Clinical scenarios Flashcards
- A 21-year-old student attends A&E after a firework they were holding exploded, splitting open the web between the thumb and index finger. The wound was cleaned and sutured and a K-wire was inserted to stabilise the first carpometacarpal joint. The K-wire was removed 6 weeks post-surgery. A subsequent neurological examination found: sensory loss on the volar (palmar) surface and nail bed of the thumb, and on the lateral side and nail bed of the index finger. Sensation on the medial side and proximal dorsal skin of the index finger and palm were normal. Sensation in the other digits was normal. There was weakness in abduction and opposition of the thumb. Adduction of the thumb was unaffected
Explain the anatomical basis of the student’s neurological signs.
The median nerve has been injured. The nerve roots are C6-T1.
Sensory loss on the palmar surface and the nail bed of the thumb and on the lateral side and the nail bed of the index finger suggests damage to the palmar digital branch of the median nerve. The palmar digital branch of the median nerve provides sensory innervation to the palmar surface and fingertips of the lateral 3.5 digits (including the nail beds).
Normal sensation on dorsal skin indicates that the radial nerve is not affected as the radial nerve innervates the dorsal surface of the lateral 3.5 digits and the dorsal skin. Normal sensation to the palm indicates that the palmar cutaneous branch of the median nerve is not affected. Normal sensation on the medial side indicates that the ulnar nerve is intact.
The opposition of the thumb is controlled by opponens pollicis and abduction of the thumb is controlled by abductor pollicis brevis which are innervated by the median nerve – so weakness in these areas suggests damage to the median nerve.
