A 26-year-old man presents to the clinic for evaluation of numbness and tingling of his right ring and little fingers bilaterally for 3 days. The patient is an avid cyclist, and he states the symptoms began the day after he went on a 50-mile bike ride. He has no past medical history and takes no medications. Family history is significant for father with late-onset type 1 diabetes. He does not drink alcohol, smoke cigarettes, or use illicit drugs. He is in a monogamous relationship with his wife of 3 years. He complains of constant “pins and needles” in the little finger and medial aspect of the ring finger bilaterally. He does not recall any specific injury and denies any pain in the upper extremities. Physical examination shows full range of motion of the upper extremities and the fingers, and there is focal no tenderness or evidence of muscle atrophy. Tinel sign at the elbow and Phalen test are negative.
Given the patient’s most likely diagnosis, which of the following anatomical structures is involved in the pathogenesis of this patient’s symptoms?
E) Volar carpal ligament
This patient likely has Guyon canal syndrome (also known as “handlebar palsy,” which is a relatively rare compression of the ulnar nerve as it traverses Guyon’s canal at the wrist level. The anatomic boundaries include the volar carpal ligament as the roof; the transverse carpal ligament as the floor (this ligament continues as a single anatomic structure to become the roof of the carpal tunnel); pisiform, pisohamate ligament, and abductor digiti minimi as the ulnar boundary; and the hook of the hamate as the radial boundary.
Symptoms can be mixed motor/sensory or isolated sensory depending on whether the compression occurs proximal to the bifurcation of the sensory branch. Symptoms include paresthesias and intrinsic hand muscle weakness. Chronic compression can result in atrophy and weakness of the adductor pollicis muscle resulting in a positive Froment sign (the patient is asked to make a strong pinch between the thumb and index finger and grip a piece of paper between the thumb and index finger; weakness of the abductor pollicis causes the interphalangeal joint of the thumb to go into a hyperflexed position) on physical examination. Initial treatment includes activity modification and NSAIDS. Surgical release is reserved for refractory cases.
Answer choice A: Arcade of Struthers, is incorrect. The arcade of Struthers in an anatomical structure overlying the ulnar nerve at the elbow level that has been implicated in cubital tunnel syndrome. This patient has a negative Tinel sign at the elbow and no symptoms in the forearm, making the diagnosis of cubital tunnel syndrome less likely.
Answer choice B: Flexor retinaculum, is incorrect. The flexor retinaculum is a superficial ligamentous structure overlying the carpal tunnel. This patients’ symptoms follow an ulnar nerve distribution.
Answer choice C: Medial epicondyle of the humerus, is incorrect. The ulnar nerve traverses the posterior aspect of the humeral medial epicondyle at the elbow level and is involved in cubital tunnel syndrome.
Answer choice D: Scaphoid, is incorrect. The scaphoid (navicular) carpal bone is located on the radial side of the wrist and is not anatomically related to the ulnar nerve.
Key Learning Point
Guyon canal syndrome is a relatively uncommon nerve compression syndrome involving the ulnar nerve. The anatomical boundaries of the canal are the volar carpal ligament, transverse carpal ligament, pisiform/pisohamate ligament/abdeuctor digiti minimi, and the hook of hamate.
