RADIONUCLIDE IMAGING AFTER SKELETAL INTERVENTIONAL PROCEDURES

Although nuclear medicine is often used as an adjunct to planning skel etal therapeutic interventions, its role in the assessment of these va rious 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 reeva luation of the vascular anastomosis so that potentially reversible cau ses 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 norma l or diffusely increased tracer uptake throughout the graft, whereas f ailure of the graft presents as photopenia. Bone scintigraphy, especia lly single photon emission computed tomography (SPECT), is of consider able value in the work-up of patients with persistent back pain after spinal surgery. Postoperatively, spinal fusion is characterized by dif fusely increased uptake of radiotracer in the fused area. In contrast, focally increased uptake has been shown to be related to bony nonunio n or pseudoarthroses. In patients who have undergone laminectomy, SPEC T bone scintigraphy can localize the level of maximum instability and vertebral stress. The radionuclide evaluation of joint replacement com plications, especially of hip and knee prostheses, has been extensivel y studied for nearly 2 decades. Bone scintigraphy is probably most use ful when the images are normal. Although periprosthetic sites of incre ased uptake may be indicative of postoperative problems such as loosen ing or infection, they may also merely reflect postoperative changes. Dual tracer studies, focusing primarily on the diagnosis of the infect ed joint replacement, have consequently become the norm. Bone-gallium scintigraphy was the earliest dual tracer modality used, with an accur acy of 60% to 80%. The current radionuclide study of choice for diagno sing the infected prosthesis is labeled leukocyte-marrow imaging. Both leukocytes and colloid tracers accumulate in marrow, whereas only leu kocytes accumulate in infection. This technique facilitates the discri mination of labeled leukocyte uptake in aberrant, but not abnormal, ma rrow from uptake in infection. The reported accuracy of this technique consistently exceeds 90%. Copyright (C) 1995 by W.B. Saunders Company