The system, called HipNav(TM), or the hip navigation system, was recently used in a limited clinical trial at Shadyside. It will be demonstrated to orthopaedic surgeons at the First American Program on Computer-Assisted Orthopaedic Surgery at Shadyside Hospital, June 12-14.
HipNav employs infrared sensors and a 3-D computerized image system to improve accuracy and reliability when implanting a replacement for the acetabulum, the socket in the pelvis that holds the ball joint of the femur or upper leg bone.
The system is a major research breakthrough at the Center for Medical Robotics and Computer Assisted Surgery (MRCAS), a joint venture of Carnegie Mellon and the Center for Orthopaedic Research (COR) at Shadyside. MRCAS was established in 1993 by Anthony DiGioia, M.D., director of COR, and Takeo Kanade, director of the Robotics Institute at Carnegie Mellon.
The $2.5 million project has been funded primarily by the National Science Foundation. As a result of this work, a clinical trial was initiated recently at Shadyside Hospital after Institutional Review Board approval was obtained.
According to DiGioia, approximately 150,000 total hip replacements are performed each year in the United States alone. One to six percent of them fail because of poor alignment of the components during surgery, which may cause the joint to dislocate or wear abnormally. DiGioia used HipNav for the first time in April to perform a portion of a total hip replacement. Since then, several operations have been performed as part of a clinical trial initiated at Shadyside.
"We are excited because HipNav holds the potential to improve patients' clinical outcomes and also provide for a very precise intraoperative measurement tool," said DiGioia. "Until now, no tools have been available to accurately measure the orientation of the patient's pelvis and the implant. The potential of these new navigational technologies is to reduce complications, make procedures more precise and eventually less invasive. These improvements should result in faster recoveries and less need for repeat surgery."
In total hip replacement surgery, a titanium or cobalt chrome spike topped with a polished ball is inserted into the femur, or upper leg bone, and an orange-sized metal hemisphere lined with smooth plastic is placed in the pelvis. When the ball is placed in the cup, a new hip joint is formed. However, if a surgeon does not align the cup correctly, the patient's hip may dislocate or wear the plastic abnormally.
DiGioia said a key part of the operation's success lies in preoperative planning. The HipNav process involves using 3-D images generated from a preoperative computed tomography (CT) scan to help the surgeon select the optimal implant size and alignment for each patient. A simulator is used to test the motion of the hip joint in advance. Therefore, a surgeon can test and maximize a safe range of motion that will minimize dislocation and wear in the future.
During surgery, HIPNAV provides real-time navigational feedback to the surgeon, based on the location of the patient's pelvis and implant. Once their positions are known, they can be tracked continuously during surgery, eliminating the need for rigid patient positioning on the operating table.
One of the technical challenges is to orient the preoperative plan and CT scan with the position of the patient's pelvis on the operating table--a process called registration. During the operation, HipNav uses the unique surface geometry of the bone to perform this step, which is considered a significant element of the HipNav program. This "surface" registration method--also developed at the MRCAS Center--is used to accurately relate the intraoperative position of the patient to the preoperative plan.
"HipNav combines the strengths of a human surgeon and a robotic system," said Kanade. "A robot or computer measures and computes with great precision and speed. A human is skilled at making overall good judgments and executing a surgical procedure with superb hand-eye coordination.
"HipNav would not have been successful without intense collaboration between technologists and members of the medical profession," Kanade said. "The team was able to overcome the differences in their backgrounds, technical orientation, approach and even culture to ensure the success of this project."
MRCAS at Carnegie Mellon and COR at Shadyside Hospital were formed to foster the application of robotic and computer technologies within medicine. This ongoing work also draws upon additional personnel and resources from other disciplines such as civil and biomedical engineering, robotics and computer science at Carnegie Mellon, and several clinical departments at Shadyside Hospital.
Additional information on HipNav can be accessed on the World Wide Web at http://www.mrcas.ri.cmu.edu, or http://cor.ssh.edu.
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