Acute Radial Nerve Palsy (Wrist Drop)
This presentation is most consistent with acute radial nerve injury causing inability to maintain wrist and finger extension (wrist drop), and you should immediately obtain high-resolution ultrasound of the radial nerve from the spiral groove through the forearm to identify the exact site and nature of injury. 1
Clinical Localization
The sudden inability to maintain dorsal flexion (wrist extension) with preserved ventral flexion localizes this to radial nerve dysfunction affecting the posterior interosseous nerve branch, which innervates the wrist and finger extensors. 2, 3
Key distinguishing features:
- Wrist drop is pathognomonic for radial nerve injury 1
- The history of forearm heaviness preceding acute weakness suggests either compression injury or evolving neuropathy 2
- Sudden onset ("suddenly the hand drops") indicates acute nerve dysfunction rather than progressive disease 4
Immediate Diagnostic Workup
First-line imaging: High-resolution ultrasound of the radial nerve from spiral groove through forearm to identify exact injury site and nature 1
If ultrasound is equivocal: MRI with dedicated neurography sequences provides superior soft-tissue detail and can detect nerve edema, compression, or structural injury 1
The ACR guidelines emphasize that dedicated neurography sequences (e.g., diffusion-weighted imaging) improve visualization of injured nerves in traumatic nerve injury of the hand and wrist 5
Differential Diagnosis to Consider
Most Likely: Radial Nerve Compression
- Spiral groove compression ("Saturday night palsy") from prolonged pressure 1
- Posterior interosseous nerve syndrome from compression at the arcade of Frohse 3
- Post-injection radial neuropathy if there was recent injection 1
Less Likely but Important to Exclude:
- Cervical radiculopathy (C7) - would typically have additional findings like triceps weakness and altered triceps reflex 3
- Central cord syndrome - would affect hands bilaterally with lower extremity sparing 5
- Stroke - would have additional upper motor neuron signs and cortical findings 4
Immediate Management
Initiate aggressive physical therapy immediately focusing on wrist and finger extension exercises 1
Wrist splinting in neutral position to prevent contractures, maintaining the wrist in 20-30 degrees of extension to prevent overstretching of denervated muscles 1
Pain management: Topical NSAIDs as first-line treatment for localized pain and inflammation 1
Critical Pitfalls to Avoid
- Do not assume this is a stroke without proper localization - isolated wrist drop without upper motor neuron signs points to peripheral nerve injury 4, 3
- Do not delay imaging - early identification of compressive lesions may allow for timely surgical decompression if indicated 1
- Do not allow wrist to remain in flexed position - this leads to contractures and poor functional outcomes 1
- Do not confuse with central causes - the isolated nature of wrist/finger extensor weakness without sensory level, upper motor neuron signs, or bilateral involvement excludes spinal cord or brain pathology 5, 4
Prognosis Considerations
Most peripheral nerve injuries from compression show spontaneous recovery over weeks to months with conservative management 6
Electrodiagnostic studies (nerve conduction studies and EMG) should be obtained if symptoms worsen or fail to improve after 2-3 weeks to assess for progression from demyelinating to axonal injury 6, 3
Surgical exploration is reserved for cases with complete nerve transection, progressive weakness despite conservative management, or space-occupying lesions identified on imaging 1, 2