Joint Prosthesis Infection
What Is a Joint Prosthesis Infection?
A joint prosthesis infection (periprosthetic joint infection) is an infection of the implant and the surrounding tissues in an artificial joint such as a knee or hip replacement. Knee and hip replacements are among the most common planned operations and relieve pain and restore movement for most patients, but no surgery is completely without risk.
A prosthesis infection occurs in only a small proportion of patients, but it is a complication that must be taken seriously. It can develop in the superficial wound or in the deep tissues around the implant, and it may appear during the hospital stay, after returning home, or even years after surgery. For general information about hip and knee replacements you can review the hip and knee condition pages.
How Does the Infection Develop? Biofilm
Infections are caused by bacteria. Bacteria normally live on our skin and in our digestive system and are kept under control by the immune system. The metal and plastic surface of an implant, however, is hard for immune cells and antibiotics to reach.
Bacteria can attach to the implant surface and form a protective layer called biofilm. Bacteria inside the biofilm become resistant to antibiotics and to the immune system, which is why deep infections that settle on an implant usually cannot be cleared by antibiotics alone and require surgery. Bacteria can reach the joint through the bloodstream from cracks and cuts in the skin, major dental work, urinary tract infections or other surgical procedures.
Risk Factors
Infection can develop in anyone, but certain conditions raise the risk. Some of these factors can be improved before surgery to reduce that risk.
- Diabetes and poorly controlled blood sugar.
- Obesity and poor nutrition.
- Conditions and treatments that suppress the immune system (HIV, lymphoma, chemotherapy, long-term corticosteroids).
- Smoking and peripheral vascular disease and other conditions that impair wound healing.
- Inflammatory joint disease, previous surgery on the same joint and prolonged operating time.
Symptoms
Symptoms depend on whether the infection appears early or late. In early infections wound problems and general signs of infection are prominent, whereas in late infections the only symptom may be steadily increasing pain in the joint.
- Increasing pain or stiffness in a joint that previously worked without problems.
- Swelling, warmth and redness around the wound.
- Drainage from the wound (blood, pus or clear fluid) or a wound that does not close.
- Fever, chills and night sweats.
- Fatigue and a general feeling of being unwell.
New or steadily increasing pain in a replaced joint should always be assessed; the source of the pain may be loosening, a mechanical problem or infection, and telling them apart determines the treatment.
Early, Delayed and Late Infections
Infections are grouped by when they appear after surgery, and this classification directly affects the treatment decision. Early (acute) infections usually appear in the first weeks, and if the implant is well fixed they can sometimes be treated while keeping the implant.
In delayed and late (chronic) infections the biofilm is firmly established, so keeping the implant is usually not possible and removing it comes onto the agenda. Sudden (haematogenous) infections that arrive through the bloodstream from a distant source present with pain that starts abruptly and signs of infection in a previously well-functioning prosthesis.
Infection or Loosening? Making the Distinction
The two most common causes of pain in a replaced joint are infection and mechanical loosening; they can look similar but their treatments are completely different, so the distinction is critical. In aseptic (non-infected) loosening the pain usually increases with weight-bearing and movement and eases with rest, and there are no signs of infection such as fever, redness or drainage.
In infection the pain may continue at rest and at night, is often accompanied by inflammatory signs, and blood tests and joint-fluid analysis help point the way. A revision is not planned until the source of the pain is clarified, because if an infection is missed the newly placed prosthesis will meet the same problem.
Diagnosis: Examination and Tests
Early and accurate diagnosis improves the chance of saving the implant. Assessment begins with the history and physical examination; then several tests are interpreted together, because no single test gives a definite answer on its own.
- Blood tests: C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) support a suspicion of infection but do not diagnose it on their own.
- Imaging: X-rays can show implant loosening and bone changes; bone scans are used in selected cases.
- Joint-fluid analysis: fluid taken from the hip or knee is examined for cell count, culture and special markers, and this is one of the most valuable steps in diagnosis.
- Tissue cultures: samples taken during surgery are cultured to identify the responsible organism and the appropriate antibiotic.
Non-Surgical Treatment
In early superficial infections that involve only the skin and superficial tissues and do not reach the implant, appropriate antibiotic treatment may be enough. When caught early, this approach is often successful.
Deep infections around the implant, however, cannot be cleared by antibiotics alone because of the biofilm. In these cases antibiotics are a part of treatment that complements surgery; the type and duration of antibiotic are decided by the culture results. Antibiotics are always chosen under medical supervision based on cultures, and the course is completed as advised by the doctor.
Surgical Treatment
Deep infection requires surgery. The method is chosen according to how early the infection is, whether the implant is well fixed, the responsible organism and the patient's general condition.
- Debridement and implant-retaining surgery (DAIR): in early infections with a well-fixed implant, the infected tissue is cleaned, mobile parts may be exchanged and the implant is kept, followed by a prolonged course of antibiotics.
- Two-stage revision: the most common approach in chronic infection. The implant is first removed, the joint is cleaned and an antibiotic spacer is placed; once the infection is under control a new prosthesis is fitted at a second operation.
- One-stage revision: in selected cases the old implant is removed, the joint is cleaned and a new implant is placed during the same operation.
In advanced cases where the infection cannot be controlled or where there have been several failed attempts, larger operations may be considered. These decisions are made on an individual basis. For other surgical situations related to prostheses, the pages on fracture after hip replacement and revision arthroplasty give more detail.
Recovery Process
Recovery depends on the surgery performed and the severity of the infection. It is shorter when the implant is kept in a debridement, whereas a two-stage revision requires a period of antibiotics and healing lasting weeks between the two operations.
Throughout the process, adherence to antibiotic treatment and follow-up with regular checks and blood tests are important. Protection against clots after surgery is also part of the plan; the deep vein thrombosis page gives general information on this. The goal of recovery is a pain-free, infection-free and functional joint.
Preventing Infection
The surgical team takes many measures to reduce the risk of infection during surgery: appropriate antibiotics before and after the operation, careful sterilisation, keeping operating time short and, when needed, screening for and clearing bacteria carried in the nose.
Your own contribution as a patient also matters:
- Regulate your blood sugar, weight and nutrition as far as possible before surgery, and stop smoking.
- Tell your doctor about any cuts, scratches, rashes or signs of infection on the skin before surgery.
- Do not shave the surgical area yourself; the necessary preparation is done at the hospital.
- After surgery, treat sources such as dental and urinary tract infections without delay.
When Should You See a Doctor?
Time matters in a prosthesis infection; seeking help early improves the chance of saving the implant.
- You have new or steadily increasing pain and stiffness in your replaced joint.
- You see redness, increased warmth, swelling or drainage around the wound.
- This is accompanied by fever, chills or night sweats.
To have symptoms related to your replaced joint assessed you can contact Assoc. Prof. Serkan Sürücü, and you can also review the other conditions covered within hip and joint problems.