Knee joint replacement is one of the most well-established and successful surgeries in the world. But like any medical procedure, it comes with a small amount of risk.
One of these is infection: when bacteria get into the wound, or even into the implant itself. Fortunately, the chances of this happening are low. The National Joint Registry puts the risk of infection after a knee replacement at less than one percent. All the same, since infections can be potentially serious, it’s helpful to know how we might deal with them if they happen. Here’s an overview.
What are the symptoms of an infection?
It depends on the type. An important question to ask at the outset is: is this a superficial or a deep infection? A superficial infection might simply involve some localised inflammation around the wound. This can be treated with oral antibiotics if we feel it’s a concern. A deep infection is more serious and may involve a wider range of symptoms. This can include things like swelling, reddening around the knee, pain, feeling unwell or feverish, and difficulty in moving the joint.
How do you diagnose knee infections?
There are a few different options. We can do some blood checks, including one called a C-Reactive Protein test (CRP), to see if your “inflammatory markers” are raised. Inflammatory markers are substances that the body produces in response to infection-related inflammation. We can also take some fluid from the knee and send it to a laboratory for analysis. The lab can test for the presence of bacteria, and whether your level of white blood cells is raised (another potential sign of infection). We may also order an x-ray to determine if there’s an infection in the implant.
What happens if the infection gets into the implant?
The issue with this type of infection is that it can be difficult for the body to fight off the bacteria naturally. Because the new joint is made of artificial elements like plastic and metal, there’s limited blood flow to the area. This means there’s less opportunity for the immune system to get to work on the bacteria and stop it from establishing itself in the new joint.
So how does the treatment work?
The most common treatment approach is a procedure called debridement. This is essentially a sterilised surgical washout of the infected joint. Here’s how it works:
- Remove infected tissue – first, the surgeon opens the knee and carefully removes the lining of the knee joint. This will help to get rid of any infected tissue around the implant
- Analyse samples – next, they take some samples for the laboratory. The microbiology team will use these to identify the bacteria and determine the best course of antibiotics after surgery
- Clean implant – finally, they use a “pulsed lavage” system to pass several litres of saline solution over the implant. This sterilised salt-water solution helps to kill off bacteria in the implant
What happens after the debridement?
It varies from patient to patient. But a typical programme would be at least two weeks of intravenous (IV) antibiotics, either at home or in hospital so the doctors can monitor progress. That might be followed by a further month of oral antibiotics. The team will also be carrying out more tests to check that inflammatory makers are falling as you’d expect after the infection has been eliminated.
Are there alternatives to debridement?
Debridement is most effective if the infection is caught early – ideally within the first few days. Longer-lived infections can be more difficult to eliminate. In the most serious cases, they can sometimes lead to revision surgery. This is where the implant is taken out and replaced with a new one. There may be a period of IV antibiotic treatment in the lead-up to the revision too. Though infection-related knee revisions do happen – we see them here at the clinic on occasion – it’s worth reiterating that they are really quite rare. Most infections are straightforward to tackle and respond well to treatment. And, these days, there’s a wide range of options available to deal with them swiftly and effectively.
