What are the treatment options for a radial nerve injury causing middle finger drop in an adult with no significant past medical history after receiving an intramuscular (IM) injection in the deltoid muscle?

Radial Nerve Injury from Deltoid Intramuscular Injection

Initial Management: Conservative Approach with Close Monitoring

For a radial nerve injury causing middle finger drop after deltoid IM injection, initial management should be conservative with observation and physical therapy for 3-6 months, as most iatrogenic nerve injuries from injections recover spontaneously with supportive care. 1, 2

Immediate Assessment and Documentation

• Document the exact injection site relative to anatomical landmarks (distance from acromion, position on deltoid) to determine if the injection was given in an unsafe zone 2, 3
• Perform baseline electrodiagnostic studies (EMG/NCS) within 3-4 weeks of injury to establish the severity and pattern of nerve damage (axonal loss vs. neurapraxia) 1, 2
• Assess the complete radial nerve distribution, not just finger extension—evaluate wrist extension, thumb extension, and sensory function over the dorsal first web space 1

Critical pitfall: The radial nerve itself does not typically cause isolated middle finger drop. True radial nerve palsy causes wrist drop and loss of finger extension at the metacarpophalangeal joints. If only the middle finger is affected, consider alternative diagnoses including posterior interosseous nerve injury or extensor tendon injury 1

Conservative Management (First 3-6 Months)

• Initiate physical therapy immediately focusing on passive range of motion exercises to prevent joint contractures and maintain muscle length 1
• Provide a dynamic wrist extension splint to maintain functional hand position and prevent flexion contractures during the recovery period 1
• Serial clinical examinations every 4-6 weeks to document any signs of recovery (return of muscle strength using Medical Research Council grading scale) 1
• Repeat electrodiagnostic studies at 3 months if no clinical improvement is evident to assess for reinnervation potentials 1, 2

Surgical Intervention Criteria

If no recovery is evident by 3-6 months post-injury, surgical exploration with nerve transfer should be considered rather than waiting longer, as outcomes deteriorate significantly after 6 months 1

Nerve Transfer Surgery (Preferred Surgical Option)

• Median to radial nerve transfer is the recommended surgical approach for radial nerve palsy, involving coapting branches of flexor carpi radialis and flexor digitorum superficialis nerves to the posterior interosseous nerve and extensor carpi radialis brevis 1
• Timing is critical: Surgery performed within 6 months of injury yields significantly better outcomes (M4+ strength) compared to delayed surgery at 8 months (M2- strength) 1
• Expected outcomes: Independent wrist extension of M4+ in all patients and independent finger extension of M4+ in 70-90% of patients when surgery is performed within the optimal timeframe 1

Nerve transfer is superior to tendon transfer because it restores independent finger function and maintains grip strength through preserved wrist and finger extension, which is critical for fine motor tasks 1

Alternative: Tendon Transfer

• Tendon transfers are considered gold standard by some due to faster recovery and technical ease, but they do not restore independent finger function and result in functional deficits for fine hand movements 1
• Reserve tendon transfers for patients who present very late (>12 months), have failed nerve transfer, or require rapid return to basic function 1

Anatomical Context and Prevention

The injury likely occurred because the injection was given too high on the deltoid muscle (in the upper half), where the axillary nerve and its anterior branch are vulnerable 2, 3, 4

• Safe injection zone: 4 fingerbreadths (approximately 9 cm) below the mid-acromion point, or at the midpoint between the acromion and deltoid tuberosity with the arm abducted to 60° 5, 4
• The axillary nerve is located approximately 8.2 cm from the mid-acromial point, making upper deltoid injections particularly hazardous 5
• Injections should never be given in the upper half of the deltoid muscle to avoid neurovascular injury 5, 3, 4

Prognosis

• Most iatrogenic nerve injuries from IM injections recover spontaneously within 3-6 months with conservative management 2, 3
• Direct mechanical trauma is the most likely mechanism, though chemical neurotoxicity from the injected medication cannot be excluded 2
• Early surgical intervention (within 6 months) for non-recovering injuries provides excellent functional outcomes with M4+ strength in most patients 1