Radionuclide imaging after skeletal interventional procedures

Although nuclear medicine is often used as an adjunct to planning skeletal therapeutic interventions, its role in the assessment of these various interventional procedures, after the fact, is equally important. Skeletal therapeutic interventions studied with radionuclide imaging include bone grafts, the postoperative spine, and joint replacements. Vascularized bone grafts allow the successful reconstruction of large bone gaps. Early detection of vascular compromise permits prompt reevaluation of the vascular anastomosis so that potentially reversible causes of ischemia can be corrected. Radionuclide bone scintigraphy is a simple noninvasive method to evaluate the anastomotic patency of these grafts. Scintigraphically, vascular patency is characterized by normal or diffusely increased tracer uptake throughout the graft, whereas failure of the graft presents as photopenia. Bone scintigraphy, especially single photon emission computed tomography (SPECT), is of considerable value in the work-up of patients with persistent back pain after spinal surgery. Postoperatively, spinal fusion is characterized by diffusely increased uptake of radiotracer in the fused area. In contrast, focally increased uptake has been shown to be related to bony nonunion or pseudoarthroses. In patients who have undergone laminectomy, SPECT bone scintigraphy can localize the level of maximum instability and vertebral stress. The radionuclide evaluation of joint replacement complications, especially of hip and knee prostheses, has been extensively studied for nearly 2 decades. Bone scintigraphy is probably most useful when the images are normal. Although periprosthetic sites of increased uptake may be indicative of postoperative problems such as loosening or infection, they may also merely reflect postoperative changes. Dual tracer studies, focusing primarily on the diagnosis of the infected joint replacement, have consequently become the norm. Bone-gallium scintigraphy was the earliest dual tracer modality used, with an accuracy of 60% to 80%. The current radionuclide study of choice for diagnosing the infected prosthesis is labeled leukocyte-marrow imaging. Both leukocytes and colloid tracers accumulate in marrow, whereas only leukocytes accumulate in infection. This technique facilitates the discrimination of labeled leukocyte uptake in aberrant, but not abnormal, marrow from uptake in infection. The reported accuracy of this technique consistently exceeds 90%.