What is the best initial test to diagnose a biceps tendon rupture?

Best Initial Test for Biceps Tendon Rupture

Clinical examination should be the first diagnostic step, with plain radiographs followed by MRI without contrast as the imaging sequence of choice when imaging is needed to confirm the diagnosis or distinguish partial from complete tears. 1, 2, 3

Diagnostic Algorithm

Step 1: Clinical Examination (Initial Assessment)

• Physical examination alone is often sufficient to diagnose complete ruptures and should include specific maneuvers 4, 5:

  • Hook test combined with biceps crease interval (BCI) measurement provides 94% sensitivity and 100% specificity for acute complete ruptures 5
  • Palpation for tendon defect in the antecubital fossa 6, 7
  • Assessment for visible/palpable proximal migration of the biceps muscle belly 6, 4
  • Biceps squeeze test 7

• For chronic complete ruptures (>1 month), weakness on active supination provides 100% sensitivity 5

• Pain on palpation of the tendon footprint provides 100% sensitivity for partial ruptures 5

Step 2: Plain Radiographs (First Imaging Study)

• Obtain plain radiographs first to rule out associated fractures or bony abnormalities 1, 2, 3
• May show hypertrophic bone formation at the radial tuberosity in chronic cases 6
• Not diagnostic for tendon rupture itself but excludes other pathology 4

Step 3: MRI Without Contrast (Definitive Imaging)

• MRI is the most accurate imaging modality with 86.4% accuracy for complete distal biceps tears, compared to only 45.5% for ultrasound 1, 2, 8
• MRI demonstrates superior sensitivity (76%) and specificity (50%) compared to ultrasound (62.5% and 20% respectively) 9, 8
• The FABS (flexion-abduction-supination) view is specifically recommended for optimal visualization of the distal biceps tendon 1, 2, 3
• MRI is particularly crucial for distinguishing partial from complete tears, which directly impacts surgical decision-making 1, 2, 4, 8

Alternative: Ultrasound (Limited Role)

• Ultrasound can be considered only when MRI is contraindicated 1, 3
• Major limitation: ultrasound has significantly inferior accuracy (45.5% vs 86.4%) and poor specificity (20%) for detecting complete tears 9, 8
• Ultrasound performs equally poorly as MRI for partial tears (66.7% accuracy for both), but this is still suboptimal 9, 8
• The medial imaging approach is preferred if ultrasound is used, with better interreader agreement 9, 1

Critical Pitfalls to Avoid

• Never rely solely on ultrasound for diagnosis - it misses over half of complete tears and has very poor specificity 9, 1, 2, 8
• Failing to distinguish partial from complete tears leads to inappropriate treatment plans - this distinction requires MRI, not clinical exam alone 1, 2, 3
• Do not skip plain radiographs - associated fractures or avulsion injuries must be identified 1, 2, 3
• In acute complete ruptures with classic clinical findings (positive Hook test + BCI), imaging may be obtained primarily for surgical planning rather than diagnosis 5

Key Clinical Context

• Distal biceps ruptures typically occur in middle-aged men (40-60 years) in the dominant arm after eccentric loading 6, 7
• Complete ruptures benefit from early surgical repair, making accurate diagnosis time-sensitive 6, 7, 4
• Partial ruptures can often be managed conservatively, making the distinction clinically critical 7, 4, 5