Total knee and hip replacements are among the most commonly performed elective surgeries, significantly improving the quality of life for many patients by relieving pain and enabling them to engage in more active lifestyles.
However, as with any surgical procedure, there are risks involved. Although rare, approximately 1 in 100 patients (or about 1%) who undergo knee or hip replacement surgery may experience an infection following the procedure.
Infections related to joint replacements can either affect the surgical wound or develop deep within the area surrounding the artificial implants, which are made of metal and plastic. These infections can arise during the hospital stay or after the patient returns home, and in some cases, they may even occur years later.
This article will explore:
- The reasons why joint replacements may become infected
- The signs and symptoms of infection
- Effective treatment options for infections
- Preventative measures to reduce the risk of infections
Description:
Infections can potentially spread to your joint replacement from other areas of the body.
Bacterial infections are the primary cause of joint replacement infections. While bacteria naturally reside in the gastrointestinal (GI) tract and on our skin, they are typically kept under control by the body’s immune system. For instance, if bacteria enter the bloodstream, the immune system responds quickly to neutralize and eliminate the invading organisms.
However, joint replacements, which are made of metal and plastic, present a unique challenge for the immune system. Metal surfaces attract bacteria, and since these implants do not receive blood flow, the immune system has difficulty detecting and responding to bacterial presence around them. As a result, bacteria may colonize the metal implants, multiply, and lead to an infection in the joint.
Even with the use of antibiotics and preventive measures, patients with infected joint replacements often require surgical intervention to effectively treat the infection.
Examples of total knee implants. Joint replacement implants are typically made of metal alloys and strong, durable plastic called polyethylene.
Cause:
A joint replacement may become infected either during surgery or any time from weeks to years after the procedure.
Bacteria typically enter the body through several common routes, including:
- Breaks or cuts in the skin
- Major dental procedures, such as tooth extractions or root canals
- Wounds from other surgical procedures
Certain individuals are more susceptible to developing infections after joint replacement surgery. Risk factors for infection include:
- Immune deficiencies (e.g., HIV or lymphoma)
- Diabetes mellitus
- Peripheral vascular disease (impaired circulation in the limbs)
- Immunosuppressive treatments (e.g., chemotherapy or corticosteroids)
- Obesity
Symptoms:
The signs and symptoms of an infected joint replacement may include:
- Increased pain or stiffness in a previously functional joint
- Swelling around the joint
- Warmth and redness near the surgical wound
- Wound drainage, which may include blood, pus, or other fluids
- Fever, chills, and night sweats
- Fatigue or general malaise
Doctor Examination:
When a joint infection is suspected, early diagnosis and appropriate treatment are crucial for preserving the implant. During your visit, your doctor will review your medical history and perform a thorough physical examination.
Tests:
- Imaging Tests: X-rays and bone scans can help determine whether an infection is present in the joint replacement implants.
- Laboratory Tests: Certain blood tests can help identify the presence of infection. In addition to routine blood work, such as a complete blood count (CBC), your surgeon may order specific tests that measure inflammation in the body, including:
- C-reactive protein (CRP)
- Erythrocyte sedimentation rate (ESR)
Although these tests do not definitively confirm an infection, elevated CRP and/or ESR levels increase suspicion of an infection. If these values are within normal ranges, an infection is unlikely.
Additionally, your doctor may sample fluid from your joint to detect signs of infection. This procedure involves using a needle to draw fluid from the hip or knee joint, which is then analyzed under a microscope for bacteria. The sample is also sent to a laboratory where it is cultured to identify bacterial or fungal growth.
The fluid is also examined for the presence of white blood cells. In a healthy joint, the fluid contains a small number of white blood cells. A high number of white blood cells, particularly neutrophils, can indicate an infection. The fluid may also be tested for specific proteins that are commonly found in the presence of infection.
Other diagnostic tools, such as Synovasure, may also be used to test the synovial fluid. This test detects a particular protein within the fluid that can help confirm the presence of an infection.
Treatment:
Nonsurgical Treatment:
In some cases, the infection may only affect the skin and soft tissues surrounding the joint, without spreading to the artificial joint itself. This type of infection is known as a “superficial infection.” If detected early, your doctor may recommend intravenous (IV) or oral antibiotics. This approach is generally effective for treating early-stage superficial infections.
Surgical Treatment:
Infections that extend beyond the superficial tissues and reach the artificial joint typically require surgical intervention.
- Debridement: For infections that are detected early (within several days of onset) or those that develop within weeks of the original surgery, a surgical washout may help eliminate the infection. This procedure, called debridement, involves removing all contaminated soft tissue and thoroughly cleaning the implant. Plastic liners or spacers may be replaced, and intravenous (IV) antibiotics are typically prescribed for about six weeks to help clear the infection.
- Staged Surgery: If the infection has been present for a longer duration—especially in cases of late infections (those occurring months to years after the joint replacement)—staged surgery is usually necessary.
The first stage of this procedure includes:
- Removal of the infected implant
- Washout of the joint and surrounding tissues
- Insertion of an antibiotic spacer
- Administration of intravenous (IV) antibiotics
An antibiotic spacer is placed in the joint to maintain its normal alignment and function while simultaneously treating the infection. It also helps to reduce discomfort and enhance mobility during the treatment process.
Spacers used in staged surgery are made from bone cement that is infused with antibiotics. These antibiotic-loaded spacers release medication into the joint and surrounding tissues, gradually helping to eliminate the infection over time.
Patients undergoing staged surgery typically require at least 6 weeks of intravenous (IV) antibiotics, and sometimes longer, before a new artificial joint can be implanted.
Orthopaedic surgeons collaborate closely with infectious disease specialists to guide the treatment process. These specialists are responsible for determining:
- The specific antibiotics to be used
- Whether the antibiotics will be delivered intravenously (through a tube inserted into the arm) or orally (taken by mouth)
- The appropriate duration of the antibiotic therapy
Additionally, they will monitor the patient’s progress through periodic blood tests to assess the effectiveness of the antibiotics.
Once the orthopaedic surgeon and the infectious disease specialist confirm that the infection has been resolved—typically after at least 6 weeks of treatment—the patient will be considered for a new total hip or knee implant, a procedure known as revision surgery. This is the second stage of treatment for joint replacement infection.
During revision surgery, the surgeon will:
- Remove the antibiotic spacer
- Perform another washout of the joint
- Implant new total knee or hip components
