What may cause knee bursitis to become inflamed?

Causes of Knee Bursitis Inflammation

The most common causes of knee bursitis inflammation are direct trauma, chronic microtrauma, infection, and inflammatory disorders such as gout or rheumatoid arthritis. 1

Traumatic Causes

• Acute trauma - Direct impact to the knee can cause immediate inflammation of the bursa, often accompanied by hemorrhage into the bursal sac 1
• Chronic microtrauma - Repetitive pressure or friction on the knee, such as from frequent kneeling (in prepatellar bursitis) or excessive walking/running (in infrapatellar bursitis) 1, 2
• Overuse injuries - Repetitive activities that stress the knee joint can lead to bursal inflammation, particularly in athletes or workers with occupational knee stress 3

Infectious Causes

• Septic bursitis - Bacterial infection of the bursa, most commonly caused by Staphylococcus aureus, which may enter through breaks in the skin or via bloodstream 1
• Cellulitis extension - Infection of surrounding soft tissues can spread to the bursa 1

Inflammatory/Systemic Causes

• Gout - Deposition of monosodium urate crystals in the bursa can trigger acute inflammation 4, 1
• Rheumatoid arthritis - Autoimmune inflammation can affect the bursae around the knee joint 1, 5
• Calcium pyrophosphate deposition disease (pseudogout) - Crystal deposition can cause bursal inflammation 5
• Spondyloarthropathies - Conditions like ankylosing spondylitis can affect bursal tissues 3

Degenerative Causes

• Osteoarthritis - Degenerative joint disease can be associated with bursitis, particularly in the medial collateral ligament bursa 6
• Biomechanical abnormalities - Altered knee mechanics due to structural issues can increase pressure on bursae 2

Less Common Causes

• Haglund's deformity - A bony enlargement on the back of the heel that can irritate the retrocalcaneal bursa 5
• Juvenile idiopathic arthritis - Can cause bursitis in pediatric patients 3
• Metabolic factors - Obesity and metabolic syndrome increase the risk of inflammatory conditions including bursitis 5, 4

Diagnostic Considerations

• Ultrasound imaging is highly effective for distinguishing bursitis from other conditions like cellulitis and for detecting fluid accumulation 5, 3
• MRI can confirm the diagnosis and help identify associated conditions like tendinopathy 3
• When infection is suspected, bursal aspiration with fluid analysis (including Gram stain, crystal analysis, glucose measurement, cell count, and culture) is essential 1

Treatment Implications

• Treatment should be directed at the underlying cause of the bursitis 5, 1
• For traumatic bursitis: rest, ice, elevation, and analgesics are recommended 1
• For infectious bursitis: appropriate antibiotics targeting Staphylococcus aureus 1
• For inflammatory bursitis: treatment of the underlying condition (e.g., gout management) 4
• Corticosteroid injections may be helpful for non-infectious bursitis but should be used cautiously, especially near tendons like the Achilles 2
• Viscosupplementation with hyaluronic acid injections may be beneficial for bursitis associated with degenerative conditions 7

Understanding the specific cause of knee bursitis inflammation is crucial for appropriate management and prevention of recurrence.