The role of bone imaging in orthopedic practice

The bone scan

Bone imaging continues to be the second greatest-volume nuclear imaging procedure, offering the advantage of total body examination, low cost, and high sensitivity. Its power rests in the physiological uptake and pathophysiologic behavior of 99m technetium (99m-Tc) diphosphonates. The diagnostic utility, sensitivity, specificity, and predictive value of 99m-Tc bone imaging for benign conditions and tumors was established when only planar imaging was available. Currently, nearly all bone scans are performed as a planar study (whole-body, 3-phase, or regional), with the radiologist often adding single-photon emission computed tomography (SPECT) imaging. Here we review many current indications for planar bone imaging, highlighting indications in which the planar data are often diagnostically sufficient, although diagnosis may be enhanced by SPECT. (18)F sodium fluoride positron emission tomography (PET) is also re-emerging as a bone agent, and had been considered interchangeable with 99m-Tc diphosphonates in the past. In addition to SPECT, new imaging modalities, including (18)F fluorodeoxyglucose, PET/CT, CT, magnetic resonance, and SPECT/CT, have been developed and can aid in evaluating benign and malignant bone disease. Because (18)F fluorodeoxyglucose is taken up by tumor cells and Tc diphosphonates are taken up in osteoblastic activity or osteoblastic healing reaction, both modalities are complementary. CT and magnetic resonance may supplement, but do not replace, bone imaging, which often detects pathology before anatomic changes are appreciated. We also stress the importance of dose reduction by reducing the dose of 99m-Tc diphosphonates and avoiding unnecessary CT acquisitions. In addition, we describe an approach to image interpretation that emphasizes communication with referring colleagues and correlation with appropriate history to significantly improve our impact on patient care.

When to use bone scintigraphy. It can reveal things other studies cannot

Despite advances in nuclear medicine, bone scintigraphy remains an important imaging technique. It is sensitive in detecting stress fractures and bone metastases and can assess suspected injury that is difficult to see on plain films (e.g., rib fracture). Scintigraphy is useful in evaluating new symptoms, response to therapy, and prognosis in patients with known malignant tumor. In patients with low back pain, the technique can determine the age of fractures to help identify osteoporosis and can uncover other causes of the pain (e.g., spondylolysis, arthritis). When Paget's disease is suggested by unexplained bone pain or an elevated serum alkaline phosphatase level, bone scintigraphy is a useful screening test. Combined with other appropriate nuclear medicine studies, it helps in early identification and localization of osteomyelitis. Scintigraphic scans can provide a general indicator of malignant versus benign disease (according to the amount of lesion activity seen) and may produce characteristic findings in certain primary tumors (e.g., osteoid osteoma) that are difficult to evaluate with other methods.