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.^[1]

Background

Stephen S. Hudack, a surgeon based in New York City, began animal testing with artificial joints in 1939.^[2] By 1948, he was at the New York Orthopedic Hospital (part of the Columbia Presbyterian Medical Center) and with funding from the Office of Naval Research, was replacing hip joints in humans.^[2]

Two previously popular forms of arthroplasty were: (1) interpositional arthroplasty', with interposition of some other tissue like skin, muscle or tendon to keep inflammatory surfaces apart and (2) excisional arthroplasty in which the joint surface and bone were removed leaving scar tissue to fill in the gap. Other forms of arthroplasty include resection(al) arthroplasty, resurfacing arthroplasty, mold arthroplasty, cup arthroplasty, and silicone replacement arthroplasty. Osteotomy to restore or modify joint congruity is also a form of arthroplasty.

In recent decades the most successful and common form of arthroplasty is the surgical replacement of a joint or joint surface with a prosthesis. For example, a hip joint that is affected by osteoarthritis may be replaced entirely (total hip arthroplasty) with a prosthetic hip. This procedure involves replacing both the acetabulum (hip socket) and the head and neck of the femur. The purpose of doing this surgery is to relieve pain, to restore range of motion and to improve walking ability, leading to the improvement of muscle strength.

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^[1] 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.^[3] This means that people with nickel allergy or sensitivities to other metals are at risk for complications due to the chemicals in the device.^[4]

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.^[5]

Risks and complications

Medical risks

The Stress of the operation may result in medical problems of varying incidence and severity.

• Heart Attack
• Stroke
• Venous Thromboembolism
• Pneumonia
• Increased confusion
• Urinary Tract Infection (UTI)

Intra-operative risks

• Mal-positioning of the components
  • Shortening;
  • Instability/dislocation;
  • Loss of range of motion;
• Fracture of the adjacent bone;
• Nerve damage;
• Damage to blood vessels.

Immediate risks

• Infection
  • Superficial
  • Deep
• Dislocation

Medium-term risks

• Dislocation
• Persistent pain;
• Loss of range of motion;
• Weakness;
• Indolent infection.

Long-term risks

• Loosening of the components: the bond between the bone and the components or the cement may break down or fatigue. As a result, the component moves inside the bone, causing pain. Fragments of wear debris may cause an inflammatory reaction with bone absorption which can cause loosening. This phenomenon is known as osteolysis.
• Polyethylene synovitis - Wear of the weight-bearing surfaces: polyethylene is thought to wear in weight-bearing joints such as the hip at a rate of 0.3mm per year. This may be a problem in itself since the bearing surfaces are often less than 10 mm thick and may deform as they get thinner. The wear debris may also cause problems, as inflammation can be caused by increased quantities of polyethylene wear particles in the synovial fluid.

There are many controversies. Much of the research effort of the orthopedic-community is directed to studying and improving joint replacement. The main controversies are

• the best or most appropriate bearing surface - metal/polyethylene, metal-metal, ceramic-ceramic;
• cemented vs uncemented fixation of the components;
• Minimally invasive surgery.

See also

• Rheumasurgery
• Arthroplasty
• Orthopedic surgery
• Joint replacement registry

Specific joint replacements

• Hip replacement
• Knee replacement
• Shoulder replacement
• Ankle replacement

Related treatments

• Autologous chondrocyte implantation
• Microfracture surgery

References

External links

• Patient Information from the American Academy of Orthopedic Surgeons
• Patient Information from the FDA
• P. Benum; A. Aamodt; and K. Haugan Uncementeed Custom Femoral Components In Hip Arthroplasty
• Finkelstein, JA; Anderson, GI; Richards, RR; Waddell, JP (1991). "Polyethylene synovitis following canine total hip arthroplasty. Histomorphometric analysis". The Journal of arthroplasty. 6 Suppl: S91–6. doi:10.1016/s0883-5403(08)80062-9. PMID 1774577.