Knee replacement surgery significantly improves mobility and alleviates pain, particularly for end-stage knee arthritis. While most surgeries are successful, infections, though uncommon, can occur. Understanding their signs, diagnosis, and treatment is important.
Recognizing the Signs
Knee replacement infections can manifest with various symptoms, appearing soon after surgery or much later. Acute infections, occurring shortly after surgery, may present with persistent local pain, redness, swelling, warmth, and fluid drainage. Systemic signs like fever and chills can accompany these.
Chronic infections, emerging months or years post-surgery, often present subtly. Patients might experience increased knee pain, stiffness, or inability to bear weight. A draining sinus tract, a tunnel from the infection to the skin, is a clear sign of periprosthetic joint infection. Any new or worsening symptoms in a replaced knee should prompt immediate medical evaluation.
Diagnosing the Infection
Confirming a knee replacement infection involves a comprehensive medical evaluation. This begins with a physical examination of the knee, assessing swelling, warmth, redness, and tenderness. Blood tests check for inflammatory markers like C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR), usually elevated. White blood cell count may also be assessed.
Imaging studies provide insights into the joint’s condition. Plain X-rays are usually the initial step, though they may not always show early signs. More advanced techniques, such as MRI, CT scans, and nuclear medicine studies (e.g., bone scintigraphy or labeled white blood cell scans), offer detailed views of the prosthesis and surrounding tissues. These scans can identify bone marrow edema, soft tissue collections, or changes around the implant suggestive of infection.
The most definitive diagnostic step involves aspirating fluid directly from the knee joint. This synovial fluid is sent for laboratory analysis, including cell count, differential count (neutrophil percentage), and culture to identify the microorganism causing the infection. This analysis guides targeted antibiotic therapy.
Treatment Strategies
Treating a knee replacement infection often requires combined medical and surgical interventions. The approach depends on factors like bacteria type, patient health, and infection duration. Antibiotic therapy is fundamental, often starting with intravenous antibiotics for several weeks, followed by oral antibiotics.
Surgical options vary based on infection severity and nature. One common procedure is debridement, antibiotics, and implant retention (DAIR). This involves surgically cleaning the infected joint, removing infected tissue, exchanging modular components, and administering antibiotics while retaining the original implant. DAIR is typically considered for acute infections, especially when the implant is well-fixed and identified early.
For established or chronic infections, or when DAIR is not suitable, revision arthroplasty procedures are often necessary. A one-stage exchange arthroplasty involves removing the infected prosthesis, thoroughly debriding the joint, and immediately implanting a new prosthesis during the same procedure. This option is generally reserved for healthy patients with known, susceptible organisms and good soft tissue conditions.
The two-stage exchange arthroplasty is a standard approach for chronic knee replacement infections, especially for resistant bacteria. The first stage involves removing the infected implant and associated cement, thoroughly cleaning the joint, and placing an antibiotic-loaded cement spacer. This spacer maintains joint space and delivers high concentrations of antibiotics to the infected area. After intravenous antibiotics (typically 6-12 weeks) and confirmation that the infection has cleared, a second surgery removes the spacer and implants a new, permanent knee prosthesis.
In severe, uncontrolled cases where other treatments have failed, drastic measures may be considered. Arthrodesis, or fusion of the knee joint, permanently joins the thigh and shin bones, eliminating the joint but providing a stable, pain-free limb. Amputation is a last resort, typically reserved for life-threatening infections or when limb salvage is not possible.
Outlook and Recovery
Recovery from a knee replacement infection and its treatment can be prolonged and challenging. Patients typically require extensive physical therapy and rehabilitation to regain strength, mobility, and function. Adherence to a prescribed rehabilitation program is important for optimizing outcomes.
Long-term follow-up is necessary to monitor for recurrent infection. While successful eradication is often achieved, recurrence is possible, particularly in complex cases. The impact on mobility and quality of life varies depending on infection severity and treatment required. Despite challenges, successful treatment allows many individuals to return to daily activities.