Diffuse reflectance spectroscopy accurately identifies the pre-cortical zone to avoid impending pedicle screw breach in spinal fixation surgery

Abstract

Pedicle screw placement accuracy during spinal fixation surgery varies greatly and severe misplacement has been reported in 1-6.5 % of screws. Diffuse reflectance (DR) spectroscopy has previously been shown to reliably discriminate between tissues in the human body. We postulate that it could be used to discriminate between cancellous and cortical bone. Therefore, the purpose of this study is to validate DR spectroscopy as a warning system to detect impending pedicle screw breach in a cadaveric surgical setting using typical clinical breach scenarios. DR spectroscopy was incorporated at the tip of an integrated pedicle screw and screw driver used for tissue probing during pedicle screw insertions on six cadavers. Measurements were collected in the wavelength range of 400-1600 nm and each insertion was planned to result in a breach. Measurements were labelled as cancellous, cortical or representing a pre-cortical zone (PCZ) in between, based on information from cone beam computed tomographies at corresponding positions. In addition, DR spectroscopy data was recorded after breach. Four typical pedicle breach types were performed, and a total of 45 pedicle breaches were recorded. For each breach direction, the technology was able to detect the transition of the screw tip from the cancellous bone to the PCZ (P < 0.001), to cortical bone (P < 0.001), and to a subsequent breach (P < 0.001). Using support vector machine (SVM) classification, breach could reliably be detected with a sensitivity of 98.3 % [94.3-100 %] and a specificity of 97.7 % [91.0-100 %]. We conclude that DR spectroscopy reliably identifies the area of transition from cancellous to cortical bone in typical breach scenarios and can warn the surgeon of impending pedicle breach, thereby resulting in safer spinal fixation surgeries.

Diffuse reflectance spectroscopy for breach detection during pedicle screw placement: a first in vivo investigation in a porcine model

“…1). This finding agrees with previous publications on human cadavers [17,18]. However, a high variability of blood content and fat fraction in cancellous bone and PCZ regions within the vertebra was found as represented by the error bars in Fig.…”

“…3). This finding also further validates previous Swamy et al BioMed Eng OnLine (2020) 19:47 cadaveric studies which investigated the use of intraoperative fat fraction measurements to detect breaches during pedicle screw placement procedures [17,18,25]. The stable nature of the fat fraction signal during continuous DRS measurement within the vertebral body, 70 min after the time of cardiac arrest, indicates the relative independence of fat and fat fraction measurements as compared to blood content measurements.…”

“…Tissue labeling of DRS measurements were performed by a trained physician, blinded to the DRS spectral readings, based on anatomical position of the probe on the CBCT verification scans. Anatomical regions of interest were defined as cancellous bone, cortical bone, pre-cortical zone (PCZ) and breach based on experience from a previous study [18]. PCZ was defined as the distance within 3 mm from cortical bone boundary.…”

“…Real-time monitoring of tissue characteristics using diffuse reflectance spectroscopy (DRS) at the tip of an instrument may offer a new possibility for intraoperative guidance. The technology can be used to determine physiological parameters such as fat and water content and fat fraction, within the tissues ahead of an instrument and has previously been investigated for detection of breaches during pedicle screw placement [17,18]. Using a custom-built screw probe with integrated optical fibers to sample fat fraction within vertebrae, the technology could accurately predict the transition from cancellous to cortical bone with high sensitivity and specificity [18].…”

“…The technology can be used to determine physiological parameters such as fat and water content and fat fraction, within the tissues ahead of an instrument and has previously been investigated for detection of breaches during pedicle screw placement [17,18]. Using a custom-built screw probe with integrated optical fibers to sample fat fraction within vertebrae, the technology could accurately predict the transition from cancellous to cortical bone with high sensitivity and specificity [18]. However, these studies were all performed ex vivo and the possible influence of blood at the tip of the probe could not be studied.…”