(Kiosk 2) Ulnar Nerve Entrapment at the Arcade of Struthers

Case Diagnosis: 32 year old right hand dominant female with left 4th, 5th digit numbness secondary to ulnar nerve entrapment at the Arcade of Struthers.

Case Description or Program Description: The patient received a bilateral upper extremity nerve conduction study to evaluate for focal mononeuropathy of left ulnar nerve. The patient had been experiencing progressively worsening left 4th, 5th digit numbness and weakness without history of trauma or relevant surgery. Nerve conduction study demonstrated normal values of bilateral median motor and sensory nerves, normal values of right ulnar motor and sensory, while left ulnar studies were significant for normal distal latency, reduced compound muscle action potential amplitudes proximal to elbow with normal values distally and slowed conduction velocity across the elbow and slightly slowed through the forearm. While inching proximally, the signal of the ulnar nerve significantly dropped at about 4 centimeters above the medial epicondyle. Left ulnar sensory study demonstrated delayed onset latency, reduced sensory nerve action potential. MRI of left elbow and arm demonstrated thickened ulnar nerve in between the Arcade of Struthers and cubital tunnel.

Setting: Ambulatory Care Center

Assessment/Results: Based on electrodiagnostic evaluation and imaging, the Arcade of Struthers is likely responsible for this patient’s proximal ulnar nerve entrapment. Plans for ultrasound guided perineural corticosteroid injection around the site of entrapment to follow. The nerve conduction study of the region near the cubital tunnel suggests that this was indeed not the site of entrapment even though it is a common site of entrapment.

Discussion (relevance): There is significant controversy regarding the presence of the Arcade of Struthers and thus further debate regarding the involvement of it in proximal ulnar nerve entrapment. This case demonstrates electrodiagnostic evidence and imaging evidence to support the involvement of the Arcade of Struthers in proximal ulnar nerve entrapment.

Conclusions: Based on electrodiagnostic evaluation and sensitive imaging, the Arcade of Struthers is likely responsible for this patient’s proximal ulnar nerve entrapment furthering supporting evidence of the existence of this structure as well as a potential site of entrapment.