Timing of Electrodiagnostic Testing After Humeral Shaft Fracture With Wrist Drop
A 34-year-old man is referred 5 days after a fall from a ladder caused a midshaft humeral fracture. He has a complete wrist drop, numbness over the dorsal first web space, and no triceps weakness. The fracture is being managed nonoperatively. The referring surgeon wants “an EMG to see if the nerve is severed” before deciding on exploration. Examination shows Medical Research Council grade 0 wrist extension, grade 4 triceps, and reduced brachioradialis strength.
1. Is 5 days the right time for this electrodiagnostic study? Justify your answer.
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Five days is generally too early to answer the surgeon’s question. After acute axonal injury, Wallerian degeneration takes roughly 2–3 weeks; before then, distal conduction and needle examination can look normal even with a severe lesion. An EMG at 5 days may confirm that the radial nerve is affected and help localize the lesion, but it cannot reliably distinguish neurapraxia from axonotmesis or determine whether the nerve is “severed.”
Unless there is a compelling reason-such as worsening deficit suggesting an expanding hematoma-I would wait until about 3–4 weeks for prognostic information.
2. If the study is performed now and shows normal radial sensory and distal motor responses, how do you interpret that?
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Normal radial sensory and distal motor responses at 5 days do not mean the nerve is intact; they may simply reflect incomplete Wallerian degeneration. Interpretation depends on the stimulation site: if the lesion is at the spiral groove, stimulating distal to the lesion can produce a normal response early. Needle examination may show reduced recruitment but no fibrillations yet. The study is therefore indeterminate for prognosis and should be repeated.
3. When should the study be repeated, and which findings predict recovery?
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Repeat at approximately 3–4 weeks. Findings that predict a good prognosis include preserved distal CMAP amplitude, absent or limited denervation, and early reinnervation (nascent motor units). Poor prognostic signs include absent distal CMAP, diffuse fibrillations, and no reinnervation by 3–4 months. If there is no clinical or electrical recovery by 3–4 months, surgical exploration may be considered.