Photoacoustic differentiation of cortical from cancellous bone in the lumbar vertebrae of an intact human cadaver to prevent bone breaches during spinal fusion surgeries

In spinal fusion surgeries, it is critical to maintain correct trajectories during the process of creating pedicle holes for screw insertion, in order to avoid accidental bone breaches and screw misplacement, which are characterized by screws placed within surrounding cortical bone rather than the cancellous core of the pedicle. One key difference between these two bone types is the greater porosity of the cancellous bone when compared to the more dense, more compact cortical bone. This work investigates the feasibility of using photoacoustic imaging to differentiate cortical from cancellous bone in the lumbar vertebrae of an intact human cadaver, with the ultimate goal of developing a novel photoacoustic surgical system to prevent breaches. Eleven pedicle cannulations were performed in the lumbar vertebrae of a human cadaver, including six holes in the cancellous core and five partial or complete breaches of surrounding cortical bone. Amplitude-based delay-and-sum (DAS), coherence-based short-lag spatial coherence (SLSC), and locally weighted SLSC (LW-SLSC) beamforming were used to characterize differences in the morphology of photoacoustic signals originating from cancellous and cortical bone. Statistically significant differences between the median of measured areas from cortical and cancellous bone measured 6.61 mm2 for -6 dB contours obtained with DAS beamforming and ranged from 2.89 mm2 to 42.13 mm2 for -10 dB and -15 dB contours obtained with DAS, SLSC, and LW-SLSC beamforming (p<0.001). In addition, coherence-based photoacoustic imaging enabled localization of the tip of the optical fiber that was inserted into each prepared pedicle hole. Therefore, both DAS and SLSC beamforming has the potential to synergystically detect the tip of surgical tools and differentiate between signals originating from cortical and cancellous bone. These results are promising for surgical guidance within the desired cancellous core of the pedicle and away from the surrounding cortical bone, in order to avoid costly and painful bone breaches during surgery. To read more click here