Paget’s disease of bone (PDB) is a chronic metabolic bone disorder characterized by bone thickening and deformity. The spine is the second most commonly affected site after the pelvis, with more than half of patients showing spinal involvement. The disease is usually polyostotic and involves multiple skeletal sites. In the spine, PDB can affect one or multiple segments. The most common site is the lumbar spine, with L4 and L5 being the most commonly involved segments.
PDB shows characteristic features on plain radiographs and CT of the spine that allow easy diagnosis . These features include expansion of the vertebral body with increase in the anteroposterior and lateral vertebral dimensions and slightly decreased or unchanged vertebral height (Fig. 90.1). The vertebral body is almost always involved in a diffuse fashion, together with a variable portion of the neural arch. Loss of the concavity of the vertebral bodies anteriorly as well as posteriorly is a common feature. Trabecular hypertrophy paralleling the vertebral endplates, combined with thickening of the endplates and the cortex, results in an increased density in the vertebral periphery and a relatively lucent centre in the vertebral body, which is likened to a “picture frame” on radiographs and CT. The initial lytic phase of PDB does not occur in the spine. Progression of the sclerotic phase leads to the “ivory vertebra” appearance.