Computer navigated surgery describes a revolutionary set of technologies which allow computerized imaging, analysis, projection, and programming to plan or execute surgery. It is a key component in modern surgery and robotic surgery. Computed assisted surgery is usually facilitated by a sequence of steps including 1. Image acquisition 2. Image analysis 3. Image simulation 4. Surgical navigation and optionally, 5. Robotic surgery. The most sophisticated systems have all these steps.
Image acquisition consists of using an imaging modality to enter the patient’s surgical area of interest (e.g. lumbar spine in spine surgery) into the computer’s database. The best images are usually from a computer tomography scan (CAT scan) but plain Xrays, MRI or Ultrasound have all been used. The images may be obtained preoperatively or, more accurately, intraoperatively and multiple modalities may be fused together to make a single database. The imaging may also include surgical instruments and critical markers, which will be integrated into the dataset to facilitate the further 3Dimensional simulation and surgical navigation steps.
In the second phase, the computer analyses the data to reconstruct a 3 dimensional digital dataset of the patient’s anatomy from the imaging. This dataset is a correctly scaled digital representation of the entire scanned area or volume, with correct distances and depths. This will often contain reference markers or instruments (like the “you are here” marker on a building map) to give the surgeon feedback of where the marker on the patient is found in the image. This is the basis on which all the planning and execution will be done.
In the Image simulation phase, the computer uses its 3D reconstruction of the patient’s anatomy to create visual representations, which the surgeon can view, manipulate and even interact with. These may highlight various parts of the anatomy and hide other parts, as decided by the surgeon. Hence, muscles and fat may be hidden to show only the bone, as in the case of spinal surgery. Also, several different views may be shown simultaneously e.g. cross-sectional views from the front, side, top or bottom, in addition to the entire 3 dimensional reconstruction. This allows a realistic view of the patient’s imaged area that would not be available to the naked eye, giving the surgeon “Xray vision”. These images are displayed in real time and hence the surgeon is able to use the computer representation to assess the inner depths of the patient virtually, before even making an incision to see the tissues for himself.
The navigation phase is a continuation of the simulation phase. Here, the surgeon can move an actual instrument near to the patient and see where the virtual projection of that instrument will be in relation to the inner structures of the patient. As the images can be updated real time, the computer provides a live virtual image of the patient and the surgeon’s instrument simultaneously as the surgeon moves the instrument. To enable this the computer is fitted with a camera that can track or “see” specially marked instruments, and include them in its 3D simulations of the patient. Hence the surgeon can use the simulation to accurately “navigate” to a region of interest, making smaller incisions and accurately placing the instrument or implant, even when he cannot see the actual tip of the instrument.
The final phase of computer navigation is that of robotic surgery. In this step, a surgical robot is used to accurately replicate a particular part of a surgery, such as the placement of a screw. Here, an implant is planned and placed in the simulation, and then the computer programming instructs the robot how to accurately and safely place an actual screw in that simulated position, in the real patient. The entire process is monitored by the surgical team, who also perform the remainder of the surgery, as per normal.
These techniques are particularly useful in regions of complex anatomy e.g. the spine, in circumstances where the anatomy is unusual, e.g. deformity surgery or revision surgery. The technique has been shown to increase the accuracy of placement of screws in the spine when compared to other non-navigated techniques. It also allows better planning of surgery, use of smaller incisions and decreases surgical errors.
Content written by Dr Kimani White & Dr Ashish Diwan