Joint Replacement

        Replacement arthroplasty (from Greek arthron, joint, limb, articulate, + plassein, to form, mould, forge, feign, make an image of), or joint replacement surgery, is a procedure of orthopedic surgery in which an arthritic or dysfunctional joint surface is replaced with an orthopedic prosthesis. Joint replacement is considered as a treatment when severe joint pain or dysfunction is not alleviated by less-invasive therapies. During the latter half of the 20th century, rheumasurgery developed as a subspecialty focused on these and a few other procedures in patients with rheumatic diseases.

        Joint replacement surgery is becoming more common with knees and hips replaced most often. About 773,000 Americans had a hip or knee replaced in 2009.

       Some ceramic materials commonly used in joint replacement are alumina (Al2O3), zirconia (ZrO2), silica (SiO2), hydroxyapatite (Ca10(PO4)6(OH)2), titanium nitride (TiN), silicon nitride (Si3N4). A combination of titanium and titanium carbide is a very hard ceramic material often used in components of arthroplasties due to the impressive degree of strength and toughness it presents, as well as its compatibility with medical imaging.

      Titanium carbide has proved to be possible to use combined with sintered polycrystalline diamond surface (PCD), a superhard ceramic which promises to provide an improved, strong, long-wearing material for artificial joints. PCD is formed from polycrystalline diamond compact (PDC) through a process involving high pressures and temperatures. When compared with other ceramic materials such as cubic boron nitride, silicon nitride, and aluminum oxide, PCD shows many better characteristics, including a high level of hardness and a relatively low coefficient of friction. For the application of artificial joints it will likely be combined with certain metals and metal alloys like cobalt, chrome, titanium, vanadium, stainless steel, aluminum, nickel, hafnium, silicon, cobalt-chrome, tungsten, zirconium, etc. This means that people with nickel allergy or sensitivities to other metals are at risk for complications due to the chemicals in the device.

      In joints such as knee replacements there are two parts that are ceramic and they can be made of either the same ceramic or a different one. If they are made of the same ceramic, however, they have different weight ratios. These ceramic parts are configured so that should shards break off of the implant, the particles are benign and not sharp. They are also made so that if a shard were to break off of one of the two ceramic components, they would be noticeable through x-rays during a check-up or inspection of the implant. With implants such as hip implants, the ball of the implant could be made of ceramic, and between the ceramic layer and where it attaches to the rest of the implant, there is usually a membrane to help hold the ceramic. The membrane can help prevent cracks, but if cracks should occur at two points which create a separate piece, the membrane can hold the shard in place so that it doesn't leave the implant and cause further injury. Because these cracks and separations can occur, the material of the membrane is a bio-compatible polymer that has a high fracture toughness and a high shear toughness.