Osteoporosis is the loss of trabeculae from the bone. 

It is measured by many modalities but the standard test is still DEXA (dual emission Xray absorptiometry). It is reported as a comparison to young adult peers of the same sex. if it is less than 2.5 standard deviations below the standard comparison, the patient is classified as osteoporotic. Its screening, prevention and treatment are very important topics.

Indications to screen for it are:
1) Loss of height in a person
2) Vertebral fracture secondary to trivial trauma, or rib fracture or wrist fracture
3)Prolonged steroid usage
4) Post-menopausal female

Prevention is by exercise, calcium with vitamin D or estrogen replacement in post-menopausal females. Alendronate (Fosamax) is also used for this in 5mg/day dosage.

Treatment: Fosamax 10 mg and Risedronate (Actonel) are the only two drugs approved for treatment.

Osteomalacia on the other hand is loss of mineral without loss of the trabeculae on which the mineral sits. It occurs due to Vitamin D deficiency or presence of an inhibitor of its metabolism - Anti-epileptics are notorious for this.