Guyon's canal syndrome or ulnar nerve syndrome or handlebar palsy results from compression of the ulnar nerve as it passes through Guyon's canal (a tunnel syndrome).
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Epidemiology
The epidemiology of Guyon's canal syndrome is not well documented due to a paucity in literature 1.
Some conditions that make patients more prone to developing Guyon's canal syndrome are ganglion cysts, hook of hamate fracture and repetitive trauma (e.g. common in cyclists due to handlebar compression).
Clinical presentation
Guyon's canal contains the deep branch of the ulnar nerve, which bifurcates into a motor and a sensory branch. The symptoms depend on the involvement of the various branches of the ulnar nerve and include the following:
pain and altered sensation in the ulnar half of the 4th digit and the complete 5th digit (sensory supply of the deep branch of the ulnar nerve)
weakness in flexion, abduction and opposition of the little finger (innervation to the hypothenar muscles)
weakness in digit adduction and abduction (innervation to the interossei)
extension of the MCP and flexion of the PIP (innervation to the third and fourth lumbricals) resulting in the characteristic ulnar claw
Pathology
Three entrapment zones have been described 4:
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zone 1
proximal/within Guyon's canal but prior to ulnar nerve bifurcation
results in motor and sensory deficits
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zone 2
distal to zone 1, containing deep branch only
motor deficits with intact sensation
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zone 3
distal to zone 1 and radial to zone 2, containing superficial branch only
hypothenar eminence, ulnar side 4th finger, and entire 5th finger sensory deficits
Etiology
Various causes include 2,4:
sports or occupation-related, e.g. cycling, bench press, push-ups
ulnar artery thrombosis
masses, e.g. ganglion cysts, lipomas, pseudoaneursm
thickened ligaments
penetrating trauma
variant muscles, e.g. accessory abductor digiti minimi
variant nerve routes
Radiographic features
Plain radiograph
Radiographs of the wrist can be helpful in identifying hook of hamate fractures.
Ultrasound
Ultrasound can be useful to assess for various causes as well as identify and ulnar nerve swelling. The ulnar nerve can be assessed as well as the superficial and deep branches, with the bifurcation occurring at the level of the hook of hamate and the branches divided by a fibrous arch 4. Comparison of the right and left ulnar cross-sectional areas may be useful as there is great individual variability 5.
MRI
MRI is only indicated in patients that have symptoms not consistent with ultrasound findings, symptoms persisting after surgery and a suspected mass lesion.
T1 weighted MRI is the preferred method of identifying structures in Guyon's canal. The findings in MRI are similar to that of ultrasound, however, MRI is more sensitive and accurate. Furthermore, the size and signal intensity of the ulnar nerve can be assessed on an MRI 3.
Treatment and prognosis
The treatment of Guyon's canal syndrome is dictated by its etiology.
Conservative management includes physiotherapy exercises, non steroidal anti-inflammatories (NSAIDs) and wrist braces.
Surgery may be indicated in some patients that have failed to respond to conservative management or if an acute cause like ulnar artery thrombosis has been identified.