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Updated: May 22 2023

Ulnar Tunnel Syndrome

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  •  Summary
    • Ulnar Tunnel Syndrome is a compressive neuropathy of the ulnar nerve at the level of the wrist (Guyon's canal), most commonly due to a ganglion cyst.
    • Diagnosis can be made clinically with paresthesias of the small and ring finger with intrinsic weakness with a Tinel's sign over Guyon's canal.
    • Treatment involves a course of conservative management with splinting, and surgical decompression in the presence of a compressive lesion (i.e ganglion) or continued symptoms. 
  • Epidemology
    • Incidence
      • less common than cubital tunnel syndrome
    • Risk factors
      • cyclists (also known as handlebar palsy)
  • Etiology
    • 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
        • Radial border
        • Hook of hamate
        • Zones of Guyon's canal
        • Zone
        • Location
        • 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 3 and 4)
        • 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
    • Cubital tunnel syndrome 
      • compared to ulnar 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
  • Diagnosis
    • Clinical and EMG/NCS
      • diagnosis confirmed with history, physical exam and EMG/NCS 
        • MRI studies used to confirm presense of compressive lesion (i.e ganglion)
  • 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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