What are the signs and symptoms of knee bursitis in a patient with a history of rheumatoid arthritis or recent trauma to the knee?

Signs of Knee Bursitis

Knee bursitis presents with localized pain, swelling, and tenderness over the affected bursa, with prepatellar and pes anserine bursae being most commonly involved. 1

Clinical Presentation

Cardinal Signs

• Localized swelling over the bursa, which may be visible and palpable 1, 2
• Point tenderness directly over the affected bursa upon palpation 1, 2
• Pain with pressure (e.g., kneeling on prepatellar bursa or pressure from shoes in retrocalcaneal bursitis) 3, 2
• Warmth and erythema in the overlying skin, particularly in acute or septic cases 2

Location-Specific Findings

Prepatellar bursitis:

• Swelling anterior to the patella 1, 2
• Pain with direct kneeling 2
• Visible fluid collection over the kneecap 2

Pes anserine bursitis:

• Tenderness over the medial proximal tibia 1
• Pain exacerbated by valgus stress 4
• Swelling along the medial knee and proximal tibia 4

Infrapatellar bursitis:

• Swelling below the patella 1, 2
• Pain with kneeling or direct pressure 2

Suprapatellar bursitis:

• Detected more readily by imaging than clinical examination 5
• May present as joint effusion clinically 5

Key Distinguishing Features in Rheumatoid Arthritis Context

In patients with rheumatoid arthritis, imaging detects bursitis more frequently than clinical examination alone, with ultrasound showing 1.7-fold higher detection rate for suprapatellar bursitis compared to clinical assessment 5. The presence of bursitis may indicate active inflammatory disease requiring adjustment of disease-modifying therapy.

Post-Trauma Considerations

Following knee trauma, hemorrhagic bursitis may develop, presenting with:

• Rapid onset of swelling 1, 2
• Fluctuant mass on palpation 2
• Ecchymosis in surrounding tissues 2
• History of direct blow or fall onto the knee 2

Red Flags for Septic Bursitis

Septic bursitis requires immediate recognition and presents with:

• Acute onset of warmth, erythema, and swelling 2
• Fever (though may be absent) 2
• Severe tenderness disproportionate to swelling 2
• Overlying skin changes or cellulitis 2
• History of penetrating trauma or immunosuppression 2

Functional Limitations

• Decreased range of motion may occur, particularly with suprapatellar or deep bursitis 4
• Pain with specific movements depending on bursa location (e.g., knee flexion with infrapatellar bursitis) 1
• Difficulty with occupational activities requiring kneeling or prolonged knee flexion 6

Common Diagnostic Pitfalls

Bursitis frequently mimics other knee pathologies, making careful localization essential 1. Key distinctions include:

• Versus arthritis: Bursitis produces localized tenderness over the bursa rather than diffuse joint line tenderness 1, 7
• Versus tendinitis: Pain is over the bursa rather than along the tendon course 7
• Versus joint effusion: True bursitis has discrete swelling outside the joint capsule, though imaging may be needed to distinguish suprapatellar bursitis from joint effusion 5
• Versus cellulitis: Ultrasound can definitively distinguish between these conditions 2

Imaging Findings

While clinical diagnosis is primary, ultrasound is the most effective imaging modality when confirmation is needed 3:

• Hyperechoic foci with posterior acoustic shadowing indicate calcific bursitis 3
• Fluid collection within the bursa 3
• Synovial thickening in chronic cases 3
• High-frequency ultrasound (≥10 MHz) detects small effusions missed on examination 8, 9