A bone scan is a test that produces images of the bone to detect changes in the bone’s metabolism (natural processes that create and use energy).

Bones provide support for the body, store important minerals and contain bone marrow, which manufactures red blood cells. Bones break down and regrow over time as a normal part of body function, a process called bone turnover. Bone turnover can also occur as a result of injury or disease. A bone scan identifies areas of normal and abnormal bone turnover.

A bone scan may be performed on the entire body or just part of it. It is sometimes used instead of an x-ray because it can identify problems an x–ray would not detect. It can also detect some problems earlier than an x–ray.

Bone scans are a type of nuclear medicine (radionuclide imaging), meaning they involve the use of tiny amounts of radioactive materials called tracers (radionuclides). After they are placed in the body, tracers emit waves of radiation. The waves are detected by a device called a gamma camera that picks up radioactivity. Images produced by the camera are analyzed by trained medical professionals.

Depending on what condition the physician is testing for, images may be taken immediately after injection of the radioactive tracer or taken after few hours.

Bone scans differ from x–rays in that x–rays pass radiation through the body to produce pictures on film placed on the other side of the body. A bone scan also differs from a bone mineral density test (DEXA scan), which uses certain low-dose x–rays to test for osteoporosis.

There are numerous injuries, conditions and diseases that a bone scan may identify. These include:

• Fractures. A bone scan may be used to diagnose small or hidden fractures that do not appear on a standard x–ray.
  

  

• Cancer. The test is sometimes used to diagnose cancer in the bone or determine whether a cancer that originated elsewhere in the body, such as the prostate, breast, lung or kidney, has spread (metastasized) to the bone.
  
  
• Degenerative diseases of the bones, such as arthritis. Bone scans can also identify joints that are at potential risk of developing early osteoarthritis after trauma. Occasionally a torn anterior cruciate ligament in the knee may lead to early post-traumatic osteoarthritis that a bone scan may detect earlier than an x-ray.

• Paget’s disease. A disease in which bone breaks down more quickly than normal and, when it grows back, is softer than normal and not as resilient.
  
  
• Osteomyelitis. An acute or chronic bone infection, usually caused by bacteria.
  
  
• Osteomalacia. A condition involving softening of the bones caused by vitamin D deficiency. In children, it is called rickets.
  
  
• Fibrous dysplasia. A disease of the bone in which the bone’s outer layers become thin. The inner bone marrow is replaced by a gritty, fibrous tissue containing sharp, needle–like fragments of bone.
  
  
• Avascular necrosis (osteonecrosis). Disease resulting from the temporary or permanent loss of blood to the bones.
  
  
• Shin splints. This common athletic injury can often be diagnosed during a physical examination. Sometimes a bone scan or other imaging tests are ordered to distinguish shin splints from a stress fracture in the tibia (shinbone). In shin splints the tracer does not accumulate in a localized area, but typically accumulates along the length of the tibia. In stress fractures, the substance accumulates around the area of the fracture.
  
  
• Unexplained pain. A scan may be performed to help identify the cause or location of unexplained bone pain, such as lower back pain.

Bone scans are sometimes used in cases of suspected child abuse because the test can detect patterns of repeated trauma.