ARTHROPLASTY
Prosthesis
With joint replacements, there is a wide range of options available for prostheses. The many materials that may be used include:
- Polyethylene. This has been the most common material used in prostheses. However, it has been heavily scrutinized because of its high production of wear debris, which leads to osteolysis (enzymes break down and reabsorb the bone tissue in an attempt to get rid or foreign particles).
In the past, this wear rate has been very high, but because of improvements in sterilization and development, new polyethylene designs have become much more resistant to wear. Still newer developmental designs demonstrate even less wear but require further long–term study. Polyethylene is the least expensive material for prostheses.
- Metal alloys. Chromium cobalt is often used, but stainless steel or titanium may also be employed. These metals produce very small amounts of wear debris and the wear rate actually improves once the prosthesis has been broken in. Metal alloys may still cause osteolysis, but to a smaller degree than polyethylene. Any metal surface, including the metal alloys used in prostheses, may generate corrosion, but this is typically reduced, especially in newer designs.
There is some concern over the absorption of metal ions in the body. These ions may be deposited throughout the body and metallic levels in the blood and urine may be many times higher than normal. No adverse effects have been reported over 20 years of use in any individual, but this issue requires further study.
- Ceramics. Alumina is typically used. Ceramics are more brittle than other materials used for prostheses but have lower wear rates than metal. However, though they do generate less debris, they may still cause osteolysis. Little is known about the response of the body to ceramic wear particles.
- Carbon. Pyrolytic carbon and graphite have been used successfully in small joint implants and can be incorporated into composites of larger implants.
A prosthesis may incorporate any of a number of designs, including:
- Metal-on-polyethylene. This is the most commonly used prosthesic design. It has a low coefficient of friction close to that of normal joints and typically lasts for about 20 years.
- Metal-on-metal. The earliest prosthesis designs were metal-on-metal. These early designs showed many failures, generally due to design flaws and the misunderstanding of how specific joints work. The designs were nearly replaced by metal-on-polyethylene designs as a result. However, metal-on-metal regained popularity when polyethylene particles were linked to osteolysis. These designs typically last for about 20 years.
- Ceramic-on-ceramic. These designs were initially investigated for high scratch resistance and wearability. Early designs had many problems with cracking, but this fracture problem has been nearly eliminated in current designs. Ceramic-on-ceramic prostheses typically last for about 15 years but have not yet been approved for widespread use in the United States.
- Silicone spacers. These are typically reserved for very small joints, such as the knuckles. This is a one-piece design rather than a hinge. Small silicone discs are placed between the bones of the joint to cushion them and keep them from rubbing together. Over time, the soft tissues and ligaments around the joint heal and strengthen and joint movement and function is partially regained. Silicone spacers typically last about 10 years.
A final option in the choice of prosthesis lies in the method used to adhere the prosthesis to the bone. These options include:
- Bone cement. Polymethylmethacrylate (PMMA) is used to secure the prostheses to the bone. It may wear and cause osteolysis and has higher rates of loosening than with press fit. The decision on whether to use bone cement is often dependent on the clinical situation and the surgeon’s preference. Though cemented components are currently the most popular method of fixation, cementless components are becoming increasingly popular.
- Press fit. This cementless approach encourages bone to grow directly into the prosthesis. The prosthetic surface is rough, to increase surface area, and coated in an osteoconductive substance, such as hydroxyapatite, that encourages the bone to grow and adhere to the surface.
- Hybrid approach. Bone cement is used on part of the joint and press fit on the other.
Arthroplasty, hip arthroplasty, total hip arthroplasty, knee arthroplasty, total knee arthroplasty, Fahri Erdoğan, Fahri Erdogan, Fahri Erdogan MD, Ortopaedic Surgeon, Ortopaedic Surgeon Professor, Arthroplasty , Artroplasti.net, Orthopaedics and Travmatology, The Best orthopaedic surgeon professor, nişantaşı ortopedi merkezi, nomerk, istanbul üniversity, memorial hospital, cerrahpaşa medical faculty, osteotomy, trademark, arthroscopic surgery, osteoarthritic pain, prosthesis, joint replacement, quality of life, hip fractures, acute trauma, rheumatoid arthritis, cartilage, bone, Osteoarthritis, Fractures, osteoporosis, osteonecrosis, Hip dysplasia, Joint deformity, TMJ disorder, Psoriatic arthritis, Sports injuries, Total joint arthroplasty, x-ray, conservative therapies, Single-stage bilateral total joint arthroplasty, Unilateral total joint arthroplasty, Hemiarthroplasty, Unicompartmental joint arthroplasty, Minimally invasive surgery, Replacement arthroplasty, Polyethylene, Metal alloys, Chromium cobalt, stainless steel, titanium, metal ion levels, Ceramics, Alumina, Carbon, Pyrolytic carbon, graphite, small joints, Metal-on-polyethylene, Metal-on-metal, 20 years, Ceramic-on-ceramic, Silicone spacers, Bone cement, Polymethylmethacrylate, PMMA, Press fit, autologous blood donation, Arthrography, Magnetic resonance imaging, Bone scan, osteophytes, inflamed synovium, recovery room, limit weight bearing, immobilization devices, NSAIDs, Analgesics, Physical therapy, circulation and nerve function, occupational therapy, Antibiotics, restore function, Thromboembolism, deep vein thrombosis, Infection, Osteolysis, Ossification, Periprosthetic fracture, Prosthetic break, Aseptic loosening, Dislocation, Nerve damage, Vascular injury, Leg-length discrepancy, joint braces, Arthroscopy, osteotomy