ISSLS prize winner: positron emission tomography and magnetic resonance imaging for monitoring interbody fusion with equine bone protein extract, recombinant human bone morphogenetic protein-2, and autograft.

Prospective and randomized experimental study with anterior lumbar interbody fusion in a porcine model. To assess the early time-course of spinal fusion with equine bone protein extract (COLLOSS E), recombinant human bone morphogenetic protein-2 (rhBMP-2), and autograft using quantitative methods of positron emission tomography (PET)/computed tomography and magnetic resonance imaging (MRI). Different growth and differentiation factors are currently being used for inducing bone formation in spinal fusion. However, the mechanisms and time-course of bone formation using these graft substitutes remain less known. Eighteen female Danish landrace pigs underwent a 3-level anterior lumbar interbody fusion procedure from L3-L6. A PEEK cage, packed with COLLOSS E, rhBMP-2, or autograft, was randomly placed. Each group of 6 pigs was observed for 2, 4, or 8 weeks, respectively. F PET/computed tomography and MRI examinations were performed, and data were correlated with histomorphometry. PET data were analyzed using a Gjedde-Patlak plot. K-values from the plot correspond to the metabolic rate. T2-values were calculated by T2 mapping. rhBMP-2 presented the highest bone formation on histologic sections at 25.6% at 4 weeks after surgery. Eight weeks after surgery, autograft had the highest bone formation with 37.3%, which was significantly higher than rhBMP-2 at 30.5% (P < 0.05), and higher than COLLOSS E at 27.0% (P = 0.06). COLLOSS E and rhBMP-2 had significantly higher K-values than autograft (P < 0.05) at 2 weeks after surgery. There were no differences in K-values between COLLOSS E and autograft at 4 and 8 weeks. However, rhBMP-2 was significantly higher at 4 weeks and lower at 8 weeks than these 2 (P < 0.05). Linear correlation, R = 0.8275, was observed for intertrabecular volume/total volume and T2-values. PET and MRI are valid tools for monitoring the process of interbody fusion in vivo. Osteogenic mechanisms using COLLOSS E resembles that of autograft by the process of endochondral ossification. rhBMP-2 deposits osteoid directly on the collagen network.