Imaging of Musculoskeletal Disorders
Osteoporosis

The diagnosis of osteoporosis/osteopaenia is not made on the basis of plain X-ray or CT appearances, but if the bones appear to be low in density, then the diagnosis can be suspected.

For formal diagnosis of osteoporosis/osteopenia, duel-energy X-ray absorptiometry (DXA or DEXA) is required.

DXA scan

The lumbar spine and proximal femur are imaged using two X-ray beams of different X-ray energy levels. Soft tissues of the body absorb the low energy beam, and bone absorbs the high energy beam. Comparison of the amount of radiation absorbed by the two X-ray beams (absorptiometry) can be used to estimate bone density.

The estimated bone mineral density (BMD) is compared to a standardised young adult (YA) population and expressed as a statistical T-score. This T-score is plotted on a graph according to the age of the patient. Patients with a T-score <-1 have osteopenia. Patients with a T-score <-2.5 have osteoporosis.

A Z-score may also be expressed. This matches bone density against that of normal subjects of the same age and sex as the patient. A low Z-score should prompt investigations for an underlying cause of osteoporosis.

Insufficiency fractures

Osteoporosis results in a greatly increased risk of fractures, often referred to as 'insufficiency fractures'. Osteoporotic fractures are a type of pathological fracture – a fracture occurring in abnormal bone. Common sites include the wrist/forearm, femoral neck, vertebral bodies, and sacrum.

Vertebral body fractures

Below are some examples of insufficiency fractures of the vertebral bodies.

Sacral fractures

Insufficiency fractures of the sacrum are often undisplaced and are difficult to detect using X- rays. Even CT is limited in detection of these fractures.

For this reason, if a sacral fracture is suspected in a patient with osteoporosis, then an isotope bone scan may be performed.

For more examples of osteoporotic fractures see the introduction to trauma X-ray tutorial,the trauma X-ray lower limb gallery, and the trauma X-ray axial skeleton gallery.