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Wrist drop after a night on the sofa
A 24-year-old man wakes after a night of heavy drinking. He fell asleep with his right arm hanging over the back of a chair, and now he can't lift his right wrist or straighten his fingers.
Step 1 of 4
Which nerve is most likely injured?
Correct answer: C
Wrist drop means the wrist and finger extensors are weak — all supplied by the radial nerve. Compression against the humerus with the arm over a chair back during deep sleep or intoxication is the classic "Saturday night palsy".
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C
Wrist drop means the wrist and finger extensors are weak — all supplied by the radial nerve. Compression against the humerus with the arm over a chair back during deep sleep or intoxication is the classic "Saturday night palsy".
Step 2 of 4
Elbow extension is strong and the triceps reflex is normal.
Where along the nerve is the lesion most likely?
Correct answer: B
The branches to triceps brachii arise proximal to the radial groove, so wrist drop with triceps spared puts the lesion at the groove. An axillary lesion also weakens triceps. A posterior interosseous lesion causes finger drop without wrist drop and no sensory loss; the superficial branch is purely sensory.
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B
The branches to triceps brachii arise proximal to the radial groove, so wrist drop with triceps spared puts the lesion at the groove. An axillary lesion also weakens triceps. A posterior interosseous lesion causes finger drop without wrist drop and no sensory loss; the superficial branch is purely sensory.
Step 3 of 4
Where would you test sensation to confirm radial nerve involvement?
Correct answer: D
The most reliable radial sensory test site is the dorsal first web space. The palmar index tip is median, the hypothenar eminence ulnar, the lateral forearm musculocutaneous, and the lower deltoid ("regimental badge") axillary.
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D
The most reliable radial sensory test site is the dorsal first web space. The palmar index tip is median, the hypothenar eminence ulnar, the lateral forearm musculocutaneous, and the lower deltoid ("regimental badge") axillary.
Step 4 of 4
Which pattern would point instead to a C7 radiculopathy?
Correct answer: C
C7: triceps weakness, a reduced triceps reflex and middle-finger symptoms (see cervical vertebrae). The other options describe posterior interosseous nerve syndrome, superficial radial neuropathy, an ulnar lesion and injury to the recurrent branch of the median nerve.
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C
C7: triceps weakness, a reduced triceps reflex and middle-finger symptoms (see cervical vertebrae). The other options describe posterior interosseous nerve syndrome, superficial radial neuropathy, an ulnar lesion and injury to the recurrent branch of the median nerve.
Key points
- Triceps weak → axilla; triceps spared with wrist drop → radial groove; finger drop without wrist drop → PIN.
- Radial sensory test site: the dorsal first web space.