By: Steve Siwy for Knee1A new computer-assisted navigation system is helping doctors perform knee-replacement surgery with unprecedented accuracy. That’s good news for patients: more accurate positioning of the knee prosthetic means longer-lived knee implants and shorter hospital stays.
Braun's OrthoPilot navigation system, which has been in use for several years in Europe, is now gaining ground in the U.S. It takes measurements and displays patient-specific information and graphics during surgery, guiding her hand with computer precision. As a result, doctors are now able to achieve nearly 100-percent accuracy when positioning and aligning knee-replacement implants.
Knee-replacement surgery may be recommended by doctors if knee pain or loss of function (for instance, due to osteoarthritis) cannot be alleviated by more moderate treatments, such as medication, exercise, or heating pads and ointments. According to the American Academy of Orthopaedic Surgeons (AAOS), 299,000 total knee replacements were performed in the year 2000, and the number grows every year.
Doctors have traditionally used manual measurements and visual cues to line up the prosthesis during surgery, which are sometimes supplemented by images from previous CT scans or X-rays. Even though care is taken, about ten percent of knee replacements are misaligned (out of alignment by more than three degrees). Misalignment can lead to longer recovery and rehabilitation times after surgery, greater patient discomfort, and increased wear on the knee implant.
The OrthoPilot allows the surgeon to dispense with estimation and visual measurements, supplying him with a much more precise stream of computer-generated data. Says Dr. David Stulberg, of Northwestern Memorial Hospital, “The computer knows the length of the bone, it knows the shape of the bone. It can tell you how much you need to cut and what direction you need to cut.”
To use the OrthoPilot, the surgeon first places the patient’s leg in a holding sleeve, which is screwed into place on either side of the knee. Transmitters are placed along the leg, and their locations are tracked by an infrared camera. A screen displays a computer model of the leg, and the navigation system guides the surgeon throughout the procedure: cutting bone, placing the implants, and aligning the leg. Any misalignments are displayed, and corrections suggested, in real time. It is thus possible for the surgeon to make much finer adjustments when implanting and aligning the knee prosthesis than with the traditional method. As a result, patients whose doctors use the system experience less pain, shorter rehabilitation time, and less likelihood of needing another, “revision,” knee replacement later in life.
Along with better-aligned joints, use of the OrthoPilot provides other benefits to patient and surgeon, as well. Because it takes all its measurements during the surgery, the OrthoPilot system removes the need for pre-operation examinations or imaging, such as CT scans or X-rays, which can be expensive, as well as time-consuming. The computer-generated measurements also have the advantage of being interactive, unlike previous static-imaging methods, and far more precise than, for instance, an X-ray.
Additionally, the rising prevalence of minimally invasive procedures has meant smaller incisions, which reveal less of the surgical site to the operating surgeon. The OrthoPilot system helps the doctor regain, and indeed improve upon previous visibility, without having to increase the size of the incision. These advantages come at the price, on average, of only about 10 total minutes added to the length of the knee-replacement procedure.
