01/3 Endoscopic application systems

		Schematic overview of the proposed endoscopic application system

Surgical procedures on lumbar and thoracic vertebrae are quite common following trauma or for degenerative herniation of disc. To treat these disorders, it is argued, endoscope based minimally invasive surgeries are better, compared to their invasive counterparts, due to decreased access morbidity and cost-effectiveness.On the contrary, 2D visualisation of operative site, minimal accessibility and reduced dexterity, in minimally invasive surgeries, increase the possibility of injuring vasculature, spinal cord with its emanating nerves and inaccurate positioning of the prosthetic devices. Opting for image guided navigation during these surgeries will counter the inadequacies and improve safety and accuracy to a significant degree. Computer assisted navigation during posterior spine surgeries has proven to increase safety and helps in positioning of prosthetic devices with significant accuracy.

Computer assisted navigation has been tried during minimally invasive surgeries on anterior parts of thoracic/lumbar vertebrae. Main difficulty is in rigidly fixing the dynamic reference base (DRB) to these vertebrae, which has to be done with a long stylus allowing it to protrude out from the opposite abdominal wall or it is fixed to the iliac crest and stringent immobilisation of the patient is ensured. These methods are susceptible to instability and hence inaccurate. Therefore, there is a requirement for a new kind of tracking system to provide effective navigation during these surgeries. Availability of high resolution, magnified and relatively noise-free endoscopic images in a small work space opens up the possibility of using endoscope as a tracking tool. Instead of optoelectronically trackable DRB an artificial fiducial marker is attached to the vertebra, to be operated, and markers position and orientation is ascertained by means of image analysis. The endoscope is attached with another optoelectronically trackable DRB to establish a global co-ordinate system for instrument overlay.