handlebar palsy

• Guyon's canal syndrome
  
  
  • ulnar nerve can become compressed at the wrist within Guyon's canal
    • typical risk factors for Guyon's canal syndrome are:
      • overuse of the wrist (especially flexion, rotation and gripping -weightlifters) or
      • constant direct pressure over the canal itself (cyclists with dropped handlebars, crutch use) or
      • mechanical impingement (wrist arthritis, fractured hamate classically seen when golfers strike the ground and not the ball! and rarely due to thrombosis of the ulnar artery)
    • ulnar nerve provides sensation to the medial 1 1/2 digits and power to the hypothenar eminence
    • depending upon exactly where within the Guyon's canal the ulnar nerve is damaged presentation may involve pure sensory disturbance, pure motor disturbance, or a combination of both. Tinel's test (tapping the finger over the Guyon's canal) will often precipitate clinical symptoms
      • classified into three types:
        • Type I
          • proximal compression in Guyon's canal leads to motor weakness in all of the intrinsic muscles of the hand which are innervated by the ulnar nerve
          • also sensory loss in the territory of the hand served by the ulnar nerve
        • Type II
          • most common type of Guyon's canal syndrome, and is caused by compression of the ulnar nerve at the lower wrist
          • causes symptoms associated with Type I, however the sensory branch to the dorsal part of the hand and the motor supply to the muscles of the base of the palm are unaffected
            • Type II thus involves an impairment in motor function of the hand, with sensory innervation unaffected
        • Type III
          • least common type of Guyon's canal syndrome, and is caused by compression of the superficial branch of the ulnar nerve at the distal portion of Guyon's canal
          • results in a loss of sensation from the cutaneous territory of the hand which is served by the ulnar nerve. There is no motor function impairment
            
            
  • management:
    • diagnosis should be made clinically but can be confirmed with nerve conduction studies (NCS) (a negative NCS does not completely rule out compression)
      • differential diagnoses are:
        • cubital tunnel syndrome (entrapment of ulnar nerve at the elbow)
        • lower pole brachial plexus disease
        • T1 radiculopathy
          
          
    • if the motor supply is affected the patient may have wasting of the small muscles of the hand and the hypothenar eminence along with a positive Froment's and Wartenberg's test
      
      
    • conservative treatment involves identification of the cause and appropriate intervention, i.e. padded gloves or handlebar adjustment for cyclists, ergonomic advice and physiotherapy in overuse syndromes, and appropriate management of any underlying arthritis or fracture
      • local hydrocortisone injections can be beneficial, avoiding the close-lying ulna artery
        
        
    • surgical treatment
      • in resistant cases or cases presenting with hypothenar muscle-wasting referral should be made for surgical decompression
        • to relieve tension in the volar carpal ligament which forms the roof of Guyon's canal, thereby reducing compression on the ulnar nerve
      • urgent surgical referral should be made where the ulna nerve is compressed due to a fractured hamate or to the rare thrombosis of the ulnar artery

Reference:

• (1) Arthritis Research UK (April 2013). The upper limb in primary care. Part 2: Wrist, hand. Hands On 2(7).