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Revisions: what makes them necessary?


Nurse Director
Jun 8, 2007
The North
United Kingdom United Kingdom
Why do implants fail?

There are several reasons for the failure of joint replacements. Some of these reasons include wear, loosening, infection, fracture, instability, and patient related factors:

Wear and Loosening: Properly functioning implants depend on their appropriate fixation to the bone; fixation is usually achieved by cementing the implant onto the bone. Some surgeons prefer to use uncemented devices.

Although implants are firmly fixed at the initial surgery, they may become loose over time. Friction caused by the joint surfaces rubbing against each other wears away the surfaces of the implant, creating tiny particles that accumulate around the joint. In a process called aseptic (non-infected) loosening, the bond of the implant to the bone is destroyed by the body's attempt to digest the wear particles. During this process, normal bone is also digested (a condition called osteolysis), which can weaken or even fracture the bone.

When the prosthesis becomes loose, the patient may experience pain, change in alignment, or instability. Aseptic loosening is the most common mode of failure of joint replacements.

Infection: Infection is a devastating complication of any surgical procedure. In joint replacement, the large foreign metal and plastic implants can serve as a surface for the bacteria to latch onto, inaccessible to antibiotics (Infection: peri-prosthetic infection - also known as late onset infection). Even if the implants remain well fixed, the pain, swelling, and drainage from the infection make the revision surgery necessary. With current surgical techniques and antibiotic regimens, the risk of infection from total knee replacement is less than 1%.

Revision surgery of the infected knee takes several forms. Depending on the degree of infection and damage, the decision is made to either perform a simple washout of the knee with component retention or complete exchange of the implants.

In most cases, two separate operations are required: first to remove the old prosthesis and insert a block of cement with antibiotics (known as an antibiotic-impregnated cement spacer) and a second surgery to remove the spacer and insert a new prosthesis. Intravenous antibiotics are given during this period to eradicate the infection.

Fractures: The type and extent of the fracture will determine if revision surgery is needed. Peri-prosthetic fractures are fractures around the implants that disrupt the fixation or the stability of the implant. They may require revision surgery or they might be able to be treated with just rest and a period of non-weightbearing.
Prosthetic fractures: (More common in hips) mostly occur in the stems and though they can be due to wear, are more likely due to an imbalance of the entire replacement. Falls and road accidents also figure in the causes.

Instability: Instability occurs when the soft-tissue structures around the joint are unable to provide the stability necessary for adequate function during standing or walking. Instability may be the result of increased soft-tissue laxity (looseness), inadequate flexion of the implants, or improper positioning or alignment of the prosthesis. Pain and/or a sense of “giving away” of the knee may alter function and require revision surgery.

Patient-Related Factors: Age, activity level, surgical history, and weight can contribute to implant failure. Younger, more active patients have a higher rate of revision than older, less active patients. Obese patients have a higher incidence of wear and loosening. Patients with previous knee surgeries are at higher risk for infection and implant failure.

What are the signs?

A failed implant is usually indicated by an increase in pain or a decrease in function. Persistent pain and swelling can indicate loosening, wear, or infection, and the location of the pain can be all over the knee (generalized) or in one particular area (localized). The decline in function may result in a limp, stiffness, or instability. Patients who demonstrate these symptoms and signs may require revision joint surgery.


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