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

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Abstract

Study Design.

Prospective and randomized experimental study with anterior lumbar interbody fusion in a porcine model.

Objective.

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).

Summary of Background Data.

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.

Methods.

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. 18F 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.

Results.

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, R2 = 0.8275, was observed for intertrabecular volume/total volume and T2-values.

Conclusion.

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.

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