Plastic Surgery Research Council
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Presenter: Benjamin Levi, MD
Co-Authors: Peterson J; De La Rosa S; Okabare P; Cilwa K; Oluwatobi E; Morris M; Kozloff K; Cederna PS; Buchman SR; Wang SC
University of Michigan

Intro: Heterotopic Ossification (HO), or the abnormal formation of bone in soft tissue, occurs in over 60% of major burn injuries. Current diagnostic modalities for HO are inadequate to diagnose HO early enough to allow for intervention. In this study, we validate transcutaneous, in-vivo Raman spectroscopy for earlier transcutaneous diagnosis and characterization of HO than current gold standard MicroCT imaging in a mouse achilles tenotomy model which is enhanced by burn injury.

Methods: The left achilles tendon was divided at the midpoint in 14 mice. Following tenotomy, mice were split into burn and sham groups with exposure of 30% dorsal surface area to 60? or 30? water for 18 seconds respectively (n=7 per group). In-vivo, transcutaneous Raman spectroscopy, MicroCT and Near Infrared Spectroscopy (NIR) was performed at 5 days, 2 weeks and 3 months on the tenotomized and control leg. Following sacrifice, the samples were imaged on an ex-vivo Raman platform. Bone formation was verified with NIR, Micro CT and histology.

Results: Our Raman probe allowed non-invasive, transcutaneous evaluation of heterotopic bone formation 5 days post injury while MicroCT, did not detect HO at 2 weeks (Fig. 1). Significantly increased intensity of bone mineral signaling was found in the burn group compared to sham group at 5 days post injury, with the difference increasing over time by Raman (p<.05, Fig. 2). Ex-vivo Raman measurements showed significant differences in the amount of HO in the burn compared to sham groups and also showed differences in the spectra and physical makeup of new, ectopic bone compared to native cortical bone (p<.05). HO was verified by NIR and histology (Fig 3).

Conclusion: Burn injury increases the likelihood of developing HO when combined with an achilles tenotomy. Raman spectroscopy allowed for earlier diagnosis of HO than current gold standard MicroCT techniques in our in-vivo model. Changes in bone mineral and matrix composition of the new bone were also evidenced in the Raman spectra which could facilitate early identification of HO and accelerate therapy decisions for HO patients.

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