What could be causing persistent wrist drop, weak wrist movement, and upper arm edema after an injection, with some improvement in finger drop and residual strength to carry weights?

Post-Injection Radial Neuropathy with Partial Recovery

This presentation is consistent with injection-induced radial nerve injury showing early signs of recovery, and the priority is to confirm the diagnosis with nerve conduction studies and ultrasound imaging while initiating conservative management with physical therapy. 1, 2

Diagnosis and Localization

The clinical pattern—persistent wrist drop with improving finger extension and preserved ability to carry weights—indicates a partial radial nerve injury at the upper arm level with ongoing reinnervation. 1, 2

Key Diagnostic Features

• Wrist drop (inability to extend the wrist) is the hallmark of radial neuropathy, occurring when the nerve is damaged proximal to the innervation of wrist extensors 1, 2
• Improvement in middle finger drop suggests recovering function of the posterior interosseous nerve branch, which controls finger extensors 2
• Preserved ability to carry weights (but not lift) indicates intact triceps function, localizing the injury distal to the triceps innervation in the upper arm 1, 2
• Upper arm edema at the injection site directly implicates iatrogenic nerve injury from either direct needle trauma, injection of medication into/around the nerve, or compression from hematoma formation 3

Immediate Imaging and Electrodiagnostic Workup

Obtain high-resolution ultrasound of the radial nerve from the spiral groove through the forearm to identify the exact site and nature of injury. 4, 2

• Ultrasound can directly visualize nerve discontinuity, focal thickening, altered echogenicity, and any compressive hematoma or fluid collection 2
• MRI with dedicated neurography sequences provides superior soft-tissue detail and should be obtained if ultrasound is equivocal or shows concerning features requiring surgical consideration 4, 2
• Nerve conduction studies and electromyography should be performed now (not delayed) to establish baseline severity and distinguish between demyelinating injury (better prognosis) versus axonal injury 1, 3

A common pitfall is delaying electrodiagnostic studies for 2-3 weeks—perform them immediately to document baseline function and guide prognosis. 1

Management Strategy

Conservative Treatment (First-Line for Most Cases)

Initiate aggressive physical therapy immediately focusing on wrist and finger extension exercises, with wrist splinting in neutral position to prevent contractures. 4, 1

• Wrist splints should maintain the wrist in 20-30 degrees of extension to prevent overstretching of denervated muscles and allow functional hand use 4
• Physical therapy should include passive range of motion exercises for all affected joints, progressive strengthening as motor function returns, and functional task training 4
• Most traumatic radial nerve injuries show spontaneous recovery within 3-6 months, with improvement typically beginning within 6-12 weeks 1, 3

Pain and Edema Management

Use topical NSAIDs as first-line treatment for localized pain and inflammation at the injection site. 5

• Elevation of the affected arm and compression garments may help reduce persistent edema 5
• Avoid systemic NSAIDs or corticosteroids unless specifically indicated, as steroids can impair nerve regeneration 6

Monitoring for Complications

Reassess clinically every 2-4 weeks to document progressive improvement in motor function. 5, 1

• Red flags requiring urgent surgical consultation include: progressive weakness despite conservative treatment, evidence of complete nerve transection on imaging, or no clinical improvement by 3 months 1, 2
• Repeat nerve conduction studies at 3 months if recovery plateaus to assess for ongoing reinnervation versus permanent axonal loss 1, 3

Prognosis and Surgical Considerations

The presence of partial recovery (improving finger extension) is a favorable prognostic sign indicating incomplete nerve injury with preserved axonal continuity. 1, 3

• Injection-related radial neuropathies typically have better prognosis than fracture-associated injuries, with most patients achieving functional recovery within 3-6 months 3
• Surgical exploration is indicated only if: imaging shows complete nerve transection, there is a compressive hematoma requiring evacuation, or no clinical improvement occurs by 3-6 months despite optimal conservative management 1, 2

Common Pitfalls to Avoid

• Do not assume this is a central lesion (stroke) simply because of wrist drop—the presence of localized edema at the injection site, unilateral involvement, and absence of other neurological signs confirms peripheral nerve injury 7, 8
• Do not delay physical therapy waiting for "spontaneous recovery"—early mobilization prevents contractures and optimizes functional outcomes 4
• Do not perform repeat injections in the same area or allow blood pressure cuff placement on the affected arm, as this can worsen nerve injury 3