Robotic system for cervical spine surgery

Abstract

In contemporary surgical clinical practice, spinal instability is often treated with mechanical stabilization techniques in order to protect the spinal cord and nerve roots. These techniques involve placing screws in defined regions of the vertebrae, typically the pedicle, where the strongest bone is found. The challenge for the surgeon is the accurate placement of screws for good mechanical purchase and to avoid damage to surrounding vital anatomical structures. This is especially critical in the cervical region, where the target bone mass is smaller and the spinal cord, nerve roots and vertebral arteries are all at risk. A robotic system enabling the surgeon to precisely place implants into the vertebrae should enhance safety and may potentially improve surgical results. We describe such a system, which consists of a compact robot positioned using a passive structure, an optical tracking system, a surgical input device and planning and navigational software. The implant trajectory in each vertebra is planned preoperatively, using fine-cut computerized tomography (CT) scans. During surgery, registration matching between the CT scan and the patient's anatomy is achieved using point to point registration, refined with a surface merge technique. Approximate robot positioning is done passively by the surgeon. Final precise instrument positioning is performed by the robot according to the planned trajectory through the target vertebra. Implants (screws) are then placed through the robot-guided working channel. Six cadaver experiments, consisting of placing transarticular (i.e. crossing the joints between the vertebrae) screws in the upper two vertebrae of the human cervical spine, were performed. Implant placement accuracy was comparable with that achieved using freehand image-guided techniques by an experienced surgeon. These results confirm the utility and applicability of the system. It is currently in redesign to improve accuracy and to render it compatible with on-line planning.