Residency · Residency · Physical Medicine Rehabilitation

Ulnar Neuropathy at the Elbow

Anatomy

Ulnar Nerve Course at the Elbow

The ulnar nerve passes posterior to the medial epicondyle in the ulnar groove (retrocondylar groove). It then enters the cubital tunnel, formed by the medial epicondyle, olecranon, and the arcuate ligament (Osborne ligament) as the roof. The floor of the cubital tunnel is the medial collateral ligament and joint capsule. The nerve passes between the two heads of the flexor carpi ulnaris (FCU) distally. The cubital tunnel is the most common site of compression; the retrocondylar groove is the second most common.

Potential Compression Sites

Arcade of Struthers: musculofascial band approximately 8 cm proximal to the medial epicondyle (uncommon). Medial intermuscular septum: as the nerve pierces from anterior to posterior compartment. Retrocondylar groove: bony groove posterior to the medial epicondyle. Cubital tunnel (Osborne ligament): the most common compression site.

Between the two heads of FCU: as the nerve exits the cubital tunnel. Anconeus epitrochlearis: anomalous muscle overlying the ulnar groove (present in ~10% of individuals).

Ulnar Nerve Innervation

Motor (forearm): FCU and FDP to digits 4-5. Motor (hand): hypothenar muscles (ADM, ODM, FDM), interossei (all), 3rd and 4th lumbricals, adductor pollicis, deep head of FPB. Sensory: dorsal ulnar cutaneous branch (dorsal hand/digits 4-5), palmar cutaneous branch, and digital nerves to digit 5 and ulnar half of digit 4.

Dynamic Factors

Elbow flexion narrows the cubital tunnel by 55% and increases intraneural pressure 6-fold. The arcuate ligament tightens with flexion, compressing the nerve. Ulnar nerve subluxation over the medial epicondyle occurs in 16% of the population. Repetitive elbow flexion-extension, direct pressure ("cell phone elbow"), and prolonged positioning during surgery are risk factors.

<image>Anatomical illustration of the ulnar nerve at the elbow showing the retrocondylar groove, cubital tunnel with the Osborne ligament forming the roof, passage between the two heads of flexor carpi ulnaris, and potential compression points along the nerve course</image>

Clinical Evaluation

Symptoms

Numbness and tingling in the ring and small fingers (ulnar 1.5 digits). Symptoms often exacerbated by sustained elbow flexion (phone use, sleeping with elbow bent). Weakness of grip and pinch strength. Clumsiness with fine motor tasks (buttoning, typing). Medial elbow pain (may or may not be present).

Physical Examination

Sensory testing: decreased sensation in ulnar 1.5 digits (palmar and dorsal). Tinel sign at elbow: tapping behind the medial epicondyle reproduces paresthesias. Elbow flexion test: sustained maximum elbow flexion with wrist extension for 60 seconds. Froment sign: compensatory FPL flexion (median-innervated) during key pinch due to adductor pollicis weakness.

Wartenberg sign: small finger abduction at rest due to unopposed EDM (radial nerve) with weak 4th palmar interosseous. Ulnar claw hand: hyperextension at MCP joints and flexion at IP joints of digits 4-5 (more prominent with lower lesions -- "ulnar paradox"). Intrinsic atrophy: first dorsal interosseous wasting, hypothenar wasting. Jeanne sign: hyperextension of thumb MCP during pinch (weak adductor pollicis and FPB). Assess for ulnar nerve subluxation with elbow flexion-extension.

Electrodiagnostic Evaluation

Ulnar Motor NCS

Record from ADM (E1 over motor point, E2 over 5th MCP joint). Stimulate at wrist, below elbow, and above elbow. Also record from FDI for improved sensitivity. Across-elbow conduction velocity: <50 m/s is abnormal; <40 m/s is definite.

Elbow should be flexed to 70-90 degrees during testing to standardize the nerve path length. Distance measured from below-elbow to above-elbow stimulation sites (minimum 10 cm).

Localization Criteria (AANEM Consensus)

Conduction velocity across the elbow <50 m/s. >10 m/s slowing across the elbow compared to the forearm segment. Amplitude drop >20% across the elbow (conduction block). Abnormality of only 1 criterion is suggestive; 2 or more criteria provide definite localization.

Short Segment Incremental Stimulation (Inching)

Stimulate at 1-2 cm intervals across the elbow (typically 6-8 stimulation points). Record from ADM or FDI. Identify the precise point of focal slowing or conduction block. Latency change >0.4 ms per cm segment is abnormal.

Can pinpoint compression to the retrocondylar groove versus cubital tunnel versus FCU heads. Technically demanding but highly valuable for surgical planning.

Ulnar Sensory NCS

Digit 5 to wrist (antidromic or orthodromic). Reduced SNAP amplitude or absent SNAP indicates sensory axonal loss. Comparison with the opposite side is helpful (side-to-side amplitude difference >50% is significant). Dorsal ulnar cutaneous nerve (DUCN) sensory study: branches proximal to the wrist.

DUCN SNAP is NORMAL in ulnar neuropathy at the wrist (Guyon canal) but ABNORMAL in elbow lesion. Key differentiating study between elbow and wrist ulnar neuropathy.

Medial Antebrachial Cutaneous Nerve (MABC) Study

MABC branches from the medial cord of the brachial plexus, not the ulnar nerve. MABC SNAP should be NORMAL in ulnar neuropathy at the elbow. If MABC SNAP is abnormal, consider medial cord or lower trunk plexopathy rather than isolated ulnar neuropathy.

<image>Diagram of the short segment incremental stimulation (inching) technique across the elbow showing stimulation points at 2 cm intervals from below to above the medial epicondyle, with corresponding CMAP tracings demonstrating focal latency change and amplitude drop at the point of compression</image>

Needle EMG Findings

FDI (first dorsal interosseous): most sensitive muscle for ulnar neuropathy; examine first. ADM (abductor digiti minimi): frequently involved but may be spared in mild cases. FCU: involvement suggests lesion at or proximal to the elbow (FCU branch exits early). FDP digits 4-5: involvement localizes proximal to mid-forearm.

Ulnar-innervated thenar muscles (adductor pollicis, deep head FPB): may be affected. Non-ulnar C8-T1 muscles (APB, EIP, FPL): should be NORMAL; abnormalities suggest radiculopathy or plexopathy. Cervical paraspinals: examine to exclude C8-T1 radiculopathy.

Differential Diagnosis

C8-T1 Radiculopathy

SNAP is preserved (preganglionic lesion). Non-ulnar C8-T1 muscles are affected (APB, EIP, FPL). Paraspinal fibrillations may be present. No focal slowing across the elbow.

Lower Trunk/Medial Cord Plexopathy

MABC SNAP is abnormal (distinguishes from ulnar neuropathy). Ulnar and median C8-T1 muscles affected. Low CMAP amplitudes without focal elbow slowing. Consider neurogenic thoracic outlet syndrome (Gilliatt-Sumner hand).

Ulnar Neuropathy at the Wrist (Guyon Canal)

DUCN SNAP is normal (branches proximal to Guyon canal). FCU and FDP strength and EMG are normal. Motor, sensory, or mixed involvement depending on zone of compression. Causes: ganglion cysts, hook of hamate fracture, handlebar palsy.

Hirayama Disease (Monomelic Amyotrophy)

Predominantly affects young males. Asymmetric hand weakness and atrophy (C7-T1 distribution). NCS may show low CMAP amplitudes without focal slowing. Neck flexion MRI shows forward displacement of cervical dura.

Management

Conservative Management

Elbow padding and nighttime splinting (elbow in 30-45 degrees of flexion). Activity modification: avoid sustained elbow flexion and direct pressure on the elbow. Ergonomic adjustments (keyboard tray height, phone use). Most effective for mild cases without axonal loss.

Surgical Management

Simple decompression (in situ release): release of Osborne ligament and FCU fascia; less tissue disruption. Anterior transposition: subcutaneous, intramuscular, or submuscular; moves nerve anterior to the medial epicondyle. Medial epicondylectomy: partial removal of the medial epicondyle. Surgical indications: failure of conservative management, progressive weakness, moderate-to-severe electrodiagnostic abnormalities, axonal loss on EMG. Controversy: simple decompression versus anterior transposition; meta-analyses show similar outcomes for most cases.

Clinical Pearls

FDI is more sensitive than ADM for detecting ulnar neuropathy at the elbow; always include it in the EMG screen. The "ulnar paradox": more distal lesions produce MORE prominent clawing (because FDP to digits 4-5 is intact, maintaining IP flexion). Always check the DUCN sensory study to differentiate elbow from wrist lesions. An abnormal MABC SNAP should raise concern for plexopathy rather than isolated ulnar neuropathy.

Elbow position during NCS matters: standardize at 70-90 degrees of flexion for accurate across-elbow measurements. Martin-Gruber anastomosis can confuse ulnar motor studies by appearing to show conduction block; suspect when wrist CMAP is larger than expected. Bilateral ulnar neuropathy should prompt evaluation for systemic causes (diabetes, alcoholism, HNPP). Subluxation of the ulnar nerve does not necessarily cause neuropathy; many asymptomatic individuals have subluxation.

References

• AANEM Practice Parameter: Electrodiagnosis of Ulnar Neuropathy at the Elbow. Muscle Nerve. 1999;22(3):408-411.
• Campbell WW. Ulnar Neuropathy at the Elbow. Muscle Nerve. 2000;23(4):450-452.
• Preston DC, Shapiro BE. Electromyography and Neuromuscular Disorders. 4th Edition. Elsevier. 2021.
• Caliandro P, et al. Ulnar Neuropathy at the Elbow: An Update on Electrodiagnosis. Clin Neurophysiol. 2020;131(2):469-477.
• Bartels RH, et al. Surgery for Ulnar Neuropathy at the Elbow. Cochrane Database Syst Rev. 2012.

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