Median nerve syndromes: pronator teres syndrome

The median nerve pierces the two heads of the pt (pronator teres) before passing under it. Trauma, fracture, muscle hypertrophy or an anomalous band connecting the pt to the tendon arch of the flexor digitorum sublimis can injure the nerve here. Also tenosynovitis, muscle hemorrhage, tear, postop scarring, anomalous median artery, or increased forearm compartment pressure can be related.

Clinically,  pain and tenderness appears over the pronator teres, is fatiguaibile, with the pain radiating occassionally to the shoulder. Weakness of the flexor pollicis and apb, and preserved pronation. Sensory changes over the thenar eminence help to make the diagnosis. EMG/NCS distal studies are normal with slowing in the wrist.

A different entrapment at the site of the ligament of Struthers affects the nerve near the lower humerus. The difference clinically is that here, pronator teres is affected unlike the pt syndrome in which pt is spared. Compression of the brachial artery with full extension of the arm obliterates the radial pulse.

Differentiate from CTS with Tinel's over site of entrapment, absent Phalen's sign, rare nocturnal exacerbation, weak mm over forearm worse with pronation, elbow flexion or contraction of the superficial flexor of second digit. Consider CTS, plexopathy, other median neuropathy syndromes, or radiculopathy.