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https://upload.orthobullets.com/topic/6022/images/CT cross section labeled_moved.jpg
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 Introduction
  • Ulnar nerve compression neuropathy caused by direct compression in Guyon's canal
    • also known as handlebar palsy (seen in cyclists) 
  • Pathoanatomy
    • causes of compression include
      • ganglion cyst (80% of nontraumatic causes)
      • lipoma
      • repetitive trauma
      • ulnar artery thrombosis or aneurysm
      • hook of hamate fracture or nonunion
      • pisiform dislocation
      • inflammatory arthritis
      • fibrous band, muscle or bony anomaly
      • congenital bands
      • palmaris brevis hypertrophy
      • idiopathic 
 Anatomy
  • Guyon’s canal
    • course
      • is approximately 4 cm long
      • begins at the proximal extent of the transverse carpal ligament and ends at the aponeurotic arch of the hypothenar muscles
    • contents
      • ulnar nerve bifurcates into the superficial sensory and deep motor branches
    • boundaries and zones (see table below)
Boundaries of Guyon's canal 
Floor Transverse carpal ligament, hypothenar muscles
Roof Volar carpal ligament
Ulnar border Pisiform and pisohamate ligament, abductor digiti minimi muscle belly
Radial border Hook of hamate
Zones of Guyon's canal  
Location Common Causes of Compression Symptoms
Zone 1 Proximal to bifurcation of the nerve Ganglia and hook of hamate fractures Mixed motor and sensory
Zone 2 Surrounds deep motor branch Ganglia and hook of hamate fractures Motor only
Zone 3 Surrounds superficial sensory branch Ulnar artery thrombosis or aneurysm Sensory only
  • Deep branch of the ulnar nerve
    • innervates all of the interosseous muscles and the 3rd and 4th lumbricals.
    • Innervates the hypothenar muscles, the adductor pollicis, and the medial head (deep) of the flexor pollicis brevis (FPB)
 Classification
  • Presentation varies based on location of compression within Guyon's canal and may be
    • Motor only
    • Sensory only
    • Mixed Motor & Sensory
 Presentation
  • Presentation varies based on location of compression within Guyon's canal and may be
    • pure motor
    • pure sensory
    • mixed motor and sensory
  • Symptoms
    • pain and paresthesias in ulnar 1-1/2 digits
    • weakness to intrinsics, ring and small finger digital flexion or thumb adduction
  • Physical exam
    • inspection & palpation
      • clawing of ring and little fingers
        • caused from loss of intrinsics flexing the MCPs and extending the IP joints
      • Allen test  
        • helps diagnose ulnar artery thrombosis
    • neurovascular exam
      • ulnar nerve palsy results in paralysis of the intrinsic muscles (adductor pollicis, deep head FPB, interossei, and lumbricals 4 and 5)
      • weakened grasp
        • from loss of MP joint flexion power
      • weak pinch
        • from loss of thumb adduction (as much as 70% of pinch strength is lost)
      • Froment sign 
        • IP flexion compensating for loss of thumb adduction when attempting to hold a piece of paper
        • loss of MCP flexion and adduction by adductor pollicis (ulnar n.)
        • compensatory IP hyperflexion by FPL (AIN)
      • Jeane's sign 
        • a compensatory thumb MCP hyperextension and thumb adduction by EPL (radial n.)
        • compensates for loss of IP extension and thumb adduction by adductor pollicis (ulna n.)
      • Wartenberg sign
        • abduction posturing of the little finger
 Imaging
  • Radiographs  
    • useful to evaluate hook of hamate fractures
  • CT scan  
    • useful to evaluate hook of hamate fractures
  • MRI
    • useful to evaluate for a ganglion cysts
    • a gradient echo MRI will also show an ulnar artery aneurysm 
  • Doppler US or arteriogram  
    • useful to diagnosis ulnar artery thrombosis and aneurysm
 Studies
  • NCS and EMG
    • helpful in establishing diagnosis and prognosis
    • threshold for diagnosis
      • conduction velocity <50 m/sec across elbow
      • low amplitudes of sensory nerve action potentials and compound muscle action potentials
 Differential
  • How to differentiate ulnar tunnel syndrome from cubital tunnel syndrome
    • cubital tunnel demonstrates
      • less clawing
      • sensory deficit to dorsum of the hand
      • motor deficit to ulnar-innervated extrinsic muscles
      • Tinel sign at the elbow
      • positive elbow flexion test
 Treatment
  • Nonoperative
    • activity modification, NSAIDS and splinting
      • indications
        •  as a first line of treatment when symptoms are mild
  • Operative  
    • local decompression
      • indications
        • severe symptoms that have failed nonoperative treatment
    • tendon transfers
      • indications
        • correction of clawed fingers
        • loss of power pinch
        • Wartenberg sign (abduction of small finger)
    • carpal tunnel release
      • indications
        • patients diagnosed with both ulnar tunnel syndrome and CTS
 Techniques
  • Local surgical decompression 
    • release hypothenar muscle origin
    • decompress ganglion cysts 
    • resect hook of hamate
    • vascular treatment of ulnar artery thombosis
    • explore and release all three zones in Guyon's canal
  • Tendon transfers
    • correct claw fingers
      • possible grafts include ECRL, ECRB, palmaris longus
      • tendons must pass volar to transverse metacarpal ligament in order to flex the proximal phalanx
      • attach with either a two or four-tailed graft to the A2 pulley of the ring and small fingers
    • restore power pinch
      • Smith transfer using ECRB or FDS of ring finger
    • restore adduction of small finger
      • transfer ulnar insertion of EDM to A1 pulley or radial collateral ligament of the small finger
 Complications
  • Recurrence
 

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(OBQ10.132) A 72-year-old female complains of progressive weakness with grasp and key pinch in her left hand. Physical exam of the hand is significant for decreased sensation on the volar aspect of the fourth and fifth digits. Dorsal sensation throughout the hand is normal. A clinical photo displaying bilateral key pinch is shown in Figure A. What is the most likely cause of compression? Review Topic

QID: 3225
FIGURES:
1

Accessory head of the FPL

5%

(106/1929)

2

Flexor carpi ulnaris

10%

(193/1929)

3

Osborne's ligament

21%

(403/1929)

4

Ganglion within Guyon's canal

61%

(1170/1929)

5

Anconeus epitrochlearis

2%

(44/1929)

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