Metastatic lesions affecting bone are more common than primary bone tumours.

The typical tumours that spread to bone include:

• Breast
• Bronchus
• Renal
• Thyroid
• Prostate

75% cases will affect those over the age of 50

The commonest bone sites affected are:

• Vertebrae (usually thoracic)
• Proximal femur
• Ribs
• Sternum
• Pelvis
• Skull

Pathological fracture

Osteolytic lesions are the greatest risk for pathological fracture

The risk and load required to produce fracture varies according to bone site. Bones with lesions that occupy 50% or less will be prone to fracture under loading (Harrington). When 75% of the bone is affected the process of torsion about a bony fulcrum may produce a fracture.

The Mirel scoring system may be used to help determine the risk of fracture and is more systematic than the Harrington system described above.