FDA-approved wrist prosthesis is claimed to
A new total wrist prosthesis, which borrows materials and mechanical concepts from successful hip and knee replacement procedures, was recently approved by the FDA.
Replacing a severely arthritic wrist has always been difficult. Previous implants would sometimes dislocate, despite being cemented in. But now, the Universal 2 Total Replacement System increases both wrist motion and power, while preserving far more bone than was possible with earlier procedures. It has been developed by a team of orthopedic surgeons and engineers at the University of Iowa Orthopedic Biomechanics Laboratory, working with San Diego-based Kinetikos Medical, Inc.
"Our goal was to give the patients as much motion as possible without jeopardizing the stability of the implant" explains codeveloper Nicole Grosland, Ph.D., UI assistant professor of biomedical engineering and orthopedic surgery. "A healthy wrist has two joints. Wrist implants, including the Universal 2, reduce motion to a single joint." By changing the shape of the articulating surfaces and closely mimicking normal wrist anatomy, the designers believe they have managed to increase stability, allow more motion, and even permit implantation without cement through a special coating -- a porous metallic substance designed to allow bone fusion with the prosthesis -- on the implant surface. More than 30 of the prostheses have been implanted to date.
Who's A Candidate?
"The best candidate for a Universal 2 is someone with severe wrist arthritis who is not routinely involved in activities placing high demands on the hand and wrist," says co-developer Dr. Brian D. Adams, professor of orthopedic surgery. Most patients are over 60, but younger individuals are candidates if they have generalized arthritis, such as juvenile rheumatoid arthritis, affecting several joints.
After implant surgery, a patient spends two to three days in the hospital, then two to three months rehabilitating, especially using at home exercises. "A patient achieves approximately one-half of normal motion, which is sufficient for most tasks in the home or office", says Dr. Adams. The Universal 2 recipient, he adds, "should avoid activities that require excessive force or impact, such as carpentry or racquet sports."
Although no negative side effects have yet been reported in a Universal 2 patient, enthusiasm for the new device is not altogether universal. "Trying to recreate a wrist is very difficult--harder than a hip, knee, shoulder or elbow replacement," cautions Dr. Thomas Hunt, section head of Hand Surgery at the Cleveland Clinic. "The problem is that the wrist moves in so many directions and must be able to absorb and transmit a great deal of force in those positions." Dr. Hunt finds that most complications with wrist implants occur over several years, yet new devices can be brought to market without lengthy follow-up studies.
"Fusion has been a very efficient treatment for people with severe pain caused by wrist degeneration. Pain is markedly improved. For patients who have already lost substantial motion, fusion provides a highly functional wrist," says Dr. Hunt. But when both wrists require fusion, he finds the level of function far less acceptable. "If an implant should fail -- as many have-and reconstruction is needed, fusion is much more difficult because bone is sacrificed during the implant procedure and during removal of the prosthesis," he notes. However, Dr. Hunt calls the Universal 2 an improvement over previous wrist prostheses. "We're making progress -- this represents a new, promising implant that may work well in the future." He says. "Time will tell."