What to do when your hip or knee replacement wears out

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Hip or knee replacement surgery has the potential to renew a patient’s quality of life by alleviating pain and allowing increased function of the joint. It is a common procedure performed by orthopedic surgeons. While hip and knee replacement surgeries offer excellent results, the replacements can wear out over time, just like natural joints.

Implant systems today are built to last and function under higher activity levels than previous technology. However, as with any man-made mechanical part, they do wear out. Like brakes on a car, the plastic liners at the bearing surface of the joint replacement wear with time and use. Typically, they last 20 years or more, but not always.

A hip replacement is designed to replicate the ball and socket of the normal hip anatomy. The hip implant consists of a component that fits into the pelvic socket, commonly a metal cup with a plastic polyethylene lining, and a metal or ceramic ball secured on a stem that fits within the thighbone (femur). Knee implants are designed to replicate the anatomy of the knee. The ends of the knee joint bones (femur and tibia) are resurfaced with metal, and a plastic polyethylene liner is then fixed between them.

As normal wear and use occur, the metal rubbing against the polyethylene plastic lining can result in the degradation of the plastic and cause small plastic particles to flake off. The body’s immune system can react to the particles as foreign matter by attacking them. Since the particles typically settle near the implant, the immune system also attacks the surrounding bone, a process known as osteolysis. As bone loss occurs, the hip or knee implants can loosen and begin to function improperly. Typically, this phenomenon is associated with pain.

Polyethylene wear and osteolysis is a significant cause of hip or knee implant failure. However, there are other causes of implant failure including infection, malalignment, trauma, and instability. The most prominent symptom of a problematic joint replacement is pain. For those that have had a knee or hip replacement, it is important to note that continuous or sudden onset of pain after a joint replacement may be caused by many factors. Patients who experience recurrent or sustained pain should visit an orthopedic surgeon. Delaying a visit might make fixing the problem more difficult.

When implant failure occurs, another surgery is typically required to replace the failed implant. Since valuable bone can be lost or degraded when an implant fails, revision surgery is generally more complicated than the primary or original replacement.

Though the procedure for revision surgery is similar to primary joint replacement, there are key differences:

• Revision surgery takes longer than the primary surgery as it is often more complicated.
• Joint aspiration (removing fluid from the joint) may be necessary to test for infection.
• Revision surgery carries a higher risk of potentially needing a blood transfusion.
• Since revision surgeries are typically extensive and significantly invasive, an extensive pre-op examination is often necessary.
• The risk of complications is greater and the recovery period longer.
• A revision often necessitates the replacement of lost bone either through bone grafting or the use of special implants.
• Implants may be cemented or uncemented but the design of the implant may differ from the original implant.

Since revision joint replacement surgery is typically more difficult, it is imperative to have an experienced surgeon and seasoned surgical team on your side before, during and after surgery. To consult with an orthopedic surgeon with expertise in revision joint replacement, call Portneuf Orthopedics at (208) 239-2620 or visit Portneuf.org/ortho to schedule an appointment.

— Cody Martin, MD