SAN ANTONIO — New prosthetic joint options for rheumatoid arthritis patients are a welcome alternative to conventional silicone implants for relieving pain and restoring function and stability, according to experts at the joint annual meeting of the American Society for Surgery of the Hand and the American Society of Hand Therapists.
New ball-and-joint prostheses relieve arthritic pain and restore articular and bony anatomy, providing more natural hand or forearm-wrist function and appearance and greater stability than provided by silicone implants, which break apart over time and may cause inflammation, said Dr. Richard A. Berger, a professor of orthopedics at the Mayo Clinic College of Medicine, Rochester, Minn., and consultant to Avanta Orthopaedics, San Diego.
Experience with silicone joint implants since their approval in the 1980s have shown that over time the implants tend to break apart, an outcome that can aggravate further inflammatory processes already underway in the joint, said Dr. Berger.
The newer implants promise both to remain structurally intact and to restore articular and bony anatomy, providing a more normal appearance to disfigured hands, said Dr. Robert D. Beckenbaugh, professor of orthopedics at the Mayo Clinic College of Medicine and consultant to Ascension Orthopedics Inc., Austin, Tex.
Dr. Berger noted that the Avanta uHead, replicating the distal ulnar head in the forearm, and the Scheker, a distal radioulnar joint (Aptis Medical, Louisville, Ky.), serve the same purpose but are used in patients with a different degree of problems. The uHead implant is a simple ball on a stem used to replace the end of the ulna when the patient has sufficient bone stock and soft tissue, he said. The Scheker ball-and-socket is used in patients with advanced degenerative rheumatoid disease because it connects directly to the ulnar rather than requiring bone stock or soft tissue to hold it in place.
The Avanta uHead joint is fabricated from a cobalt chrome-molybdenum alloy, and the stem is coated with titanium to promote osseointegration. Provided in right and left configurations and several sizes, the device stem is designed for snap-fit or can be cemented into the socket, which Dr. Berger noted improves the interface in rheumatoid disease patients with soft bone tissue, resulting in a more stable joint than without cement.
The Scheker prosthesis consists of a metal radial plate, socket, and ulna stem as well as an ultra-high-molecular-weight polyethylene ball for complete replacement of the joint, resulting in renewed range of motion that enables patients to use their hands for turning and lifting.
An initial clinical trial by Dr. Berger and Dr. William P. Cooney III, also a professor of orthopedics at Mayo Clinic College of Medicine, followed 26 patients with 28 ulnar head replacement arthroplasties for 30 months. Patients were an average of 51 years old, and all of them presented with pain, instability, or weakness or a combination of symptoms. Eighteen patients got “press-fit” implants, and 10 got cemented implants. At follow-up, 80% of patients were satisfied and reported no pain; 100% experienced improvement in symptoms, but 15% still had mild pain and one patient reported no pain relief. Postoperative pronation and supination of the forearm were 75 degrees and 70 degrees, respectively, and grip strength improved by 10%. There were two acute complications—an ulna shaft nondisplaced split fracture during impaction of the device and an acute dorsal sensory ulnar nerve neuropraxia—and four chronic complications: a neuroma, two cases of residual instability, and one case of implant loosening, all of which required revision surgery. The Mayo Clinic wrist score was used to assess outcomes, which were excellent in 4 patients, good in 18, and poor in 6.
Other options for treatment of hands disabled by arthritis or trauma are pyrocarbon implants for the proximal interphalangeal (PIP), trapeziometacarpal, and metacarpophalangeal (MCP) joints. Both the PIP pyrocarbon total joint and the MCP pyrocarbon total joint prostheses (Ascension Orthopedics) are made from a low-friction pyrolytic carbon-coated graphite substrate compound that has low wear properties and is biologically compatible with bone tissue, said Dr. Beckenbaugh.
The pyrocarbon PIP joint is a bicondylar, semiconstrained prosthesis for total joint replacement with anatomically shaped stems that press-fit into the intramedullary canal to achieve fixation by direct implant-to-bone apposition. The distal component has a bicupped design that allows slight sliding of the proximal condylar component and dorsal extensor to resist subluxation. Distal and proximal components come in four sizes, which can be matched with smaller or larger opposites to best fit the medullary canal of the patient's proximal and middle phalanx.
The pyrocarbon MCP joint replacement builds on pyrolytic carbon arthroplasty technology developed in 1977 but abandoned 10 years later for lack of funding. The new device uses the original MCP implant's simple ball-and-socket design, which had demonstrated very satisfactory results. A few modifications have been made; for example, the stems were enlarged and shaped to be a better physiologic fit with the medullary canal than the original design, the dorsal surface of the joint design was extended 10% to increase stability against volar subluxation, and the pyrolytic carbon material was strengthened through an improved manufacturing process.