By its nature, arthroscopic surgery is a procedure that allows surgeons to repair or remove tissue from a joint with minimal disruption to other critical parts.
The surgeon inserts instruments and a small camera through tiny portals or incisions, monitoring the instruments’ movements on a television screen. The procedure generally presents a lower risk of infection and blood loss, reducing the recovery time for patients.
Performing arthroscopic surgery on the hip joint, however, presents more challenges for surgeons than minimally invasive surgery on other joints, noted Emily Geist, Class of ’03, and an assistant professor of mechanical engineering at Bucknell University.
“The hip is a lot deeper in the body than the knee or shoulder, and it’s a lot tighter,” Geist said. “The hip has a ball and socket. It’s a little more difficult to get an instrument in there. There is a navigation challenge often times when you are that deep in the body.”
Geist, who has master’s and doctoral degrees in mechanical engineering from Carnegie Mellon University in Pittsburgh, is working on a computer-aided arthroscopy system to perfect arthroscopic surgery. She is collaborating with her graduate adviser from Carnegie Mellon, Kenji Shimada, who hatched the idea with a surgeon at the University of Pittsburgh Medical Center. The team is pursuing a patent.
Geist and Shimada have published their findings in articles, including “A study of user performance employing a computer-aided navigation system for arthroscopic hip surgery,” which appeared in the International Journal of Computer Assisted Radiology in December 2007 and “Computer-aided navigation for arthroscopic hip surgery using encoder linkages for position tracking,” in a September 2006 edition of the International Journal of Medical Robotics and Computer Aided Surgery.
Assistant Professor of Mechanical Engineering Emily Geist ’03 demonstrates how a computer-aided system assists in arthroscopic hip surgery
In traditional arthroscopic surgery, the surgeon sees only what the small camera inserted through the portal sees, Geist said. That makes it more difficult for a surgeon to navigate within the joint, avoiding the delicate sciatic nerve and femoral vein and artery in that region.
The system, which has been tested only on a model so far, includes a computer simulation that provides views of a hip joint from several angles and sets off alarms – in the form of a red screen – when an instrument gets too close to nerves, arteries and veins. The images in later iterations of the system will be based on information from the CAT scans, MRIs or X-rays of individual patients.
“Instead of looking at one tiny image, you can see all different images,” Geist said. “It shows where the tool is relative to the hip bone and the vein and artery. As you’re moving the tools around, the encoder linkage captures the motion of the tool. The system restores some of the vision that’s been lost in arthroscopy versus open surgery.”
Inspired by a toy
Shaped like a metal chain with S-shaped links, the device was inspired by the children’s “tangle toy” (tanglecreations.com), which Shimada thought would make a good model for a small, flexible surgical tracking instrument, Geist said. After talking with the surgeon, Shimada and Geist focused on developing a mechanical tracking linkage using rotational encoders. The encoders record subtle movements of instruments as they move inside the body. The simulation interprets the movements as they correspond to the patient’s anatomy.
Geist and Shimada conducted tests of the system with subjects who are not surgeons. They assigned the test groups tasks such as navigating the instruments from one part of the hip bone on a model to another part, using the computer-aided arthroscopy system as a guide. The time needed to complete the procedure was cut by 38 percent when using the system, Geist said. Additional testing would have to be conducted before the system could be marketed.
In addition to the possibility of perfecting arthroscopic surgery, Geist and Shimada believe the system could be used as a training tool.
The team continues to work on improving the design of the medical device. One idea is to add additional guidance for the surgeon such as suggesting an optimal path to the hip joint. “The goal is not to replace the surgeon but to optimize the procedure,” Geist said.