Worn Previous Knee Replacement
WHY DOES A TOTAL KNEE REPLACeMENT FAIL?
Total knee replacement is one of the most successful procedures in all of medicine. In the vast majority of cases, total knee replacement enables people to lead more active lives without pain for many years (the rest of their lives for many people). However, over time a knee replacement can fail for a variety of reasons:
Implant loosening - During the original operation the knee replacement implants are either fixed into the surrounding bone with bone cement, or have a coating which allows the body to grow onto the implant (cement-less implants). With time and repetitive stress, the bond between the implant and bone can weaken and cause painful loosening of the implants.
Implant wear - The movement in a knee replacement occurs between the metal femoral component, and the plastic (polyethelene) liner. With time, particularly in older knee replacements, the plastic liner can be worn away which creates tiny fragments of plastic debris within the joint. This debris causes an immune response, which also attacks the healthy bone around the implant and causes it to deteriorate. This leads to loosening of the implants.
Infection - This can be a problem with any surgical procedure, but is particularly problematic when associated with a prosthetic implant. Infections can either get into the knee joint at the time of surgery, or can enter at a later date through the blood stream (from an infection elsewhere in the body). Infection causes painful inflammation of the joint, and can eventually lead to destruction of the bone and loosening of implants. Once stuck to the implants, bacteria cannot be eliminated with antibiotics alone and surgery is required to remove the implants.
Instability - A knee replacement is stabilised by the muscles and ligaments around the joint. As the plastic part of the implant gets worn down with time, the ligaments can become looser, causing the knee to feel unstable. The knee ligaments can also be damaged by an injury or degenerate with age. If this happens, further surgery may be required to put in a more stable (constrained) type of joint.
Fracture - This usually happens as the result of a fall or other significant injury. A fracture in the bone around a knee replacement can cause the implant to loosen.
Patellofemoral (anterior) knee pain - Some people experience pain at the front of their knee when they have had a knee replacement where the kneecap has not been resurfaced. In this situation an operation may be required to place a new lining on the kneecap.
HOW DO I KNOW IF MY KNEE REPLACEMENT IS WORN OUT?
Most of the time a worn-out knee replacement will present as new pain in a previously well-functioning joint. Pain is normally worse with activity, especially the first few steps when getting up from a chair or walking. Your knee may start to make clunking or grinding sounds, get swollen with activity, or buckle and give way when walking. In some cases there can be significant wear in a knee replacement with minimal or no symptoms. If your knee replacement is more than 10 years old it is a good idea to have it checked with x-rays every few years.
HOW IS A WORN-OUT KNEE REPLACeMENT INVESTIGATED?
The best initial investigation of a problematic knee replacement are x-rays of the entire prosthesis. In many cases this is enough to identify the problem. Sometimes further investigations are required to make a diagnosis, or to help plan the revision (redo) surgery. Additional investigations may include:
CT scan
MRI scan
Bone scan or SPECT CT (to show abnormal bone turnover around an implant)
Ultrasound scan
Blood tests
WHAT CAN BE DONE FOR A WORN-OUT KNEE REPLACEMenT?
The decision about the best treatment for a worn-out knee replacement is a complex one. Mr Gormack will need to review your medical records and imaging and make a full assessment of your individual circumstances. In some cases, even if wear and tear is seen on your x-rays, the most appropriate option could be to leave your knee alone. If the worn-out implants are causing a significant problem, or are at imminent risk of failure, further surgery may be required. Any operation to redo a knee replacement is called a revision. This can be anything from a simple change of parts to complete replacement of all implants. Follow this link to learn more about revision knee replacement.