Virtual and Augmented Reality in Spine Surgery

Introduction of Technology

The utilization of surgical intelligence technologies has evolved since the inception of medicine. Epstein et al. pioneered the use of intraoperative ultrasound for the resection of intramedullary tumors. Ultrasound remains an invaluable aid during the resection of spinal cord tumors. By visualizing the echogenic signal of intramedullary tumors, the surgeon can evaluate the cranial and caudal extension of the tumor and assess the completeness of the resection. Advances in magnetic resonance imaging, such as diffusion tensor imaging, permit the surgeon to appreciate the relationship of the corticospinal tracts to intramedullary tumors. When the midline is distorted by an expansile mass, an understanding of the position of the corticospinal tracts can be helpful during surgical resection and deciding placement of the initial myelotomy.

While adoption of image-guided surgery for cranial tumors was advocated by Kelly as early as 1990, image-guided surgery for spinal tumors has required further refinement and advances in technology. The application of an automated elastic registration algorithm allows for co-registration of intraoperative CT and preoperative MRI ( Fig. 13.1 ). This technology has been crucial in overcoming differences in spine curvature between pre- and intraoperative imaging, permitting the use of MRI to guide tumor resection. Integration of the MRI-based navigation into the operative microscope represents an application of augmented reality in spinal oncologic surgery. The tumor’s borders are outlined and superimposed on the surgeon’s view of the spinal cord. This technology aids the surgeon when the tumor’s borders are indistinct, helps assess completeness of resection, and, when integrated with diffusion tensor imaging, can help preserve corticospinal tracts.

While (3D) tumor overlays integrated into the operative microscope view of the patient represent an application of augmented reality, 3D multimodal images viewed on a workstation or using a headset (Hololens, Microsoft) represent an application of virtual reality ( Figs. 13.2 and 13.3 ). Multiple layers, including spinal cord, bone, and soft tissue, are constructed using CT and MRI images and subsequently fused using a virtual reality workstation (Surgical Theater, Mayfield, OH).

Surgical Treatment for Spinal Pathology

Clinical Studies

Clinical Presentation

A 31-year-old gentleman presented with an 8-month history of declining bowel, bladder, and sexual function. He more recently developed low back pain, a right foot drop, and numbness of the right buttocks, shin, and foot. He was unable to bear weight on the right leg, resulting in an antalgic gait. The pain was worse when lying down and with Valsalva. On examination he had no movement on right dorsiflexion and plantarflexion, brisk right patellar and Achilles reflexes, and decreased sensation on the dorsum of the right foot.

Preoperative Imaging

An MRI of the lumbar spine was obtained, which demonstrated an intradural intramedullary enhancing expansile mass within the conus and proximal cauda equina. The mass did not have a cystic component and MRI of the rest of the neural axis did not reveal any further lesions ( Fig. 13.4 ).

Surgical Plan and Intraoperative Imaging

A T11–L1 laminoplasty and microsurgical resection of the intradural intramedullary spinal mass was planned. The patient was positioned prone on a Jackson table. Using two Steinmann pins percutaneously placed into the right iliac crest, a stereotactic navigation reference array was affixed to the patient. An intraoperative CT scan (Airo, BrainLab, Munich) was obtained for computer assisted intraoperative navigation. The (prone) intraoperative CT scan was fused with the (supine) preoperative MRI using an elastic registration algorithm to account for differences in the curvature of the spine ( Fig. 13.5 ). An intraoperative 3D visualization system (Surgical Theater, Mayfield, OH) was integrated with the neuronavigation ( Figs. 13.6 and 13.7 ). The T11–L1 levels were localized and a 3-inch incision was made. A decompressive osteoplastic laminectomy of T11–L1 was performed. After the thecal sac was exposed, ultrasound was used to define the cranial and caudal extent of the tumor and the dura was subsequently opened. The cephalad and caudal ends of the intramedullary mass were fully exposed. Stereotactic neuronavigation with microscope integration confirmed the cranial and caudal extent of the tumor and accurately correlated with intraoperative ultrasound. A myelotomy was performed, and the mass was entered. The mass was densely adherent to the underlying neural tissue and the tumor was cyto-reduced using ultrasonic aspiration. Gross total resection was achieved. The dura was closed and reconstruction of the T11–L1 osteoplastic laminectomy was performed.