What it is and how common.
Bacteria establishing themselves on or around an implant. It occurs in roughly 1 in 100 primary knee replacements and rather less often after hip replacement, and it is more frequent after revision surgery.
Infection around an implant behaves differently from infection in a normal joint. Bacteria form a biofilm on the metal and plastic surfaces, a layer that antibiotics penetrate poorly and the immune system cannot clear. That is why antibiotics alone rarely cure it, and why treatment usually involves surgery.
Early, delayed and late.
- Early, within about six weeks of surgery. Usually organisms introduced at the time of the operation. Often obvious: a wound that will not settle, discharge, fever.
- Delayed, months to a couple of years. Often low-virulence organisms. Presents as a joint that was never quite right, or persistent pain without an obvious mechanical cause. Easy to miss and frequently mistaken for loosening.
- Late, years afterwards. Usually bacteria arriving through the bloodstream from an infection elsewhere: skin, chest, urinary tract, or dental. Typically a sudden change in a joint that had been fine for years.
When to call the rooms.
Do not wait for the next scheduled review if you have:
- A wound that is discharging, opening or increasingly red.
- Fever, sweats, or feeling generally unwell after joint replacement.
- Pain that is escalating rather than settling.
- New pain in a joint that had been comfortable for months or years, particularly alongside an infection elsewhere in the body.
Early infection treated early has substantially better outcomes than the same infection treated a month later.
How it is diagnosed.
Blood tests for inflammatory markers, radiographs, and above all aspiration of the joint for cell count and culture. Cultures are held longer than usual because some of the organisms involved grow slowly. Where crystals are also present the picture can be confusing, which is why fluid is examined for both.
Antibiotics should not be started before the joint is aspirated unless the patient is systemically unwell, because they can render cultures negative and leave the treatment without a target.
Treatment.
- Debridement with implant retention. For genuinely early infection with well-fixed components: washout, exchange of the plastic bearing, and prolonged antibiotics. Success depends heavily on how quickly it is done.
- Single-stage revision. Everything is removed and new components are implanted in the same operation. Appropriate in selected cases with a known, sensitive organism and good soft tissue.
- Two-stage revision. The standard for established infection. All components and cement are removed, an antibiotic-loaded spacer is placed, targeted antibiotics are given under the guidance of an infectious diseases physician, and a new joint is implanted once the infection is controlled. It takes months.
Treatment is a team undertaking involving the surgeon, an infectious diseases physician and a microbiologist. See revision hip and revision knee replacement.
Reducing your risk.
Before surgery: control blood sugar, stop smoking, reduce weight where possible, treat dental problems, and resolve any skin break, ulcer, tinea or eczema near the joint. Afterwards: treat infections elsewhere in the body promptly rather than waiting them out.
On dental antibiotics, current Australian and international guidance does not recommend routine prophylaxis for most patients with joint replacements. Some patients with specific risk factors are advised otherwise, and that is decided individually.
Common questions.
How common is infection after a joint replacement?
Roughly 1 in 100 primary knee replacements and less often after hip replacement. It is more common after revision surgery and in patients with diabetes, obesity, immunosuppression or a previous joint infection.
Can antibiotics alone cure it?
Rarely. Bacteria form a biofilm on the implant surface that antibiotics penetrate poorly and the immune system cannot clear. Treatment almost always involves surgery as well as antibiotics.
What is a two-stage revision?
All components and cement are removed and an antibiotic-loaded spacer is placed. Targeted antibiotics are given for a period guided by an infectious diseases physician. A new joint is implanted at a second operation once the infection is controlled. It typically takes several months.
What should make me call?
A wound that is discharging or reddening, fever, escalating pain, or new pain in a joint that had been comfortable, especially alongside an infection elsewhere. Call the rooms rather than waiting for your next review.
Do I need antibiotics before the dentist?
Current guidance does not recommend routine antibiotic prophylaxis for most patients with joint replacements. Some patients with specific risk factors are advised otherwise. What matters more is treating dental infection promptly when it occurs.
References.
- Parvizi J, Tan TL, Goswami K, et al. The 2018 definition of periprosthetic hip and knee infection. J Arthroplasty. 2018;33(5):1309-1314.
- Izakovicova P, Borens O, Trampuz A. Periprosthetic joint infection: current concepts and outlook. EFORT Open Rev. 2019;4(7):482-494.
This page provides general information about a medical condition and a surgical procedure. It is not individual medical advice and does not replace consultation with a qualified practitioner. Outcomes vary between individuals and all surgery carries risk. A referral is needed for a consultation with Professor Daevyd Rodda; without one, you can start with the practice nurse practitioner, who can provide it.