The Diagnosis of Osteoporosis: Identifying the patient at high risk of fracture

Definitions

In a 1993 consensus conference, osteoporosis was defined as a systemic skeletal disease characterized by low bone mass and micro-architectural deterioration of bone tissue with a resultant increase in fragility and risk of fracture. More recently the National Institutes of Health consensus conference modified this definition to reflect that bone strength is more than just bone density and introduced the concept of bone quality. They defined osteoporosis as follows: a skeletal disorder characterized by compromised bone strength predisposing a person to an increased risk of fracture. Bone strength reflects the integration of two main features: bone density and bone quality.

Probably, the only clinically applicable index of bone quality at present is a patients history of a fragility fracture. A fragility minimal trauma, such as a fall from a standing height or less, or occurs without identifiable trauma.

Given the absence of applicable measures of bone quality in practice, the diagnosis of osteoporosis tends to be made on the basis of low bone density. WHO definitions are used in interpreting BMD which are based on a comparison of a patients BMD with the mean for a normal young adult population of the same sex and race. The patient is assigned a T-score, which is the number of standard deviations above or below the mean BMD for normal young adults as follows:

Normal BMD is defined as a T-score between +2.5 and 1.0 (i.e., the patients BMD is between 2.5 standard deviations (SDs) above the young adult mean and one SD below the young adult mean). Osteopenia (low BMD) is associated with a T-score between 1.0 and 2.5, inclusive. Osteopenia is also a term used by radiologists to indicate that the bones on a plain X-ray film appear to be of decreased mineral content.

Osteoporosis is defined as a T-score lower than 2.5.

Severe osteoporosis describes patients whose T-score is below 2.5 and who also have suffered a fragility fracture.

Four Key Risk Factors for Fracture

After reviewing the literature and considering the effect of potential confounders, Osteoporosis Canada identified four key factors as predictors of fracture related to osteoporosis: low BMD, prior fragility fracture, age and family history of osteoporosis. Other factors that are commonly cited risk factors were not found to be consistent independent predictors of fracture risk, after taking into consideration age and/or BMD.

BMD

The techniques for measuring bone density may be divided into those that measure the central skeleton (spine, proximal femur, whole skeleton, etc.) and those that measure some part of the peripheral skeleton. Measurement of the central skeleton is most widely carried out using dual-energy X-ray absorptiometry (DXA). DXA bone measurement (with consideration of age) is the most effective way to estimate fracture risk in women

It is clear from epidemiology studies that age is a major risk factor for fracture. Because low BMD is also a major risk factor for fracture and BMD decreases with age, there must also be an age at which it is worthwhile to begin using BMD as a screening tool. Osteoporosis Canada has taken the position that BMD testing is appropriate for targeted case-finding among people under age 65 and for all women age 65 and older because of the high risk of osteoporosis and fracture after that age

Prior Fragility Fracture

Established osteoporosis may still be recognized on radiographs of the spine. However, because some two thirds of spinal fractures are not diagnosed clinically, one cannot rely on radiographs obtained to investigate back pain. Although there is some debate over what constitutes a vertebral fracture deformity, the most widely used criterion is derived from measurements of the vertical height of a vertebra at its anterior margin, centre (or midposition) and posterior margin.

A prior fragility fracture places a person at 1.5 to 9.5 fold increased risk for another one depending on the age at assessment, number of prior fractures and the site of the incident fracture For example the presence of a vertebral fracture increases the risk of a second vertebral fracture at least four-fold and 20% of those who experience one vertebral fracture will have a second vertebral fracture within one year. Vertebral fractures are also indicators of increased risk of fragility fractures at other sites, such as the hip.

Family History of Osteoporotic Fracture

This factor has been best studied with respect to hip fracture. One study identified a maternal history of hip fracture as a key risk factor for hip fracture in a population of elderly women. A history of hip fracture in a maternal grandmother also carries an increased risk of hip fracture Although most studies have focused on the index persons mother or other female family members, genetic influence on the risk of osteoporosis is multi-factorial, and one should not ignore a history of osteoporotic fracture in first- or second degree male relatives. It is now clear that fractures are common in men; therefore, although the recommendations focus on hip fractures in a patients mother or grandmother, other family members should be included during assessment.