Classic history and presentation: The presentation is highly variable depending on the zone of compression and can include a combination of motor symptoms only, sensory symptoms only, or both. History usually includes either a compression lesion such as a ganglion within the ulnar tunnel, or recent trauma such as a hook of hamate fracture (typically in an overuse setting such as handlebar sports and cycling). Patients present with pain and paresthesias in the ulnar 1-1/2 digits and/or weakness in the intrinsics, small and ring finger flexion, and thumb adduction.
Prevalence: Less than 10 cases per 100 000 people per year.
- Age – Most commonly seen in the second to fifth decade of life.
- Sex / gender – More common in males.
Pathophysiology: Ulnar tunnel syndrome is most commonly caused by direct compressive pathology or surrounding trauma that can manifest as mixed motor / sensory symptoms. Compressive pathologies most commonly include ganglion cysts, while traumatic pathologies most commonly involve hook of hamate fracture, pisiform dislocation, or repetitive trauma such as in handlebar sports.
Grade / classification system: Classification is based on location of compression (zones of Guyon's canal).
- Zone 1 is proximal to bifurcation of nerve, caused by ganglia and hook of hamate fractures, and causes mixed motor sensory symptoms.
- Zone 2 surrounds the deep motor branch, caused by ganglia and hook of hamate fractures, and causes motor symptoms only.
- Zone 3 surrounds the superficial sensory branch, caused by ulnar artery thrombosis or aneurysm, and causes sensory symptoms only.