Arthroscopic Knee Surgery and Virtual Reality

Arthroscopic knee surgery is a form of Minimal Access Surgery (MAS) in which instruments are inserted into the knee through small incisions, often to repair the anterior cruciate ligament (ACL). A tube only 4 mm in diameter, containing a system of lenses, a small video camera, and a light source, is inserted into one incision in the knee. The light is beamed down the tube through optical fibers, and the lenses focus the image up the tube to the camera. A separate incision is made to insert instruments for inspection, grasping, and cutting. By creating only small incisions, the amount of recovery time for the patient is greatly reduced. With an experienced surgeon, arthroscopy is safe and effective, but training new surgeons is both difficult and expensive with conventional methods. This is where virtual reality comes in.

Until recently, to learn arthroscopy, trainees could only learn with cadavers or mechanical models, by observing the surgery, or by performing supervised operations. Real cadavers are difficult to come by, expensive to store, and often don't truly represent the features of a living body. And there are only a limited range of procedures that can be practiced upon artificial models. Observing and being supervised can also be helpful, but it seems that the most sensible method of learning is using a "virtual cadaver." A virtual cadaver is more cost effective, since there is no need to buy and store real cadavers, and a large amount of time is saved by not having to set up the specimen for the surgery. The virtual cadavers also allow for repeated examination and dissection of organs, are easy to "store," and are able to represent any segment of the population. In addition, they are able to reproduce any pathology on demand, and the trainee can receive automatic appraisal for any actions performed.

Because a virtual cadaver is capable of repeated dissections, it is a great tool for practicing exercises such as navigating around the knee, identifying significant landmarks, and rehearsing standard inspection routes. It is also useful in improving the necessary skills for arthroscopy. Through practice, the trainees are able to work on triangulating, which is determining the position of the arthroscope and another instrument in relation to each other in three dimensions while viewing a two-dimensional screen. Using virtual reality, they are also able to better relate the arthroscope view to their mental model of the knee, and improve their ability to manipulate instruments within close confines.

The systems themselves consists of either an instrumented glove or an input device to signify the instrument being used, and a monitor on which the images are displayed. It is possible that a stereoscopic head-mounted display might replace the monitor sometime soon, but at the moment it does not provide enough clarity over a wide enough field to reproduce a surgeon's normal working condition. By producing representations of three-dimensional environments on the monitor, it acts as a direct substitute for the usual video camera image without much loss in operational realism. Because some bending and flexing of the knee is necessary during an arthroscopy, in a virtual reality simulation an artificial knee is used to provide realistic forces when manipulated. The inside of the knee is all modeled in virtual reality, so the artificial knee is hollow, but in order to get an accurate simulation an electromechanical tracking device is placed just above the knee to detect movement and enhance realism. For collision detection, an audio cue is given when a surface is hit, and algorithms are being worked on to improve upon the current voxel-based detector. The virtual reality world also attempts to mirror the interaction of the surgical instruments by including such factors as gravity and blood flow in the simulation. In addition, the images are enhanced with video footage, which allows realistic views to be called up at any time depending on the position of the arthroscope. The computer that usually runs this software is an SGI RealityEngine, which is 5000 times faster than a regular 486-based personal computer. In order to create the illusion of reality that the program is attempting to do, that kind of speed is necessary to keep the image smooth and believable.

Arthroscopic knee surgery is a large market, especially in the United States where 120,000 arthroscopies are performed each year. Conventional methods are not cost-efficient, nor are they efficient enough to fully train new surgeons for this difficult surgery. However, with new progress in technology happening every day, it is only a short time before virtual reality is used to alleviate these problems.

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