What causes olecranon bursitis (inflammation of the fluid-filled sac on the elbow)?

Causes of Olecranon Bursitis (Knot on Elbow with Pain)

Olecranon bursitis occurs from three primary mechanisms: repetitive trauma/pressure, infection (septic bursitis in approximately one-third of cases), or inflammatory conditions, with trauma being capable of triggering both septic and non-septic forms. 1

Primary Etiologies

Traumatic/Mechanical Causes

• Repetitive minor trauma from external pressure is the most common cause, earning pseudonyms like "student's elbow" or "miner's elbow" based on occupational patterns 2
• Direct trauma such as falls or direct blows to the elbow can cause acute inflammation of the bursal cavity 3
• Overuse injuries from repetitive activities that place pressure on the posterior elbow lead to chronic irritation 4

Infectious Causes (Septic Bursitis)

• Bacterial infection accounts for approximately one-third of all olecranon bursitis cases 1
• Trauma can serve as a portal of entry for bacteria, making both traumatic injury AND infection possible simultaneously 1
• The most common organism is Staphylococcus aureus, though rare pathogens like Prototheca wickerhamii can occur in immunocompromised patients 5
• Clinical distinction is critical: both septic and non-septic bursitis can present with local erythema, making aspiration with microscopy, Gram staining, and culture mandatory when infection is suspected 1

Inflammatory/Rheumatologic Causes

• Gout can cause olecranon bursitis through crystal deposition 4
• Other rheumatological conditions occasionally trigger bursal inflammation 1
• Laboratory analysis of aspirated bursal fluid is necessary to differentiate gout from infection 4

Critical Diagnostic Approach

Initial Assessment

• Aspiration should be performed in ALL cases to differentiate septic from non-septic causes 1
• Clinical features help separate the two, but overlap exists—particularly with erythema present in both forms 1
• If doubt remains after aspiration, microscopy, Gram staining, and culture definitively resolve the diagnosis 1

Imaging Considerations

• Radiographs are the appropriate initial imaging to exclude fractures, heterotopic ossification, or other bony pathology 6
• Ultrasound can measure bursal volume and assess fluid characteristics 7
• Advanced imaging (MRI) is rarely needed unless there is concern for associated tendon or ligament pathology 6

Common Pitfalls to Avoid

• Do not assume non-infectious based on appearance alone: erythema occurs in both septic and non-septic bursitis, making aspiration essential rather than optional 1
• Do not miss immunocompromised states: patients with HIV/AIDS or other immunosuppression can harbor unusual organisms requiring different treatment approaches 5
• Do not overlook occupational/activity patterns: identifying the repetitive trauma source is essential for preventing recurrence 2
• Do not delay aspiration: waiting to aspirate when infection is possible can lead to prolonged morbidity, as septic bursitis recovery can take months even with appropriate treatment 1