Joint replacement

For shoulder replacement, there are a few major approaches to access the shoulder joint. The first is the deltopectoral approach, which saves the deltoid, but requires the supraspinatus to be cut.[2] The second is the transdeltoid approach, which provides a straight on approach at the glenoid. However, during this approach the deltoid is put at risk for potential damage.[2] Both techniques are used, depending on the surgeon's preferences.

The number of shoulder replacements carried out each year is increasing, but research looking into global records suggests that nine out of ten shoulder replacements last for at least a decade.[3][4]

Hip replacement can be performed as a total replacement or a hemi (half) replacement. A total hip replacement consists of replacing both the acetabulum and the femoral head while hemiarthroplasty generally only replaces the femoral head. Hip replacement is currently the most common orthopaedic operation, though patient satisfaction short- and long-term varies widely.

It is unclear whether the use of assistive equipment would help in post-operative care.[5]

Knee replacement.

Knee replacement involves exposure of the front of the knee, with detachment of part of the quadriceps muscle (vastus medialis) from the patella. The patella is displaced to one side of the joint, allowing exposure of the distal end of the femur and the proximal end of the tibia. The ends of these bones are then accurately cut to shape using cutting guides oriented to the long axis of the bones. The cartilages and the anterior cruciate ligament are removed; the posterior cruciate ligament may also be removed but the tibial and fibular collateral ligaments are preserved.[6] Metal components are then impacted onto the bone or fixed using polymethylmethacrylate (PMMA) cement. Alternative techniques exist that affix the implant without cement. These cement-less techniques may involve osseointegration, including porous metal prostheses.

The operation typically involves substantial postoperative pain, and includes vigorous physical rehabilitation. The recovery period may be 6 weeks or longer and may involve the use of mobility aids (e.g. walking frames, canes, crutches) to enable the person's return to preoperative mobility.[7]

Ankle replacement has become a treatment of choice for people requiring arthroplasty, replacing the conventional use of arthrodesis, i.e. fusion of the bones. The restoration of range of motion is the key feature in favor of ankle replacement with respect to arthrodesis. However, clinical evidence of the superiority of the former has only been demonstrated for particular isolated implant designs.[8]

Finger joint replacement.

Finger joint replacement is a relatively quick procedure of about 30 minutes, but requires several months of subsequent therapy.[9] Post-operative therapy may consist of wearing a hand splint or performing exercises to improve function and pain.[10]

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)

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

• Infection, either Superficial or Deep
• Dislocation

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

• 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 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.

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.[11] This means that people with nickel allergy or sensitivities to other metals are at risk for complications due to the chemicals in the device.[12]

In knee replacements there are two parts that are ceramic and they can be made of either the same ceramic or different ones. 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.[13]

The prosthesis may need to be replaced due to complications such as infection or prosthetic fracture. Replacement may be done in one single surgical session. Alternatively, an initial surgery may be performed to remove previous prosthetic material, and the new prosthesis is then inserted in a separate surgery at a later time. In such cases, especially when complicated by infection, a spacer may be used, which is a sturdy mass to provide some basic joint stability and mobility until a more permanent prosthesis is inserted. It can contain antibiotics to help treating any infection.[14]