What diagnostic tests are used to diagnose bursitis?

Diagnostic Tests for Bursitis

The diagnosis of bursitis is primarily clinical, but when imaging is needed, ultrasound is the first-line and most effective diagnostic test, as it can directly visualize bursal fluid, inflammation, and calcifications while distinguishing bursitis from other conditions. 1, 2

Initial Diagnostic Approach

Clinical Diagnosis

• Most cases of bursitis can be diagnosed based on clinical presentation alone, focusing on localized pain, swelling, and tenderness over the affected bursa 3, 4
• Key clinical features include: tenderness to palpation over the bursa, pain aggravated by pressure or movement, and visible swelling in superficial bursae (prepatellar, olecranon) 2, 3
• Critical distinction: Determine whether septic bursitis is present, as this fundamentally changes management 3

When Imaging Is Indicated

• Imaging may not be necessary if the clinical diagnosis is clear, but should be pursued when the diagnosis is uncertain or when distinguishing from other conditions like cellulitis, arthritis, or tendinitis 1, 3
• Specific indications for imaging: suspected septic bursitis, chronic or recurrent symptoms, failure to respond to conservative treatment, or when calcific bursitis is suspected 2, 3

Imaging Modalities in Order of Preference

Ultrasound (First-Line Imaging)

Ultrasound is the preferred initial imaging modality for suspected bursitis because it provides real-time, dynamic assessment without radiation exposure 1, 2

Technical specifications:

• High-frequency ultrasound (10 MHz and above) is highly sensitive for detecting bursal pathology 2
• Can be performed at the bedside and is particularly useful for guiding aspiration procedures 1

What ultrasound detects:

• Bursal fluid collections and distension appear as anechoic or hypoechoic areas 1, 5
• Calcifications within the bursa appear as hyperechoic foci with posterior acoustic shadowing 2
• Associated inflammation: synovial thickening, hyperemia on Doppler imaging 2, 5
• Helps distinguish bursitis from cellulitis, which is a critical clinical differentiation 3
• Can identify specific bursae: trochanteric, retrocalcaneal, prepatellar, olecranon, iliopsoas, and pes anserine 1, 5

Dynamic assessment advantage:

• Real-time evaluation during movement helps differentiate bursal pathology from tendinopathy or other conditions 2

Plain Radiographs (Complementary Role)

Radiographs are not sensitive for diagnosing acute bursitis but can detect calcifications and rule out other pathology 1

When to obtain radiographs:

• Should be obtained first in chronic hip pain to screen for arthritis, fractures, or bone tumors before proceeding to advanced imaging 1
• Can detect larger calcifications appearing as rounded, amorphous opacities adjacent to bony prominences 2
• Less sensitive than ultrasound for smaller calcium deposits and cannot visualize bursal fluid 2

MRI (When Ultrasound Is Insufficient)

MRI is highly sensitive and specific for detecting bursitis when ultrasound is equivocal or when evaluating deep bursae 1

Specific indications:

• Deep bursae that are difficult to access with ultrasound: iliopsoas bursa, subiliacus bursa 1
• When evaluating surrounding structures: to assess for associated tendinopathy, muscle tears, or other soft tissue pathology 1
• Trochanteric bursitis: MRI can assess the trochanteric bursa, gluteus medius and minimus tendons, and abductor muscle integrity 1
• IV contrast is rarely needed for diagnosing bursitis 1

MRI findings in bursitis:

• Fluid collections, bursal distension, capsular thickening 1
• Can differentiate joint fluid from synovitis when combined with IV gadolinium or ultrasound 1

CT Scan (Limited Role)

CT is less sensitive than ultrasound and MRI for soft tissue evaluation but can detect calcifications 1, 2

Specific uses:

• More sensitive than radiography for detecting calcifications but less commonly used as first-line imaging 2
• Dual-energy CT can differentiate calcium deposits from other crystal depositions (e.g., gout) 2
• Generally not recommended as a primary diagnostic tool for bursitis 1

Diagnostic Aspiration and Laboratory Testing

When to Aspirate

Bursal aspiration should be performed when septic bursitis is suspected 3

Indications for aspiration:

• Signs of infection: fever, warmth, erythema, systemic symptoms 3
• Immunocompromised patients with bursal swelling 3
• Failure to respond to conservative treatment 3

Aspiration should be image-guided (ultrasound or fluoroscopy) to ensure accurate needle placement 1

Bursal Fluid Analysis

When infection is suspected, aspirated fluid must be examined comprehensively 3

Required tests on aspirated fluid:

• Gram stain and culture to identify bacterial pathogens (Staphylococcus aureus most common) 3
• Crystal analysis to detect gout or pseudogout 1, 3
• Cell count and differential (elevated WBC suggests infection) 3
• Glucose measurement (low glucose suggests infection) 3

Blood Testing

Blood tests help distinguish infectious from non-infectious bursitis 3

Recommended laboratory studies:

• White blood cell count and inflammatory markers (ESR, CRP) are elevated in septic bursitis 3
• These tests support but do not confirm the diagnosis of septic bursitis 3

Diagnostic Algorithm by Location

Trochanteric Bursitis

• Ultrasound is the preferred initial test for evaluating the trochanteric bursa and abductor tendons 1
• MRI is indicated when ultrasound is equivocal or when evaluating for gluteus medius/minimus tears 1
• Diagnostic injection of the trochanteric bursa with anesthetic can confirm the diagnosis if imaging is inconclusive 1

Retrocalcaneal Bursitis

• High-frequency ultrasound is highly effective for visualizing the retrocalcaneal bursa 2, 4
• Radiographs can detect associated Achilles tendon calcifications 2
• Avoid steroid injection into the retrocalcaneal bursa due to risk of Achilles tendon rupture 4

Prepatellar and Olecranon Bursitis

• Clinical diagnosis is usually sufficient for superficial bursae 3, 4
• Ultrasound is indicated when distinguishing from cellulitis or when septic bursitis is suspected 3, 5
• Aspiration is mandatory if infection cannot be excluded clinically 3

Iliopsoas Bursitis

• MRI is more sensitive than ultrasound for deep iliopsoas bursa evaluation 1
• Ultrasound can be used for guiding diagnostic/therapeutic injections 1

Common Pitfalls and How to Avoid Them

Failing to distinguish tendon calcification from bursal calcification:

• Use ultrasound to precisely localize calcifications within the bursa versus adjacent tendons, as treatment approaches differ 2

Missing small calcifications on plain radiographs:

• Always use ultrasound when calcific bursitis is suspected, as radiographs miss smaller deposits 2

Confusing bursitis with cellulitis:

• Ultrasound definitively distinguishes between bursal fluid collection and soft tissue inflammation of cellulitis 3

Aspirating chronic microtraumatic bursitis unnecessarily:

• Avoid aspiration of non-infected chronic bursitis due to risk of introducing infection (iatrogenic septic bursitis) 3

Overlooking septic bursitis:

• Always aspirate when infection is suspected, as delayed treatment of septic bursitis leads to significant morbidity 3

Misinterpreting trochanteric bursitis for other hip pathology:

• Differentiate between isolated bursitis and associated abductor tendon tears using ultrasound or MRI, as management differs 1