Ulnar nerve

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ULNAR NERVE

Anatomy
Lesions
Axilla
Elbow
Forearm
Wrist & Hand

Ulnar nerve: Anatomy

Formed by: C8 and T1 ± C7 roots
Axons pass through
- Brachial plexus: Lower trunk & Medial cord
- Ulnar groove: At elbow
- Cubital tunnel (Humeral-Ulnar aponeurosis): Distal to elbow; Under flexor carpi ulnaris
- Guyon's canal: Nerve entry into wrist; Between pisiform & hamate bones in hand
Branches: Most distal to elbow
- Forearm: Distal to cubital tunnel
  - Flexor carpi ulnaris (FCU)
  - Flexor digitorum profundus (FDP)(4th & 5th fingers)
  - Palmar cutaneous
    - Branch at wrist proximal to Guyon’s canal
    - Sensory: To proximal ulnar (medial) palm
  - Nerve of Henle: May be same as palmar cutaneous
    - Sympathetic axons (tyrosine hydroxylase positive): To ulnar artery
    - May provide sensory innervation to distal ulnar & palmar part of forearm
  - Dorsal ulnar cutaneous
    - Sensory: To dorsal 5th & ulnar side of 4th finger
    - May overlap with, or anomalously arise from: Superficial radial
- Hand: All motor
  - Palmaris brevis
  - Interossei
  - Lumbricals (3rd & 4th)
  - Flexor pollicis brevis
Anomalies
- Martin-Gruber anastomosis (10% to 44% of normals)
  - Branches from median to ulnar nerve in forearm
  - Innervate: 1st dorsal interosseus, Adductor pollicis, Abductor digiti minimi
- Riche-Cannieu anastomosis
  - Connections between deep ulnar & median nerves in hand

Ulnar nerve: Lesions

Gowers

Partial ulnar nerve lesion
Clawing of 2 medial fingers due
to weakness of lumbricals III & IV

Axilla & Upper arm: Uncommon
- Causes
  - Compression, external: Sleep; Crutches; Tourniquets
  - Compression at Arcade of Struthers: Fascial plane in medial triceps muscle
    - NOTE: Also see Ligament of Struthers with median nerve compression
  - Mass: Aneurysm of brachioaxillary artery; Schwannoma
- Clinical
  - Involvement of forearm muscles: FCU & FDP
  - Associated damage to median & ulnar nerves
Elbow
- Anatomy: Ulnar nerve passes
  - In front of the medial head of the triceps brachii & under arcade of Struthers
  - Into a bony groove on humerus (Cubital tunnel)
    - Proximal edge of roof of cubital tunnel is superficially closed by fibrous bands
    - Band extend from medial epicondyle to olecranon & perpendicular to flexor carpi ulnaris aponeurosis
    - Bands are known as: Cubital tunnel retinaculum (CTR); Osborne band
  - Around posterior side of medial epicondyle of humerus
- Causes ¹
  - General
    - 60% with anatomical lesion detected by ultrasound
    - 10% with 2 lesions
    - More common: Heavy smokers; Repetitive movements
  - Bony deformities
    - Old fractures
    - Osseus fragments
    - Osteophytes
    - Arthritis: Osteo; Rheumatoid
    - Shallow ulnar groove
      - Valgus deformity - congenital or 2^o to lateral epicondyle fracture
    - Paget's disease
  - Trauma: Acute, Chronic
    - Anesthesia
    - Covid-19: Prone positioning
    - Pressure with elbow flexed
    - Ulnar nerve often enlarged
    - Adhesions may occur
  - Soft tissue masses
    - In condylar groove or cubital tunnel
    - Articular ganglions
  - Muscle
    - Anconeus-Epitrochlearis
      - Anomalous accessory muscle; 2% of ulnar neuropathies
      - Requires surgical decompression of nerve
    - Triceps
      - Medial head
      - May enter groove during elbow flexion
  - Ulnar nerve prolapse: 29% of cases
    - Nerve rolls out of ulnar groove
      - Subluxation: Ulnar nerve passes on top of medial epicondyle of humerus at any degree of flexion
      - Luxation: Ulnar nerve luxates over medial epicondyle of humerus at any degree of flexion
    - Predisposes to repetitive trauma
  - Systemic disorders
  - Idiopathic
    - ? Entrapped in ulnar groove or cubital tunnel
- Clinical features
  - Pain: Maximal at elbow
  - Paresthesias & Sensory loss: Ulnar sensory distribution
    - Paresthesias: Evoked by Tinel's: Light tapping over elbow
    - Sensory loss: Medial hand; Dorsal ulnar cutaneous nerve may be spared
  - Weakness
    - Ulnar-innervated hand muscles weak: Especially 1st dorsal interosseus
    - Wartenberg sign: 5th digit more abducted than on normal hand
    - Froment sign: Pinch of thumb & index finger
      - Flexor pollicis longus substitutes for Adductor policis
      - Thumb flexes abnormally with pinch
    - Variation
      - Forearm muscles relatively spared
      - Involvement may vary among fascicles: Some muscles spared
        
        FCU (Spared most) > FDP > ADM > 1st DI (Spared least often)
- NCV testing
  - Ulnar SNAP (Digit 5) & CMAP (ADM) amplitudes: Small
  - Conduction velocity across elbow: Slowing (> 11 M/s)
  - False negative results
    - Elevated body mass index: Perform Short-segment incremental studies (SSISs)
- External link
Forearm
- Causes
  - Trauma
  - Hematoma in forearm muscles: Hemophiliacs
  - Dialysis shunts: Ischemia
Wrist & Hand
- General
  - Less common than ulnar lesion at elbow
  - Spared
    - Sensory of medial dorsal hand & fingers
    - Distal flexors of ring & little fingers
- 4 ulnar lesion sites
  - Most common lesions: Pure motor
    - Hook of hamate
    - Distal to Guyon's canal
  - Guyon's canal
    - Anatomy: Proximal canal lesion
      - Proximal: Pisiform bone
      - Distal: Hook of hamate
      - Floor: Transverse carpal ligament & Hamate + Triquetrum bones
      - Nerve in canal
        
        Enters at: Distal wrist crease
        
        Divides into: Superficial sensory & Deep palmar motor branches
    - Clinical
      - Sensory loss
        
        Volar 5th & Medial 4th digits
        
        Spared
        
        Dorsal medial hand & fingers: Innervated by dorsal ulnar cutaneous
        
        Proximal ulnar palm: Palmar cutaneous sensory branch is superficial to Guyon's canal
      - Weakness
        
        Common: All ulnar hand muscles
        
        Finger abduction
        
        Extension of ring & little finger
        
        Variant: Spared abductor digiti minimi (ADM)
    - Causes
      - Mass: Ganglion, Lipoma, Synovial cyst (35%)
      - External pressure: Cyclist's Handlebar
      - Aberrant Muscle (Abductor digiti minimi)
      - Ulnar Artery Thrombosis or Aneurism (Hypothenar Hammer Syndrome)
  - Distal to Guyon's canal
    - Anatomy: Proximal deep palmar motor lesion
    - Clinical
      - Weakness
        
        Common: All ulnar hand muscles
        
        Variant: Spared abductor digiti minimi (ADM)
      - Sensation: Normal
    - Causes
      - External pressure
      - Compression: Ligament
      - Tumor
  - Hook of hamate
    - Anatomy: Distal deep palmar motor lesion
    - Clinical
      - Motor: Spares hypothenar eminence
        
        Palmaris brevis sign: Preserved hypothenar skin wrinkling during abduction of little finger
      - Sensation: Normal
      - May be callous on hypothenar eminence at compression site
    - Causes
      - External pressure: Biking; Hand tools
      - Compression: Ligament
      - Ganglion
  - Superficial terminal branch
    - Clinical
      - Sensory loss
        
        Volar 5th & Medial 4th digits
        
        Spared: Dorsal medial hand & fingers
      - Strength: Normal
      - NCV: Reduced SNAP to 5th digit
    - Causes
      - Fracture of hook of hamate (ununited)
      - Ulnar artery aneurysm
Shoulder: External link

Go to innervation of upper extremity muscles
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References
1. Clin Exp Rheumatol 2010;28:63-67

4/25/2018