MRI EVALUATION OF FUSION MASS INCORPORATION AFTER ANTERIOR CERVICAL BONY FUSIONS - PRELIMINARY FINDINGS

While Modic3 has described certain MRI changes in bone grafts in patients after anterior cervical discectomy and fusion (ACF), no study has evaluated specific MRI signal changes in the fusion mass prospectively and longitudinally. The goal of the present study was to prospectively evaluate MRI changes in ACF grafts in a longitudinal fashion. Twenty-seven MRIs were included in the evaluation of seven postoperative patients. MRIs were obtained in a 1.5 tesla GE imager immediately postoperatively, and at 1, 3, and 6 months in most patients. All patients received at least three sequential MRIs. Two patients had greater than one level fused. T1 and T2 images were evaluated in all patients at each available interval. GRASS images were not found to be helpful secondary to a prohibitive amount of noise. For single level fusion masses, T1 images showed a very intense homogeneous graft signal in the immediate postoperative period which decreased slightly at 1 month. At 3 months the signal intensity of the graft was similar to the 1 month image, but was slightly less homogeneous. At 6 months, the T1 signal had greatly decreased in much of the graft. Immediate postoperative specimens showed heterogeneously high signal on T2 images which increased at 1 month in the whole graft, and then seemed to increase at the endplates while decreasing in the graft at 3 months. At 6 months the graft was becoming difficult to delineate on T2 images in many specimens. The two and three level fusions had a more heterogeneous image progression without clear evidence of solid fusion at 6 months. One patient with, a C3-4, C4-5, C5-6 fusion still showed heterogeneous intensity of both T1 and T2 signals at all levels 2 years postoperatively while remaining asymptomatic. This study documents specific progression of time-related signal changes in bone grafts after ACF. The identification of signals predictive of graft failure will require more prefailure MRIs of grafts which ultimately go on to pseudarthrosis. Multiple level fusions, known to have a lower fusion rate, demonstrate signal patterns dissimilar to single level fashions.