Knee Joint Replacement Infections

Knee Joint Replacement Infections

This is called a periprosthetic joint infection and can be a devastating complication of joint replacement surgery.

These joint infections can be associated with significant morbidity, mortality and increased health care costs and a big burden to the patient due to prolonged hospitalisation and multiple surgical procedures over long periods. The periprosthetic joint infection rate for primary joint replacement can be up to 1-2% despite taking every precaution to prevent it.

There are multiple risk factors for periprosthetic joint infections, including:

Patient factors:

A high BMI (body mass index) over 40 increases the risk of joint infections by 3.3 times and if the BMI is over 50, the patient is 21 times more likely to get infected.

Other risk factors for periprosthetic joint infections are malnutrition, diabetes, smoking, ischaemic heart diseases, rheumatoid arthritis with immunosuppressive or steroids, anaemia, alcohol abuse, chronic diseases like kidney failure and socio economic status.

Other surgical factors which can influence infection rates can include the length of the operation, post-operative bleeding or haematoma, the complexity of surgery and tissue handling. However, many months or years after joint replacements, blood-bourne infections from other parts of the body, e.g. a tooth abscess, could also result in joint infection.

How Do Patients Present with Periprosthetic Joint Infections?

There are many ways patients can present when they have a deep-seated joint infection.
Most patients present with warmth and swelling around the joint itself with pain and difficulty mobilising. This can be weeks or months after surgery. Other symptoms include fevers, a wound drainage or wound breakdown and help should be sought straight away.

What Investigations are Done in the Case of Joint Infections?

Once a full history and examination is carried out, blood tests are performed, including blood cultures. Other investigations include x-rays, ultrasound scans where appropriate, or bone or white cell scans, which are performed when relevant.

In some cases the surgeon has to go back into the joint to take samples and send it. This can be done arthroscopically in the case of knee replacements or needle aspirates as well for both knee and hip infections. These samples are sent off for bacterial culture and sensitivity.

What Happens After a Joint Infection is Established?

Treatments can vary depending on the complexity and timing of initial surgery -  whether the infection early after surgery (less than 3 months), 12-24 months or 2 years after.

Most early infections can be addressed with thorough washout with a liner change and multiple debridement and washouts, in addition to 6 weeks to 3 months course of antibiotics. This is called DAIR – debridement, antibiotics and implant retention. Patients who have a long history of symptoms or have sinus tracts are less likely to benefit from this treatment method.

The treatment success of DAIR can range from 31 to 82%. One of the most organisms causing joint infections is Staph Aureus (Methicillin sensitive Staph A – MSSA). There are other organisms causing joint infections, including streptococcus species, coagulase negative staph, anaerobic organisms and MRSA (resistant staph).

What is One-stage Exchange Arthroplasty in Joint Infection?

Some patients can have One-stage Exchange Arthroplasty where the patient can have one operation where the implants are removed and the wound debrided and cleaned before implantation of new prostheses. In this case, the patient has to be healthy, have a known organism grown that is susceptible to antibiotics and have good bone quality and soft tissue envelope.

Patients who have many organisms, poor tissue, immunocompromised or multiple medical comorbidities are not candidates for this procedure, especially if the infection has been long-standing or chronic.

What is 2 Stage Exchange Arthroplasty in Joint Infection?

A two-stage revision or exchange arthroplasty involves removal of the joint replacement prosthesis, temporary cement spacer (antibiotic impregnated) implantation, administration of local and systemic antibiotics for up to 3 months or more, followed by reimplantation of the prostheses after eradicating the joint infection with success rates over 90% in some reported literature.

How Can I Prevent Joint Infections ?

It’s important to reduce the risk factors of joint infections such as obesity, smoking, control diabetes, control heart diseases or chronic health problems and optimise these before surgery with a peri operative-physician.

It is also imperative for patients to ask their surgeon what precautions they should take before, during and after surgery that can reduce the risk of infection.

If the skin over the joint is not prepared well, the surgical approach involves a lot of tissue dissection with bleeding and swelling, in addition to operations that last much longer than the average surgical time, and post-operative bleeding, haematoma or drainage - these factors  increase the risks of joint infections.