What Is Joint Replacement Surgery?

Joint replacement surgery is removing a damaged joint and putting in a new one. A joint is where two or more bones come together, like the knee, hip, and shoulder. The surgery is usually done by a doctor called an orthopaedic (or-tho-PEE-dik) surgeon. Sometimes, the surgeon will not remove the whole joint, but will only replace or fix the damaged parts.

The doctor may suggest a joint replacement to improve how you live. Replacing a joint can relieve pain and help you move and feel better. Hips and knees are replaced most often. Other joints that can be replaced include the shoulders, fingers, ankles, and elbows.

Procedural timeline
Before major surgery is performed, a complete pre-anaesthetic work-up is required. In elderly patients this usually would include ECG, urine tests, hematology and blood tests. Cross match of blood is routine also, as a high percentage of patients receive a blood transfusion. Pre-operative planning requires accurate Xrays of the affected joint, implant design selecting and size-matching to the xray images (a process known as templating).

A few days' hospitalization is followed by several weeks of protected function, healing and rehabilitation. This may then be followed by several months of slow improvement in strength and endurance.Early mobilisation of the patient is thought to be the key to reducing the chances of complications such as venous thromboembolism and Pneumonia. Modern practice is to mobilize patients as soon as possible and ambulate with walking aids when tolerated. Depending on the joint involved and the pre-op status of the patient, the time of hospitalization varies from 1 day to 2 weeks, with the average being 4–7 days in most regions.

Physiotherapy is used extensively to help patients recover function after joint replacement surgery. A graded exercise programme is needed initially, as the patients' muscles take time to heal after the surgery; exercises for range of motion of the joints and ambulation should not be strenuous. Later when the muscles have healed, the aim of exercise expands to include strengthening and recovery of function.

Materials
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 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.