Nerve Entrapments — Cubital Tunnel Syndrome

Cubital tunnel syndrome is the second most common peripheral nerve entrapment neuropathy after carpal tunnel syndrome, involving compression of the ulnar nerve at the elbow. The ulnar nerve is vulnerable at the cubital tunnel — the fibro-osseous canal posterior to the medial epicondyle — where it is tethered, relatively superficial, and subjected to significant tension and compression, particularly during elbow flexion. Understanding the anatomy, sites of compression, clinical grading, and surgical options is essential for the orthopaedic surgeon.

• Anatomy of the cubital tunnel: the tunnel is bounded by the medial epicondyle anteriorly, the olecranon posterolaterally, the medial collateral ligament floor, and the arcuate ligament of Osborne (Osborne`s band — the retinaculum between the two heads of flexor carpi ulnaris) as its roof; the ulnar nerve enters the tunnel from the posterior compartment of the arm, traverses the tunnel, then passes between the two heads of FCU into the forearm
• Multiple potential sites of ulnar nerve compression at the elbow: (1) medial intermuscular septum (arcade of Struthers — ligamentous condensation 8 cm proximal to medial epicondyle); (2) medial epicondyle (groove — the most common site); (3) Osborne`s band (arcuate ligament of FCU heads); (4) deep flexor-pronator aponeurosis; (5) anconeus epitrochlearis (accessory muscle present in approximately 10% — compresses the nerve in the cubital tunnel)
• Incidence: second most common entrapment neuropathy; prevalence approximately 25 per 100,000 per year; male predominance; risk factors include prolonged elbow flexion, occupational vibration, cubitus valgus deformity, prior elbow fracture (especially medial epicondyle, lateral condyle with tardy ulnar nerve palsy), direct compression (leaning on elbow), diabetes

• During elbow flexion, the volume of the cubital tunnel decreases by approximately 50% — this increases intraneural pressure significantly; prolonged elbow flexion (during sleep, telephone use, driving) is the most common provocative factor
• Tardy ulnar nerve palsy: delayed ulnar nerve palsy occurring years after a childhood elbow fracture (most commonly a lateral condyle fracture malunion or Posadas fracture); the progressive cubitus valgus deformity that develops after lateral condyle non-union or malunion increases the tension on the ulnar nerve as it courses around the medial epicondyle; can present decades after the original injury; ulnar nerve transposition is the surgical treatment
• Ulnar nerve subluxation: the nerve subluxes anteriorly over the medial epicondyle during elbow flexion in approximately 16% of the population; repeated subluxation causes intraneural fibrosis and may require surgery

• Symptoms: medial elbow pain; tingling and numbness in the ulnar 1.5 digits (little and ring fingers — ulnar digital distribution); weakness of grip and pinch; clumsy hand; symptoms worse at night and with prolonged elbow flexion
• McGowan classification (modified Dellon):

• Ulnar claw hand: ring and little finger clawing (MCP hyperextension + IP flexion) due to loss of ulnar lumbrical and interosseous function; the ulnar two digits are affected because only the radial two lumbricals are innervated by the median nerve; the clawing is less severe in high (proximal) ulnar nerve lesions because FDP 4/5 (also ulnar innervated) is also weak, reducing IP flexion — "ulnar paradox" or intrinsic minus hand
• Froment sign: patient grips a piece of paper between the thumb and the lateral border of the index finger; the examiner pulls the paper; positive = thumb IPJ flexes (using FPL — median nerve) to compensate for weak adductor pollicis (ulnar nerve); tests the integrity of adductor pollicis
• Elbow flexion test (Wadsworth): maximum elbow flexion held for 60 seconds; positive if ulnar nerve symptoms reproduced in the ring and little fingers; sensitivity approximately 75%; combined with direct pressure over the cubital tunnel (elbow flexion + compression test) increases sensitivity
• Tinel sign at the cubital tunnel: percussion over the cubital tunnel reproduces paraesthesia into the ulnar digits; sensitivity approximately 70%

• EMG and nerve conduction studies (NCS): gold standard investigation; slowing of motor conduction velocity across the elbow (<50 m/s or >10 m/s slower across the elbow than forearm segment); reduced SNAP amplitude for ulnar sensory; EMG shows denervation in the intrinsic muscles (first dorsal interosseous most sensitive) and FDP 4/5; helps confirm diagnosis, grade severity, localise the lesion, and guide surgical planning; a normal NCS does not exclude mild clinical cubital tunnel syndrome
• Plain radiographs: AP and lateral elbow; assess for cubitus valgus (angle >15° = abnormal), previous fracture malunion (lateral condyle), osteophytes, loose bodies
• MRI: identifies extrinsic causes (ganglion, tumour, anconeus epitrochlearis); shows nerve signal change and calibre; rarely required for straightforward clinical diagnosis
• USS: dynamic assessment of ulnar nerve subluxation; nerve cross-sectional area; identifies accessory muscles (anconeus epitrochlearis); useful and cost-effective adjunct

• Activity modification: avoid prolonged elbow flexion; avoid direct elbow pressure (no leaning on the elbow); use telephone headset instead of handset; modify workstation
• Night extension splinting: an elbow pad or extension splint worn at night maintains the elbow at approximately 45° of flexion, preventing prolonged extreme flexion during sleep; significantly reduces nocturnal symptoms; the single most important non-operative intervention for cubital tunnel syndrome; a folded pillow around the elbow is an alternative; compliance-dependent
• NSAIDs: limited evidence for nerve compression specifically; may help for associated medial epicondylitis component
• Physiotherapy: nerve gliding exercises; postural correction; limited evidence but low risk
• Non-operative management for 3–6 months in Grade I–II; Grade III or progressive neurological deficit should be offered early surgical intervention

• Simple decompression (in situ release): division of Osborne`s band and the arcuate ligament of FCU without moving the nerve; preserves the blood supply of the nerve; minimally invasive; can be performed endoscopically; most evidence supports simple decompression as equivalent to anterior transposition for most patients; technically simpler with lower risk of complication; preferred for mild-moderate disease without subluxation or significant cubitus valgus
• Anterior transposition: the ulnar nerve is mobilised and moved anteriorly to the medial epicondyle — into the subcutaneous tissue (subcutaneous transposition), into the intramuscular plane (intramuscular), or under the flexor-pronator muscle mass (submuscular); anterior transposition is preferred over simple decompression when: significant cubitus valgus is present; nerve subluxates over the medial epicondyle; revision surgery after failed decompression; medial epicondyle osteophytes; underlying structural elbow pathology
• Medial epicondylectomy: partial or complete removal of the medial epicondyle; allows the nerve to lie anteriorly without tension; less commonly performed; risk of medial instability (MCL takes partial origin from the medial epicondyle) if too aggressive
• Submuscular transposition: most distal nerve protection; the nerve is placed beneath the flexor-pronator origin; requires 4–6 weeks immobilisation post-operatively; preferred in cases requiring the most protection (high-demand overhead athletes, revision cases, cases with significant scarring)

• Ulnar paradox: in a high ulnar nerve lesion (above the elbow), FDP 4/5 is also denervated (ulnar nerve innervates FDP 4/5 in the forearm proximal to the wrist); loss of FDP 4/5 means the ring and little fingers cannot flex the IP joints actively; without IP flexion, the claw deformity is paradoxically less pronounced than in a low lesion — a "balanced" intrinsic-minus hand; this is the ulnar paradox — higher lesions produce less obvious clawing than lower lesions despite being more severe neurologically
• Tardy ulnar nerve palsy after lateral condyle fracture: progressive cubitus valgus develops when the lateral condyle fails to unite or malunites; the valgus deformity increases the tension on the ulnar nerve around the medial epicondyle over years to decades; management is anterior transposition of the ulnar nerve; the underlying valgus deformity may also need corrective osteotomy in severe cases; a common exam scenario — recognise the history of childhood elbow injury + progressive ulnar nerve symptoms in adulthood
• Anconeus epitrochlearis: an anomalous accessory muscle arising from the olecranon and inserting on the medial epicondyle; present in approximately 10% of the population; bridges the cubital tunnel, producing direct compression of the ulnar nerve; identified on MRI or USS; excision at the time of decompression provides excellent relief; important to recognise pre-operatively as simple Osborne`s band release will be insufficient
• Outcomes of surgery: sensory recovery typically precedes motor recovery; Grade I–II patients have best outcomes (approximately 90% good/excellent after decompression); Grade III patients have less predictable motor recovery — once significant axonal loss and intrinsic wasting have occurred, recovery is incomplete; grade at the time of surgery is the most important prognostic factor

• Second most common entrapment neuropathy after CTS; ulnar nerve at cubital tunnel; Osborne`s band most common compression point
• Compression sites from proximal to distal: arcade of Struthers → medial epicondyle groove → Osborne`s band (FCU heads) → deep flexor-pronator aponeurosis
• McGowan Grade III: intrinsic wasting + clawing + Froment positive + persistent paraesthesia; surgery; prognosis less predictable at this stage
• Ulnar claw: ring and little fingers (MCP hyperextension + IP flexion); ulnar lumbricals and interossei lost; radial two digits spared (median innervated lumbricals)
• Ulnar paradox: high lesion (above elbow) = FDP 4/5 also lost = less pronounced clawing than low lesion; paradoxically more severe neurologically but less deformity
• Froment sign: FPL compensates for weak adductor pollicis during key pinch; IPJ flexion of thumb on pulling paper = positive
• Night extension splinting: most important non-operative intervention; prevents prolonged nocturnal elbow flexion
• Simple decompression vs transposition: equivalent outcomes for most patients; transposition preferred for cubitus valgus, subluxating nerve, revision, or structural pathology
• Tardy ulnar nerve palsy: childhood lateral condyle fracture → progressive cubitus valgus → delayed ulnar neuropathy; anterior transposition treatment
• Anconeus epitrochlearis: accessory muscle (10%); direct cubital tunnel compression; excise at surgery; recognise on USS/MRI pre-operatively