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.

The research article presents an experimental study aimed at monitoring spinal fusion using three different substances – equine bone protein extract (COLLOSS E), recombinant human bone morphogenetic protein-2 (rhBMP-2), and autograft. The study employed imaging methods such as positron emission tomography (PET) and magnetic resonance imaging (MRI) to monitor the process. The results indicate that rhBMP-2 showed the highest bone formation 4 weeks after surgery, but autograft yielded greater bone formation after 8 weeks.

Objective and Background

• The objective of the study was to observe the early stages of spinal fusion using three different substances, namely equine bone protein extract (COLLOSS E), recombinant human bone morphogenetic protein-2 (rhBMP-2), and autograft. The process was monitored using positron emission tomography (PET) and magnetic resonance imaging (MRI).
• The background of the study is rooted in the fact that various growth and differentiation factors are used to induce bone formation in spinal fusion. However, the mechanisms and timeline of bone formation using these substitutes were not well-known.

Methods

• The experiment was conducted on eighteen female Danish landrace pigs that underwent a 3-level anterior lumbar interbody fusion procedure.
• Each group of 6 pigs was observed for variable periods – 2, 4, or 8 weeks. During the observation period, PET and MRI examinations were performed and the obtained data were compared with histomorphometry.
• The metabolic rate was identified using K-values from a Gjedde-Patlak plot, and T2 values were calculated for T2 mapping.

Results

• After 4 weeks, rhBMP-2 showed the highest bone formation. However, after 8 weeks, autograft had the highest bone formation, greater than both rhBMP-2 and COLLOSS E.
• COLLOSS E and rhBMP-2 had notably higher K-values than autograft 2 weeks after surgery. There were negligible differences in K-values between COLLOSS E and autograft at 4 and 8 weeks but rhBMP-2’s K-value was higher at 4 weeks and lower at 8 weeks.
• A strong linear correlation was observed between the intertrabecular volume/total volume and T2-values, indicating the accuracy of using these parameters for assessment.

Conclusions

• The study concluded that PET and MRI can be effectively used to monitor the process of interbody fusion in real-time.
• The osteogenic mechanisms using COLLOSS E were found to resemble that of autograft through the process of endochondral ossification. On the other hand, rhBMP-2 deposited osteoid directly on the collagen network.