Which muscle is the last to recover in posterior interosseous nerve (PIN) palsy following radial head fixation?

Recovery Pattern in Posterior Interosseous Nerve (PIN) Palsy Following Radial Head Fixation

The extensor digitorum communis (EDC) muscle to the middle and ring fingers is typically the last to recover in posterior interosseous nerve (PIN) palsy following radial head fixation via Kocher approach. 1

Anatomical Basis for Recovery Pattern

• The posterior interosseous nerve has a specific branching pattern at the distal edge of the supinator muscle that explains the recovery sequence 1
• In anatomical studies, the EDC muscles for the middle and ring fingers are primarily supplied by recurrent nerve branch(es) of the PIN, while the EDC muscles for the index and little fingers are supplied by separate nerve branches 1
• This distinct innervation pattern explains why middle and ring finger extension is often the last function to recover following PIN injury 1

Mechanism of PIN Injury in Radial Head Fixation

• PIN palsy can occur as a complication of the posterior (Thompson) approach to the proximal radius used during radial head fixation 1, 2
• The nerve injury typically occurs at the distal edge of the supinator muscle rather than at the proximal supinator (arcade of Frohse) 1
• Iatrogenic injury to specific EDC motor branches is the likely mechanism rather than injury to the main PIN trunk 1
• Post-operative hematoma and edema can also cause neuropraxia of the PIN, leading to temporary palsy 3

Clinical Presentation and Assessment

• Patients with PIN palsy present with inability to extend the fingers and thumb at the metacarpophalangeal joints while maintaining wrist extension 2
• Wrist extension is preserved but shows radial deviation due to intact extensor carpi radialis longus (ECRL) function 4
• Thorough motor examination should focus on individual finger extension patterns to identify specific muscle involvement 2
• Electromyography can help confirm the diagnosis and monitor recovery 1

Recovery Progression

• PIN palsy following radial head fixation typically shows gradual improvement over time 5
• Recovery follows a predictable pattern based on nerve regeneration and reinnervation of affected muscles 1
• The EDC muscles to the index and little fingers typically recover earlier due to their separate nerve branch innervation 1
• The EDC muscles to the middle and ring fingers are the last to recover due to their innervation by recurrent branches of the PIN 1

Management Considerations

• Most cases of PIN palsy following radial head fixation are neuropraxic injuries that recover spontaneously 3
• Conservative management with physical therapy and splinting is appropriate for most patients 2
• If no recovery is observed after 3-6 months, surgical exploration may be considered 5
• For persistent deficits, tendon transfer procedures can be performed to restore finger extension 4

Prevention of PIN Injury

• Careful surgical technique during radial head fixation is essential to avoid PIN injury 1
• Awareness of the PIN's anatomical course and its branches is crucial for surgeons 2
• Excessive retraction during the Kocher approach should be avoided 1
• Proper post-operative care, including avoiding excessive ice application, can prevent additional complications 2