Overview
Infectious bursitis of the knee, particularly involving the pes anserinus bursae, is a relatively uncommon condition that can present with significant clinical manifestations despite its rarity. The pes anserinus bursae, located at the medial aspect of the knee where the tendons of the tibialis anterior, pes anserinus longus, and pes anserinus brevis converge, can become inflamed and infected due to trauma, repetitive stress, or direct inoculation. This form of bursitis can mimic other knee pathologies, making accurate diagnosis crucial for effective management. While typically less visible on imaging studies, giant cases can present as palpable masses, necessitating thorough clinical evaluation and appropriate diagnostic workup.
Clinical Presentation
Infectious bursitis of the knee, especially when involving the pes anserinus bursae, often presents with localized symptoms that can vary in severity. Patients commonly report pain and tenderness over the medial aspect of the knee, particularly around the pes anserinus region. This pain is typically exacerbated by activities that compress or stress the bursa, such as prolonged sitting or kneeling. Swelling and warmth may be evident, reflecting the inflammatory process. In more severe or chronic cases, as highlighted by a case report of a giant pes anserinus bursitis [PMID:34301386], a significant soft tissue mass can develop, making the clinical visibility pronounced despite the typically subtle nature of bursae involvement.
The differential diagnosis for pes anserinus bursitis includes other causes of medial knee pain such as meniscal tears, collateral ligament injuries, tendinopathies (e.g., pes anserinus tendinitis), and septic arthritis. Distinguishing features often include the absence of joint effusion in bursitis compared to septic arthritis, and the localized nature of symptoms in bursitis versus more diffuse joint involvement in arthritis. A thorough history focusing on potential trauma, repetitive motions, or recent infections can guide clinical suspicion towards bursitis. Physical examination should meticulously assess for tenderness, swelling, and range of motion limitations, aiding in differentiating infectious bursitis from other knee pathologies.
Diagnosis
Diagnosing infectious bursitis of the knee, particularly involving the pes anserinus bursae, can be challenging due to the subtlety of imaging findings. Typically, ultrasound and MRI may not clearly visualize the bursa itself, often only showing minor fluid collections or indirect signs of inflammation such as thickening of adjacent tendons or soft tissue edema [PMID:34301386]. Therefore, clinical suspicion remains a cornerstone of diagnosis, complemented by targeted diagnostic procedures. Aspiration of the bursa fluid is crucial, with analysis for white blood cell count, Gram stain, and culture essential for confirming infection. Elevated white blood cell counts and positive cultures are definitive indicators of septic bursitis.
In cases where imaging fails to provide clear evidence, surgical exploration or diagnostic arthroscopy might be considered, especially in suspected giant or complex bursitis presentations. These invasive methods can directly visualize the bursa and obtain tissue samples for histopathological examination, which can be pivotal in confirming the diagnosis when non-invasive methods fall short. It is important to rule out other knee pathologies through comprehensive imaging and clinical correlation, ensuring that the focus remains on the bursa as the primary source of symptoms.
Management
The management of infectious bursitis of the knee, particularly in the context of a giant pes anserinus bursitis, requires a multifaceted approach tailored to the severity and extent of the infection. Initial management typically involves conservative measures aimed at reducing inflammation and pain. Rest and immobilization of the affected limb can help alleviate symptoms and prevent further irritation. Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly prescribed to manage pain and reduce inflammation, with dosing often starting at 250-500 mg of ibuprofen or naproxen twice daily, adjusted based on patient response and tolerance.
In cases where conservative measures are insufficient or the bursitis is confirmed to be infected, antibiotic therapy is essential. The choice of antibiotics should be guided by the results of bursa fluid cultures and sensitivities, aiming for broad coverage initially if cultures are pending. Commonly used antibiotics include first-generation cephalosporins (e.g., cefazolin 2 grams intravenously every 8 hours) or clindamycin plus a beta-lactamase inhibitor (e.g., clindamycin 600 mg intravenously every 6 hours plus gentamicin 2.5 mg/kg every 8 hours). Duration of antibiotic therapy typically ranges from 2 to 4 weeks, depending on the response to treatment and the severity of infection.
For persistent or recurrent infections, or in cases of giant bursitis as highlighted by specific case reports [PMID:34301386], surgical intervention may be necessary. Surgical options include bursectomy, where the infected bursa is excised, often combined with thorough irrigation of the surrounding tissues. Postoperatively, continued antibiotic therapy may be required, tailored to the surgical findings and culture results. Monitoring for signs of recurrence or complications such as cellulitis or deeper soft tissue infections is crucial, with follow-up visits scheduled at intervals of 1-2 weeks initially, tapering based on clinical improvement.
Key Recommendations
References
1 Corominas H, Balius R, Estrada-Alarcón P, Reina D, Moya P, Videla M. Giant pes anserinus bursitis: A rare soft tissue mass of the medial knee. Reumatologia clinica 2021. link
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