The adductor pollicis muscle is innervated by the ulnar nerve, giving this guy a difficult time holding a sheet of paper.
Guyon Canal Syndrome is due to an Ulnar Nerve lesions and is associated with bicycle handlebar use.
Also FINGER abduction and adduction is mediated by ulnar nerve. The patient is having trouble with FINGER abduction and adduction.
The Froment sign is testing ADDUCTOR POLICIS ACTIVITY, which is mediated by the ULNAR NERVE activity. It is NOT testing thumb opposition, which would be mediated by the median nerve.
See Froment sign
Bicycle handlebar injury traditionally damages ulnar nerve @ the hook of the hamate bone
Most of intrinsic muscles of the hand are innervated by ulnar nerve - chronic compression at the hook of hamate could lead to nerve ischemia