Laryngeal Reinnervation: Non-Selective and Selective Procedures

1. Physiologic and Anatomic Basis

Nerve Characteristics

• The anterior motor branch of the RLN enters the larynx posterior to the cricothyroid joint
• First branches innervate the horizontal and oblique compartments of the posterior cricoarytenoid (PCA) before entering the interarytenoid (IA)
• The PCA nerve branch has slow-twitch characteristics (motor units of 200-250 muscle fibers)
• The IA muscle receives a branch from each RLN - giving it bilateral innervation
• Terminal branches innervate the LCA and TA muscles, which are fast-twitch fibers (motor unit sizes of 2-20 fibers)
• In some larynges, a SLN-RLN connection exists within the TA muscle

Muscle Characteristics Relevant to Reinnervation

2. Non-Selective Laryngeal Reinnervation

Definition and Rationale

• It maintains vocal fold muscle mass and tone
• It prevents progressive atrophy
• It restores adequate medial position for phonation

A. Anastomosis of the Divided RLN (End-to-End or Cable Graft)

• Performed when RLN is divided intraoperatively or identified acutely
• Immediate repair at the time of injury is feasible and practical
• Delayed repair (weeks to months) is also effective
• A systematic review (Fadhil et al., J Voice 2024, PMID 35667984) found that ansa cervicalis-to-RLN anastomosis (ARA) is effective at both immediate and delayed timepoints, with some evidence that early delayed repair may be superior to late delayed operations

B. Ansa Cervicalis-to-RLN Nerve Transfer (Most Common Non-Selective Technique)

1. Neck dissection with identification of the ansa cervicalis (typically the branch to the sternothyroid or omohyoid)
2. Division of the ansa branch
3. Identification of the distal RLN stump
4. End-to-end neurorrhaphy with fine sutures (9-0 or 10-0 nylon)
5. No tracheotomy required for unilateral paralysis

• Torrecillas et al. (Laryngoscope 2024, PMID 38279973): In 132 patients over 22 years, unilateral non-selective ansa-RLN reinnervation significantly improved maximum phonation time (MPT), voice handicap index (VHI), and patient-reported percent normal voice. Revision rate was 8.3% (comparable to framework surgery). Only factor predicting need for revision was longer time from nerve injury to reinnervation. Complication rate was 6.8%.

• Best results when performed within 6-12 months of nerve injury
• Innervation activity of the ansa is expected to change contraction characteristics of reinnervated laryngeal muscles toward the slower infrahyoid muscle phenotype

C. The Neuromuscular Pedicle (NMP) Technique (Tucker's Procedure)

NMP for Bilateral Vocal Fold Paralysis (Targeting PCA - Abductor Reinnervation)

1. Tracheotomy is performed first to secure the airway
2. Direct laryngoscopy to assess the larynx
3. A cervical incision is made; the ansa cervicalis branch to the omohyoid is identified
4. A segment of the omohyoid belly with its intact nerve supply is harvested as a pedicle
5. The thyroid ala is windowed - a segment of thyroid cartilage is removed while leaving the inner perichondrium intact
6. The inner perichondrium is incised to expose the PCA muscle
7. The NMP is sutured to the PCA with 2-3 sutures of 5-0 nylon (abrasion of the PCA surface is not required)

• Tucker reported ~40% had airway improvement with visible inspiratory vocal fold motion; ~20% had no improvement; the remainder had airway improvement only with increased respiratory demand
• A review of 214 patients showed 74% long-term success rate (defined as decannulation with improved airway not limiting daily activities)
• A second NMP to the contralateral PCA can be performed for inadequate first results

NMP for Unilateral Vocal Fold Paralysis (Targeting LCA - Adductor Reinnervation)

• No tracheotomy performed
• Recipient muscle is the LCA (not PCA)
• A block of thyroid cartilage is removed from the lower half of the thyroid ala (preserving the inferior cartilage margin)
• NMP sutured to the exposed LCA with 2-3 sutures of 5-0 nylon
• Modification: two pedicles from separate strap muscles may be placed into the recipient muscle

• Tucker (1989): 88% success rate (defined by voice improvement, fold adduction, and pitch change)
• May and Beery: 95% had variable voice improvement (19/20 patients)
• NMP + Type I thyroplasty: improved voice outcome with reduced long-term deterioration
• NMP + arytenoid adduction (AA): improved subjective results at 2 years vs. 6 months, and superior to AA + thyroplasty alone; supported by EMG evidence of TA activation during phonation

3. Selective Laryngeal Reinnervation

Definition and Rationale

• Bilateral vocal fold paralysis (must selectively target the PCA/abductor to restore airway)
• Spasmodic dysphonia (selective denervation-reinnervation of adductor branches)

A. Selective Abductor Reinnervation - Phrenic Nerve Transfer

• Its activity pattern (inspiration-synchronous) matches PCA activity (which also fires 40-100 ms before the diaphragm during inspiration)
• It provides the appropriate physiologic input to drive abductor motion

• The phrenic nerve is identified in the neck running on the anterior surface of the anterior scalene muscle
• A branch or portion is anastomosed to the nerve branch supplying the PCA
• The anastomosis targets the distal motor branches at the level of individual muscles, not the RLN trunk

B. Selective Adductor Reinnervation

• Ansa cervicalis nerve-muscle pedicle laryngeal reinnervation without RLN transection
• Achieves glottal gap closure in unilateral VFP
• 12 patients followed 6-24 months: significant reduction in roughness (R) and breathiness (B), improved MPT to 15.8 sec, SPLmax to 91.5 dB, VHI reduction, and significant glottal gap reduction at T1 (3-6 months) - maintained to T3 (24 months)
• Outcomes comparable to standard laryngeal reinnervation and thyroplasty
• Advantage: Does not require RLN transection, preserves any remaining spontaneous reinnervation capacity

C. Selective Laryngeal Adductor Denervation-Reinnervation (for Spasmodic Dysphonia)

1. Transection of the adductor branches of the RLNs (both sides) - selective denervation
2. Reinnervation of these transected adductor branches with branches of the ansa cervicalis
3. The ansa provides low-level tonic (non-spasmodic) input to the adductor muscles

4. Direct Nerve Implantation

• A free nerve graft (or donor nerve branch) is directly implanted into the substance of the denervated laryngeal muscle
• Relies on axonal sprouting to occupy the original motor endplate sites
• Because PCA motor endplates concentrate in the midportion, precise placement offers a meaningful advantage for PCA implants; TA endplates are diffuse, reducing this positional benefit

5. Summary Comparison Table

6. Recent Advances (2023-2026)

1. Timing of ARA (Fadhil et al., J Voice 2024, PMID 35667984 - Systematic Review): ARA is effective at both immediate and delayed timepoints. Early delayed repair may be better than late delayed repair. Immediate ARA offers practical advantages (one surgery). Comparative data between immediate vs. delayed is still insufficient for definitive recommendations.
2. Long-term outcomes of non-selective reinnervation (Torrecillas et al., Laryngoscope 2024, PMID 38279973): Non-selective ansa-RLN reinnervation provides reliable durable improvement. Revision rate of 8.3% is favorable. Earlier surgery predicts better outcomes - the only independent predictor of needing revision.
3. Complementary ANMP-LR without RLN transection (Mueller et al., Laryngoscope Investig Otolaryngol 2025, PMID 40007737): An important advance allowing ansa cervicalis NMP reinnervation without sacrificing the RLN, preserving any residual/spontaneous recovery potential. Patients with unfavorable laryngeal synkinesis may still need standard LR with RLN transection.
4. Pediatric laryngeal reinnervation trends (Schuman & Ongkasuwan, Int J Pediatr Otorhinolaryngol 2025, PMID 40561875): Growing adoption of reinnervation in pediatric bilateral VFP.
5. Pediatric bilateral VFP surgery (Nemry & Lechien, J Otolaryngol Head Neck Surg 2024, PMID 39423048 - Systematic Review): Comparative review of reinnervation vs. other surgical approaches in children.

Key Clinical Pearls

• Non-selective reinnervation = synkinesis + tone preservation = adequate for unilateral VFP voice restoration
• Selective reinnervation = the goal when coordinated movement is needed (bilateral VFP requiring abductor reinnervation, or spasmodic dysphonia)
• The ansa cervicalis is the workhorse donor nerve (most procedures); the phrenic nerve is the best donor for abductor (PCA) selective reinnervation
• Motor fiber mismatch (slow infrahyoid fibers reinnervating fast laryngeal muscles) is an inherent limitation of all ansa-based procedures but is clinically acceptable in non-selective reinnervation
• All reinnervation procedures benefit from early timing - within 6-12 months of injury before irreversible muscle atrophy
• Reinnervation can be combined with framework surgery (thyroplasty, arytenoid adduction) for enhanced and more durable results