Does an 85-year-old man with severe right knee osteoarthritis, fever, tachycardia, and elevated white blood cell count warrant a joint tap or orthopedic consultation?

From the Guidelines

This case warrants both a joint tap (arthrocentesis) and an orthopedics consult due to the high suspicion of septic arthritis, which is a medical emergency requiring prompt diagnosis and treatment. The 85-year-old man presents with concerning features suggestive of septic arthritis, including worsening knee pain and swelling over several weeks, fever, tachycardia, elevated white blood cell count (13.9), and large joint effusion on x-ray, despite his underlying osteoarthritis 1. A joint tap should be performed immediately to obtain synovial fluid for cell count, Gram stain, culture, and crystal analysis to differentiate between septic arthritis, crystal arthropathy (gout or pseudogout), or an inflammatory flare of his osteoarthritis.

The recent study by 1 highlights the importance of joint aspiration in diagnosing joint infection, with a sensitivity and specificity of 100% in some cases. The study also notes that a negative aspiration does not necessarily rule out infection, and repeat aspirations may be necessary if clinical suspicion remains high.

While waiting for the tap results, empiric antibiotics covering common pathogens like Staphylococcus aureus should be considered, typically vancomycin 15-20 mg/kg IV or cefazolin 2g IV every 8 hours. The orthopedic consultation is necessary because if septic arthritis is confirmed, the patient may require surgical irrigation and debridement in addition to antibiotics.

Key points to consider in this case include:

• The patient's age and comorbidities increase his risk for poor outcomes if septic arthritis is not promptly addressed, making urgent evaluation crucial despite the chronic nature of his underlying joint disease.
• The combination of an abnormal sedimentation rate and C-reactive protein (CRP) seems to provide the best combination of sensitivity and specificity for diagnosing prosthetic joint infection, although this patient does not have a prosthetic joint 1.
• A diagnostic arthrocentesis should be performed in all patients with suspected acute septic arthritis unless the diagnosis is evident clinically and surgery is planned and antimicrobials can be safely withheld prior to surgery 1.
• Blood cultures for aerobic and anaerobic organisms should be obtained if fever is present, as in this case 1.

Overall, the patient's presentation and laboratory results suggest a high likelihood of septic arthritis, and prompt diagnosis and treatment are essential to prevent long-term damage and improve outcomes.

From the Research

Patient Presentation

The patient is an 85-year-old man with a history of chronic severe right knee osteoarthritis, presenting with worsening right knee pain and swelling over several weeks. He is febrile, tachycardic, and mildly hypoxic, with a white count of 13.9. The chest x-ray is clear, but the right knee x-ray shows advanced osteoarthrosis, a large joint effusion, and no gross soft tissue swelling.

Diagnostic Considerations

Given the patient's symptoms and laboratory results, there is a concern for a possible infectious process, such as septic arthritis. The presence of a large joint effusion and elevated white count suggests the need for further diagnostic evaluation, including joint aspiration and analysis of the synovial fluid 2.

Joint Aspiration and Analysis

Joint aspiration is a crucial diagnostic tool in this scenario, as it can help confirm the presence of an infection and guide antibiotic therapy 3, 4. The analysis of the synovial fluid can provide valuable information, including the cell count and differential, which can help diagnose periprosthetic infection 2. A study published in 2008 found that a synovial fluid leukocyte count of >1100 cells/10^(-3)cm^3 and a neutrophil percentage of >64% were highly sensitive and specific for the diagnosis of periprosthetic infection 2.

Orthopedic Consultation

Given the patient's complex presentation and the need for further diagnostic evaluation, an orthopedic consultation is warranted. The orthopedic specialist can help determine the best course of action, including the need for joint aspiration, antibiotic therapy, and possible surgical intervention.

Key Points

• Joint aspiration and analysis of the synovial fluid are essential diagnostic tools in this scenario 3, 4, 2.
• The presence of a large joint effusion and elevated white count suggests the need for further diagnostic evaluation 2.
• An orthopedic consultation is warranted to determine the best course of action 5.
• The patient's symptoms and laboratory results suggest a possible infectious process, such as septic arthritis, which requires prompt diagnosis and treatment 2.