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The wrist is different type of joint than the hip or the knee.

• On the hand side of the wrist, there are two rows of bones that connect the end of the forearm to the hand. These bones are called carpal bones, and there are four of them in each row. There is movement between the carpal bones during wrist motion.
• Past the carpal bones are the metacarpals, which sit on the last row of carpal bones, connecting the wrist to the fingers.
• The radius and ulna are the two bones of the forearm that form a joint with the first row of carpal bones; this joint is important in flexing and extending the wrist. The radius, on the thumb side of the wrist, is wider at the wrist than the ulna and makes up the majority of this joint. The ulna, on the little finger (pinky) side of the wrist, is narrower than the radius at the wrist.
• The joint between the radius and ulna, the distal radioulnar joint, is important in the rotation of the forearm.

The ends of the bones at the joints are covered with a smooth, elastic tissue called cartilage. Cartilage creates a slick surface that enables the bones to move smoothly against each other during joint motion. Cartilage can wear out from use over time (like tires on a car) or can be damaged by trauma or disease (e.g., rheumatoid arthritis). Loss of cartilage at a joint is also known as arthritis. In many cases, arthritis is painful and can result in poor joint function. 

(Left) Illustration showing the bones of the wrist and hand. Articular cartilage protects the ends of bones where joints meet. (Right) In this X-ray of a wrist with osteoarthritis, the cartilage is destroyed and the healthy space between bones is narrowed (arrow).

(Left) Reproduced from J Bernstein, ed: Musculoskeletal Medicine. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2003. (Right) Reproduced from JF Sarwark, ed: Essentials of Musculoskeletal Care, ed 4. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2010.

If the cartilage is worn away or damaged by age, injury, infection, or disease, the bones will rub against each other, wearing out the ends of the bones. This causes an often a painful arthritic condition.

• Osteoarthritis, the most common form of arthritis, results from a gradual wearing away of the cartilage covering on bones. Osteoarthritis is typically caused by advanced age and many years of use.

Rheumatoid arthritis of the hand and wrist.

Reproduced with permission from Papp SR, Athwal GS, Pichora DR: The Rheumatoid Wrist: J Am Acad Orthop Surg 2006;14:65-77

• Rheumatoid arthritis is a chronic inflammatory disease of the joints that results in pain, stiffness and swelling. Rheumatoid arthritis usually affects several joints on both sides of the body. it is caused by autoimmune disease that causes the body to attack its own joints.
• Posttraumatic arthritis is caused by trauma or injury to the joints. This form of arthritis is most similar to osteoarthritis. However, the onset of posttraumatic arthritis is less gradual than osteoarthritis and, unlike osteoarthritis, it can be traced back to a traumatic event (e.g., a broken bone during a car accident).

All forms of arthritis may affect the strength and motion of the wrist and result in limited use of the hand.

The typical candidate for wrist replacement surgery has severe arthritis but does not need to use the wrist to meet heavy demands in daily use. The primary reasons for wrist replacement surgery are:

• To relieve pain
• To maintain function in the wrist and hand

Currently available wrist joint replacement implants are much less robust than hip, knee, and shoulder replacement implants. they are not designed for patients with very active lifestyles who lift considerable weight. They work best in patients who do not put a lot of stress on their wrists during daily life.

People who want to remain active and lift considerable weight with their wrist may be better served with a wrist fusion, which removes motion at the wrist but typically results in a strong and painless wrist that can stand up to heavier demands.

Wrist replacement surgery may help retain or recover wrist movements. It may also improve the ability to perform daily living activities, especially if there is arthritis in the elbow and shoulder. During any total joint replacement, the worn-out ends of the bones are removed and replaced by an artificial joint (prosthesis).

Implants

There are several different types of implants. Most have two components, one for each side of the joint. These components are made of metal. A high-quality plastic, called polyethylene, is used as a spacer between the two metal components. Newer implant designs try to replicate the anatomy of the wrist.

• One component is inserted into the radius of the forearm. The portion of this component that faces into the wrist joint has a curve that fits a second component placed on the wrist side.
• The component that inserts into the hand bones (the carpal component) has a flat surface that faces the first component. It inserts into the carpal bones through one long stem and one or two shorter stems or screws.
• The plastic spacer fits between the components in the joint area. Spacers come in different sizes so they can match the patient's wrist size. A spacer is normally flat on one side and rounded on the other. This design enables it to fit into the carpal component while it rocks on the radial component, allowing for wrist motion.

X-ray of a wrist with osteoarthritis before (left) and after (right) wrist replacement surgery using a two-part metal and polyethylene implant.

Reproduced with permission from Carlson JR, Simmons BP: Total Wrist Arthroplasty. J Am Acad Orthop Surg 1998;6:308-315.

X-ray of a wrist with severe rheumatoid arthritis throughout the wrist before (left) and after (right) replacement of the wrist joint with an implant.

Reproduced with permission from Carlson JR, Simmons BP: Total Wrist Arthroplasty. J Am Acad Orthop Surg 1998;6:308-315.

Procedure

Wrist joint replacement can be done as an outpatient procedure, meaning the patient can go home the day of surgery. Wrist replacement surgery can also be combined with other procedures to correct deformities or disorders in the tendons, nerves, and small joints of the fingers, and thumb.

To perform the procedure:

• The surgeon makes an incision is made on the back of the wrist.
• The surgeon removes the arthritic ends of the lower arm bones; they may also remove the first row of carpal bones.
• The surgeon inserts the radial component of the prosthesis into the center of the radius bone on the thumb side of the lower arm. This component is often held in place with bone cement.
• Depending on the component design, the surgeon then inserts the carpal component into the center hand bone (third metacarpal) or screws it into the remaining row of carpal bones. Bone cement may be used to hold the component in place. The carpal bones may be linked or fused together to better secure this component.
• The surgeon inserts an appropriately sized spacer between the metal components.
• At the end of the procedure, the skin is closed. Often, a splint is applied.

Illustration shows the components of a wrist arthroplasty.

You will often need to wear a splint or cast for the first several weeks after surgery. Although pain relief is quick, you will need to do gradual exercises with therapy for several weeks to restore movement and, eventually, to increase power and endurance. 

The physical demands that are placed on the wrist prosthesis will affect the life of the implant. There will be some limitations. For instance:

• You may need to avoid using a hammer or pneumatic tools.
• You will need to limit the amount of weight you lift.
• A fall on the outstretched hand may break the prosthesis, just as it might fracture a normal wrist, so you should avoid activities that could result in a fall.

Although there have been significant advances in wrist prostheses, implants may loosen or fail, due to wear or deformation. In these cases, additional surgery may be necessary.

On average, a wrist replacement can be expected to restore about 50% of normal wrist motion and last 10 to 15 years with careful use. Patients who do not follow restrictions after surgery are more likely to have failures. Thus, patient selection for this procedure is very important to ensure a good outcome.

As with all implants, long-term follow up is advised. Generally, follow up every 1 or 2 years will enable your surgeon to identify any developing conditions or problems.