What is the recommended imaging protocol for diagnosing pronator teres syndrome?

Imaging Protocol for Pronator Teres Syndrome

Ultrasound is the recommended first-line imaging modality for diagnosing pronator teres syndrome, with MRI reserved for cases where ultrasound is inconclusive or to exclude alternative diagnoses. 1, 2

Primary Imaging Approach

Ultrasound (First-Line)

• Dynamic ultrasound examination is essential to visualize median nerve compression between the ulnar and humeral heads of the pronator teres muscle during pronation and supination movements 1, 2
• Ultrasound can directly demonstrate the site of nerve compression and guide therapeutic interventions such as hydrodissection 2
• The examination should focus on the proximal forearm, approximately 6 cm distal to the medial epicondyle, where compression typically occurs 3
• Look for median nerve enlargement, flattening, or altered echogenicity at the compression site 1

MRI (Confirmatory/Alternative)

• MRI should be obtained when ultrasound findings are equivocal or to confirm the diagnosis before surgical intervention 1
• MRI can visualize the median nerve anatomy and surrounding soft tissue structures with high resolution 1
• Non-contrast MRI of the forearm is sufficient for evaluating nerve compression and excluding mass lesions or other structural abnormalities 1

Electrodiagnostic Testing (Complementary)

• Electroneuromyography (EMG/NCS) is critical for confirming the diagnosis and should be performed alongside imaging 1, 4
• Key findings include delayed proximal motor latency of the median nerve and diminished motor nerve conduction velocity in the proximal forearm segment 4
• Distal motor latency and sensory latency should remain normal, distinguishing this from carpal tunnel syndrome 4

Clinical Integration

Physical Examination Findings to Correlate

• Tenderness over the pronator teres muscle in the proximal forearm 4
• Paresthesias in the median nerve distribution (thumb, index, middle, and radial half of ring finger) 1, 4
• Weakness of flexor pollicis longus, abductor pollicis brevis, and opponens pollicis 4
• Symptoms that worsen with resisted pronation or repetitive forearm movements 1
• The flexor digitorum test should be performed to exclude compression at other sites 3

Diagnostic Algorithm

1. Start with clinical examination focusing on provocative maneuvers (resisted pronation, direct palpation over pronator teres) 1, 4
2. Perform dynamic ultrasound as the initial imaging study to visualize nerve compression during movement 1, 2
3. Obtain EMG/NCS to confirm median nerve dysfunction at the proximal forearm level 1, 4
4. Add MRI if ultrasound is technically limited, findings are unclear, or surgical planning is needed 1

Critical Pitfalls to Avoid

• Do not rely on imaging alone—pronator teres syndrome requires correlation of clinical symptoms, physical examination findings, electrodiagnostic studies, and imaging 1
• Distinguish from carpal tunnel syndrome, which is 201 times more common and can coexist with pronator teres syndrome 4
• Ensure dynamic assessment during ultrasound examination, as static imaging may miss compression that occurs only with specific forearm positions 2
• Consider bilateral evaluation as the condition can be bilateral in some patients 4