Each year more than 700,000 joint replacements are performed in the United States. About 10% of joint replacement physicians are using the computer-assisted method for total and partial joint replacements, primarily in the knee. The percentage of computer-assisted joint replacements is rising.

“It gives you the ability to get things straight,” said William G. Ward, one of the physicians who use computer-assisted surgery. “There are very few ‘redos’ if the bones and joints are lined up within 3° or less.” Dr. Ward recently served as the narrator for a computer-assisted total knee replacement done by orthopaedic surgeon Jason E. Lang, M.D., during a webcast. The webcast is available online at wfubmc.edu/webcasts.

About 97% of knee replacements are performed because of osteoarthritis that has badly damaged the joint, often leaving patients without cartilage, just bone on bone. The remaining 3% are performed for other reasons, including rheumatoid arthritis, injuries and congenital conditions.

In some cases, only a partial joint replacement is done if one side of the knee is worn out or damaged. That is referred to as a uni- or single-compartmental or uni-knee. It is most often the medial or inner side that wears out first.

The advantage of working with the computer is that it tells the physician where to cut and how deep. It also shows the alignment of all of the leg joints, which should have a straight line from the center of the hip joint, through the center of the knee joint to the center of the ankle joint.

During computer-assisted surgery, the physician is guided by spheres near or on the joint that give readings on a nearby computer screen. For a total knee replacement, the computer guides the physician on how much of the femur and tibia to trim away and exactly where to place the metal plates. These metal pieces are glued onto the top of the tibia and the bottom of the femur, and a ceramic or plastic piece is placed in between.

The metal pieces are typically titanium- or cobalt chromium-based alloys. These replacement joints have a 95% chance of lasting 10 to 20 years or more. “Using the computer allows me to know that I have aligned the person’s knee properly, which will allow the prosthesis to last a long time,” said Dr. Jason E. Lang, one of the orthopaedic surgeons who does computer-assisted joint replacement. “It gives me confidence that I have done the best job I possibly can.”

Riyaz Jinnah, M.D., the orthopaedic surgeon who directs the Joint Replacement Program at Wake Forest University Baptist Medical Center, said that computer-assisted joint surgery has a great future. “It tells you where to cut and gives you real-time feedback,” Dr. Jinnah said. “One of the reasons we are getting ready to concentrate on the computer-assisted surgery for the uni-compartmental knees is that that particular surgery is one of the most technique dependant. You have to get it right.”

The next step will be to develop a robot for resurfacing, Dr. Jinnah said. Robots are already being used at Wake Forest Baptist for a variety of urological surgeries, such as prostatectomies, and for mitral valve surgery. “We are very keen on developing other applications for robots,” Dr. Jinnah said.