Someday, simulators such as this may largely replace cadavers for certain procedures.


Published 5/1/2008
Peter Pollack

Knee simulator project moves from back room to main hall

Virtual knee trainer shows progress; validation studies beginning

A year ago, at the 2007 AAOS Annual Meeting, the Virtual Reality Arthroscopic Knee Surgery Simulator Project was tucked away in a private room. But in San Francisco in March 2008, the simulator was given a prominent position in the AAOS Resource Center, where any passerby could stop, watch, and try it out.

The simulator attempts to transition orthopaedic training away from the long-standing custom of using cadavers and into the computer age. The virtual reality system allows residents to rehearse a particular technique over and over until they achieve a perfect score. They can then progress to a new level of difficulty.

The project, designed in consultation with the AAOS, is being built by Touch of Life Technologies (ToLTech), which also developed the Visible Human Project®, producing detailed, three-dimensional computer models of normal male and female bodies by sectioning human bodies into slices as small as 0.33 mm across.

For the knee simulator, a normal human knee was sectioned into 0.1 mm intervals, allowing for a series of highly accurate measurements. The computer model based on those measurements allows a virtual knee to be displayed on a computer screen, similar to the output of an arthroscope.

Beneath the monitor is a physical mock-up of a human knee, along with a pair of surgical “tools.” Tiny motors in the tools are synchronized to the simulated knee in order to provide an instant tactile response to the user: maneuver the probe to a ligament on the display, and the probe will respond as though it was touching a real ligament.

A more realistic feel—and a mentor
Since 2007, the development team has refined its prototype with a series of internal upgrades for improved stability and a better user experience. In addition, several wish-list items have been added based on feedback from surgeons who used the simulator. Users can now dock the probe and leave it, freeing the hands. Improved balance for the tools provides a more realistic feel. Smaller tool portals mean the tools won’t physically get in the way of each other when working in a tight space.

“You really can go absolutely everywhere in the knee now,” said ToLTech’s Karl Reinig, PhD, “and you can do the whole diagnostic procedure.”

One important software change is the addition of the mentor, a second program that runs alongside the simulation software and monitors the students’ technique. When students complete a procedure, they receive a percentage grade from the mentor, based on how closely their technique matches a preset level. If a student deviates from the proper technique, the mentor explains what the student needs to do to improve.

Once students are fluent, the mentor compares the time to complete the procedure against a standard time. Students aren’t allowed to progress to the next technique until they can meet that standard.

“By the time students are getting 100 percent scores and matching the community surgeon’s average time, they’re going to be pretty comfortable performing the procedure,” said Dr. Reinig. “I hope that means they can impress the faculty the first time they perform an actual procedure.”

Second nature
Although validation studies were originally scheduled for the end of 2007, the first test (at the University of California San Francisco) is just now getting underway. During 2008, about a half-dozen more medical schools will be testing the simulator.

“Validation may be difficult,” admitted Dr. Reinig. “Residents may have a wide range of capabilities to start with. Will the good ones improve their skills significantly when they use the simulator? How will they do in real surgery? Will we be able to see that the simulator makes a difference?

“I liken it to learning how to play the piano. You can read the music, but playing the song right once doesn’t really mean you’ve really got it down. You need to play that song over and over until it really gets in your head and becomes second nature. That’s what [the simulator] can do if you spend enough time on it.”

ToLTech has a second simulator nearly built. That unit has already been purchased by the Pan Am Clinic in Winnipeg, Manitoba, and should be delivered soon. Residency programs that wish to purchase a simulator outright will spend about $85,000 and will be eligible for regular software upgrades to improve user interface and add enhanced features. Alternatively, residency programs can rent the simulator for a monthly fee of about $15,000.

Peter Pollack is a staff writer for AAOS Now. He can be reached at