Bone quality assessment using internal reference quantitative computed tomography for pre-operative planning on spinal surgery

Abstract

For spinal surgery, surgical planning remains a challenge for pedicle screw and intervertebral cage instrumentation, considering only the anatomical symmetry of instrumentation planning. However, low bone quality or osteoporotic condition in the surgical regions has been neglected, leading to post-surgical complications like screw loosening or cage subsidence. Limited studies have addressed the vertebral bone quality assessment from spinal degenerated patients using clinical computed tomography (CT) images. Proper bone quality assessment method through clinical CT to provide surgical instructions is still lacking. The study aims to develop an internal reference vertebral body bone quality assessment method that can be used as a pre-operative planning system for spinal surgery. The specific objectives were (1) to develop an internal reference quantitative computed tomography (QCT) assessment method to quantify the bone mineral density and estimate bone strength by using the clinical CT scans; (2) to study the correlation of vertebral bone quality profile with the prevalence of spinal degenerative changes; (3) to explore the bone quality of pedicle screw trajectory with the developed internal reference QCT-based bone quality assessment method. This study presents the development of a novel internal reference QCT-based vertebral bone quality assessment method. The method was validated by evaluating the developed system's accuracy with commercially available systems for bone mineral density (BMD) quantification and bone strength estimation. Further, the bone quality profiles of vertebral with and without degenerative changes were studied based on case controls. In addition, the distribution of localized BMD in degenerated vertebral subregions was investigated, such as the BMD of vertebral cortical endplate and its adjacent trabecular region. Lastly, the pedicle screw trajectory BMD and pullout strength was analyzed using the patient’s pre-operative CT image to justify the feasibility of trajectory optimization. The results showed the accuracy of the developed internal reference QCT-based bone quality assessment was equivalent to the predicate devices when perform the BMD measurement and bone strength estimation. The accuracy of BMD measurement interpreted as systematic difference compared with Philips Bone Mineral Content approach was 0.09 mg/cm3, and the accuracy of vertebral bone strength estimation interpreted as systematic difference was 3% when compared with a finite element solver, Abaqus. From the bone quality profile studies, patients with spinal degenerative changes have a less robust bone quality profile compared with non-degenerated patients. The feasibility analysis of using bone quality assessment to optimize pedicle screw trajectory showed significant improvements on both trajectory BMD and trajectory pullout strength. In conclusion, the vertebral bone quality profile associated with degenerative spinal changes is lower than patients without degenerative spinal changes. Using the internal reference quantitative computed tomography to perform vertebral bone quality assessment has reached equivalent accuracy for clinical application. We noticed that the degenerated vertebral body is more fragile and vulnerable than the average vertebral body. Besides, pedicle screw trajectory can be further optimized pre-operatively by referencing the trajectory BMD and trajectory strength. This evidence suggests that pre-operative vertebral bone quality assessment is essential to optimize the surgical outcomes for spinal degenerated patients.