balance between bone resorption and formation. This is called remodeling. Old, damaged bone is resorbed and new bone is formed. Bone cells called osteoclasts remove the old structures and osteoblasts lay down the material for new bone formation. Osteoporosis develops when this balance is disrupted and there is more bone resorption than formation.
Bone mineral density testing is the standard way to measure bone integrity. This testing is performed using dual-energy x-ray absorptiometry (DEXA). It is the gold standard for diagnosing osteoporosis. The World Health Organization (WHO) has defined criteria for normal and abnormal results. The T score is utilized and describes the number of standard deviations (SD) in which a person’s results exceeds (positive score) or falls below (negative score) the mean of a young adult group of the same sex.
A diagnosis of Osteoporosis is given when the value falls 2.5 standard deviations (T score of -2.5) or more below the mean. Osteopenia or low bone density occurs when the T score is -1.0 to -2.5. If the score is greater than -1.0, the bones are considered to be of normal density. This T score is based on the mean value of a young adult reference population. Sometimes it is desirable to compare the individual to an aged matched control. The Z score is utilized in this situation allowing for a more age appropriate comparison since anyone can develop these problems.
These ranges were developed to identify individuals who are at increased risk of fractures. The goal of early diagnosis and prevention is to minimize the incidence of fracture and other morbidity as they can have life threatening and life altering consequences.
I hope this article has provided you with information that will help you make wise choices, so you may:
Live healthy, live well and live long!
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