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What are the Different Kinds of Prosthetic Joints?

Jeany Miller
Jeany Miller

Joint replacement surgery often relieves pain and improves mobility in patients. Within this field of medicine are othotics and prosthetics, which are respectively used to either support damaged body parts or replace missing limbs and poor joints. Knee, ankle, hip and elbow prosthetic joints are often available for implantation. The life of each of these usually depends upon the patient’s overall health and physical condition. Possible complications with these devices may include implant dislocation, osteolysis and infection.

Orthotics and prosthetics compose a specialized field of replacement medicine. Orthosis often involves a brace that affixes to an existing part of the body. Prosthesis, on the other hand, usually consists of an artificial mechanism used to replace missing limbs or poor joints. Patients who have underdone amputation, suffer from intense arthritis or have congenital birth defects may need one of these reconstructive options.

An X-ray of the pelvic area, showing a metal replacement hip.
An X-ray of the pelvic area, showing a metal replacement hip.

Prosthetic joints are often custom-fabricated to improve a patient's health outcome. In many cases, patients require high-strength and low-weight prosthetic joints for mobility. Materials initially used for aerospace applications often go into the fabrication of these devices. The mechanics of some implants may also reflect the user’s normal activities and personal preferences.

Artificial knees, for example, often have metal, ceramic or plastic components. Electronic knee joints can be programmed in some instances to accommodate individual needs. For example, computer chip located within the joint may sense changes that occur during movement, enabling patients to climb staircases and hills.

During prosthetic knee surgery, the kneecap is often moved so the surgeon can locate the thigh and shin bones. This is the area where the device often fits, and it then attaches to the kneecap. Once the prosthesis is affixed, synthetic bone cement holds it in place. A prosthetic knee joint may last from 10 to 20 years, with routine maintenance in between.

The ankle is another body part that can be replaced with prosthetic joints. These devices are often composed of two parts: the tibial component, which usually replaces the ankle socket, and the talus component, which often replaces the top of the talus bone. A prosthetic ankle is often fashioned from metal and plastic. During the procedure, the surgeon may use epoxy cement to attach the device to the bone. Some surgeons, however, prefer to install the joint with fine holes that allow bone to grow inside and thus attach.

During hip replacement surgery, the damaged joint is often replaced or supplemented with parts that mimic human bone. Components of a prosthetic hip are likely to include a socket, ball and stem. The ball is often metal, and when joined with the metal or plastic socket, movement is likely smooth and effortless.

To install the prosthetic hip, surgeons routinely cut the femur and smooth the damaged bone surface. Once attached, the prosthesis may or may not be cemented for stabilization. In some cases, the surgeon may affix the new hip with a press-fit technique, in which body tissue can grow over it. The life of a prosthetic hip often varies and depends upon such factors as the patient’s body weight, physical condition and activity level.

A prosthetic elbow often consists of two parts connected by a single pin. This forms a hinge, with one section usually fitting into the upper arm and the other fitting into the forearm. The implant often allows the elbow to bend as normal, thereby relieving the pain and stiffness usually associated with arthritis. With a prosthetic elbow, patients are often restricted from some physical activities like contact sports and heavy lifting.

Complications of prosthetic joints may include dislocation of the device or osteolysis, a condition marked by the softening or dissolution of bone. Osteolysis, which often grows worse with time, may predispose a patient to fractures. Surface wear along the bone may occur where prosthetic joints are implanted, and in turn this may cause inflammation, fracture or implant loosening. Infection in prosthetic joints poses grave danger to patients. High mortality rates and costly treatment options are both linked to such infections.

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    • An X-ray of the pelvic area, showing a metal replacement hip.
      An X-ray of the pelvic area, showing a metal replacement hip.