DYNAMIC CONTRAST-ENHANCED MR-IMAGING ASSESSMENT OF VASCULARIZED FREE FIBULAR GRAFTS

Magnetic resonance (MR) imaging may be a noninvasive method for assess ing perfusion of vascularized bone grafts placed for treatment of avas cular necrosis. one proximal femur of seven beagles was devascularized , with insertion of a vascularized fibular graft. MR imaging at 1 week (seven dogs) and 6 weeks (five dogs) after surgery included pre- and postcontrast spin-echo sequences. unenhanced two-dimensional time-of-f light (TOF) vascular imaging, and dynamic gradient-echo imaging during infusion of gadolinium. Relative signal intensity values of selected regions obtained from the dynamic gradient-echo images were plotted as percent enhancement versus time. In the operated hip. MR imaging did not show enhancement in six of seven femoral heads and greater trochan ters at 1 week after surgery. with similar results after 6 weeks. MR i maging of fibular grafts 6 weeks after surgery showed an initial rapid increase in enhancement and a subsequent slower increase in five of f ive dogs, although no enhancement was wen in six of seven dogs at 1 we ek. These findings contrasted with a rapid initial increase in enhance ment followed by slow decline in non-operated hips. Two-dimensional TO F imaging did not show the vascular pedicle of the graft in any dog. F indings of radionuclide bone scanning performed 1 week after surgery w ere consistent with devascularization of the operated femur and fibula r graft. However, tetracycline distribution and histologic findings co nfirmed the viability of five of five grafts within the devascularized femurs 6 weeks after surgery. Thus, dynamic contrast-enhanced MR imag ing at 6 weeks after surgery is valuable for assessing vascular bone g raft perfusion, while similar imaging at 1 week may suggest Otherwise.