Ulnar nerve

Origin
Ulnar nerve comes from the medial cord of the brachial plexus (C8-T1)
Course
Arm lies posteromedial to brachial artery in anterior compartment of upper 1/2 arm pierces medial IM septum at the arcade of Struthers ~ 8cm from medial epicondyle and lies medial to the triceps the arcade of Struthers is an aponeurotic band extending from the medial IM septum to the medial head of the triceps Elbow runs behind medial epicondyle with superior ulnar collateral artery Cubital tunnel roof - Osbourne’s ligament proximally (extension of deep forearm fascia between heads of FCU) and FCU aponeurosis distally floor - posterior and transverse bands of MCL and elbow joint capsule sends small sensory branch to elbow that can be sacrificed Forearm enters forearm between 2 heads (humeral and ulnar heads) of FCU runs between FCU and FDP Wrist the ulnar nerve and artery pass superficial to the transverse carpal ligament bifurcates into sensory and deep motor branches in Guyon's canal roof - volar carpal ligament floor - transverse carpal ligament, hypothenar muscles ulnar border - pisiform and pisohamate ligament, abductor digiti minimi muscle belly radial border - hook of hamate
Innervation
Motor Innervation forearm FCU FDP ring and small thenar adductor pollicis deep head of flexor pollicis brevis (FPB) fingers interossei (dorsal & palmar) 3rd & 4th lumbricals hypothenar muscles abductor digiti minimi opponens digiti minimi flexor digiti minimi Sensory Innervation sensory branches of ulnar nerve dorsal cutaneous branch palmar cutaneous branch superficial terminal branches
Clinical Conditions
Cubital Tunnel Syndrome sites of compression (proximal to distal) medial intermuscular septum most proximal site, 8cm proximal to medial epicondyle Arcade of Struthers medial epicondyle (osteophytes) cubital tunnel retinaculum (Osborne's ligament) anconeus epitrochlearis muscle replaces Osborne's ligament in 11% of population, causing static compression aponeurosis of the two heads of the FCU (arcuate ligament) often continuous with Osbourne's ligament deep flexor/pronator aponeurosis most distal site, 4 cm distal to medial epicondyle elbow flexion reduce cubital tunnel volume because FCU aponeurosis tenses Osborne's ligament becomes taught MCL bulges into cubital tunnel the internal anatomy of the ulnar nerve explains the predominance of hand symptoms in cubital tunnel syndrome fibers to FCU and FDP are central and hand intrinsic fibers are peripheral Ulnar tunnel syndrome compression in Guyon’s Canal no involvement of dorsal cutaneous nerve since it branches before canal no involvement of FDP of 4^th & 5^th and FCU causes ganglia most common cause (from triquetrohamate joint, 30-50%) other causes include mass, trauma (fracture of distal radius or ulna, hook of hamate), muscle anomaly, ulnar artery aneurysm or thrombosis compression sites Zone 1: proximal to bifurcation, both motor & sensory symptoms caused by hook of hamate fracture and ganglia Zone 2: deep motor branch, motor symptoms only caused by hook of hamate fracture and ganglia Zone 3: superficial sensory branch, sensory symptoms only caused by ulnar artery aneurysm or thrombosis

Ulnar Nerve: What Should I Do? - John J. Fernandez, MD (CSMS #79, 2018)

Ulnar Nerve Issues in Throwers - John E. Conway, MD (BSM #27, 2016)

CUBITAL TUNNEL SYNDROME - Ulnar neuropathy USMLE step 1 lecture , clinical anatomy