What are the reasons for revision surgery?

The decision to perform a revision surgery is based on several factors. After partial knee replacement osteoarthritis may have advanced to other compartments of the knee. After total knee replacement the implant may have become loose, worn or infected. As the implant fails the patient may experience a limp, stiffness, or instability. X-rays or computer imaging may show a change in the position or condition of the implant components. Assessment of these indicators will help determine when knee revision surgery is needed. It’s estimated that over 50% of knee revision procedures will be performed within two years of the initial knee replacement.

• Loosening: Cemented implants can become loose because the cement-bone interface has failed. This is usually due to bone die back, meaning the tiny projections of bone that the cement initially attaches to having either broken off in weight bearing or simply deteriorated due to infection or weak bone (osteoporosis). Non-cemented implants can loosen for much the same reason except it is the implant-bone interface that fails. However, current state-of-the-art materials and techniques have improved the quality of implant fixation to the bone which had historically been a weak link that created a potential site of failure.
• Wear: The plastic parts of knee replacements are softer than the metal and are more prone towards wear during use. Usually this happens after a long period of time as modern plastics (ultra high molecular weight polyethylene or UHMWPE) are very durable and can withstand a considerable amount of wear and impact. Generally speaking, plastic parts are more likely to wear because the accompanying metal parts are not properly aligned, the plastic itself is misaligned, there is a presence of infection, or because they are very old. It is known that wear actually begins from day one after surgery, but the implants can cope with the early stages of wear very well. Implant manufacturers have significantly decreased the amount of wear particles that are created by friction on joint surfaces. However, after several years there may be a build-up of worn off particles which can cause problems in nearby tissues as microscopic fragments get absorbed into the cells and create inflammatory conditions causing pain.
• Infection: With modern surgical techniques the risk of infection from total knee replacement is very low at about 0.5%. If infection does occur, it usually arises due to a substance on the devices called bio-film. This organic material is a microscopic layer of fungal material containing microbes living in a state of hibernation. All implanted devices have this phenomena including items such as stents and pacemakers. Infection arises when the microbes become active and multiply. It is not yet known what provokes this sudden change, but it is known that a series of changes occurs, allowing the microbes reach a state of maturity and become more susceptible to eradication with antibiotic treatment.
• Fractures: Although rare, trauma to the knee may result in a fracture that disrupts the stability of the implant and fixation to the bone which may require surgery to repair.
• Patient-related factors: Rarely do age, activity level, health or being overweight contributes to implant failure. Most knee replacement patients are over 50 years of age and older individuals tend to put lower demands on their implants.