OP is a systemic skeletal disease characterized by low bone mass, caused by an imbalance between bone resorption and bone formation, and microarchitectural deterioration of bone tissue, with a consequent increase in bone fragility.

The WHO definition of OP is a t-score (measured using DXA scan) of ≥2.5 SDs below the mean BMD value for young, healthy, white women (or t-score of ≤-2.5).¹ Patients who have already experienced ≥1 fracture are considered to have severe or “established” OP. Osteopenia is defined as a t-score between -1 and -2.5.² The WHO diagnostic classification should not be applied to premenopausal women, men younger than 50 years, or children. Instead of a t-score, the ISCD recommends using ethnic or race-adjusted z-scores, with z-scores of ≤-2.0 defined as either “low bone mineral density for chronological age” or “below the expected range for age” and those ≥-2.0 being “within the expected range for age.”³

Risk factors for OP include advanced age (>50 years); female gender; Caucasian race; positive family history; smoking; immobilization; calcium deficiency; history of prior fractures; decreased estrogen, weight (<127 lbs), or BMI; alcohol use; and smoking.² Secondary causes of OP include disuse, hyperthyroidism, steroids, and heparin. Muscle pull is more important than weight bearing in disuse OP prevention.⁴