Reinnervation of a transected nerve after thyroidectomy

1. Overview and principles

When the RLN is sacrificed during thyroidectomy, immediate reinnervation is the most physiologic means of preserving phonatory function. The primary aim is to re-establish motor input to the intrinsic laryngeal muscles to maintain muscle tone and prevent atrophy, even though true vocal fold movement rarely returns [3,4]. Reinnervation achieves dynamic neural tone rather than static medialization and can be performed with minimal added operative time in the thyroidectomy field. Fundamental principles include tension-free coaptation, meticulous handling of nerve ends, and alignment of fascicles under microsurgical magnification. The distal RLN stump should be identified and preserved whenever possible. Immediate intraoperative reconstruction produces better outcomes than delayed repair, as prolonged denervation leads to end-plate degeneration and fibrosis [3]. Papadopoulou et al. [8] reviewed 18 clinical studies and concluded that early repair consistently improves voice quality, regardless of technique. Representative clinical studies comparing reinnervation outcomes by technique are summaried in Table 1.

Table 1.

Representative clinical studies comparing reinnervation outcomes by technique

2. Direct end-to-end neurorrhaphy

Direct neurorrhaphy is preferred when both nerve ends are available and can be approximated without tension—typically when the transection is sharp and the segmental loss is less than 5 mm. Under microscopic visualization, the cut ends are freshened to healthy fascicles. The epineurium is coapted with two or three 9-0 nylon sutures using an interrupted pattern. A small amount of fibrin glue can supplement the repair to ensure fascicular contact and prevent suture-induced trauma. Gentle mobilization of the larynx and thyroid remnant can relieve minor tension at the coaptation site [3,4].

Miyauchi et al. [3] demonstrated that immediate direct repair during thyroidectomy leads to significant improvement in phonation, even in patients who already had preoperative paralysis. Postoperative electromyography (EMG) showed reappearance of motor unit potential within 6 months. When feasible, direct repair is considered the standard method for recent transection with preserved nerve ends.

3. Interposition (cable) nerve grafting

If a segment of the RLN must be resected with tumor and the gap exceeds 5–10 mm, direct repair may cause traction, and an interposition graft is required. Suitable donors include the great auricular nerve, ansa cervicalis branch, or sural nerve [9,10]. After measuring the defect with the neck in a neutral position, a graft of slightly greater length is harvested to prevent tension. The graft is reversed to minimize misdirected branching, then coapted to the proximal and distal RLN stumps using 9-0 or 10-0 nylon sutures under microscopy. Each junction may be reinforced with fibrin sealant. Biological wraps (fascia or absorbable sheath) can be applied to prevent scar tethering [11,12].

When the proximal RLN is partially damaged but still conductive on intraoperative neuromonitoring, neurorrhaphy between viable fascicles and the graft can yield functional reinnervation. Early reconstruction—ideally during the same operation—allows regenerating axons to reach the target muscle before irreversible atrophy develops [4]. Cable grafting restores muscle tone and bulk in the majority of patients. Studies comparing direct repair and interposition grafting report equivalent improvements in maximum phonation time, shimmer, and perceptual voice quality [8]. Synkinetic reinnervation prevents muscle wasting, resulting in a stronger, steadier voice. However, delayed grafting beyond 6–12 months has inferior outcomes due to muscle fibrosis [13].

4. Ansa cervicalis to recurrent laryngeal nerve reinnervation

When the proximal RLN cannot be preserved—such as when invaded to its origin or sacrificed during central compartment dissection—the ansa cervicalis provides an ideal motor donor. It is purely motor, of comparable diameter to the RLN, and easily accessible in the thyroidectomy field [14]. The physiologic advantage lies in the ansa’s tonic firing pattern, which provides continuous low-level stimulation of the reinnervated laryngeal muscles. This maintains adduction and prevents atrophy while avoiding paradoxical synkinesis [7].

The main ansa trunk or a dominant branch is identified and used for end-to-end anastomosis. Postoperative EMG typically demonstrates reinnervation potentials within 3–6 months [15].

The ansa–RLN technique has shown reproducible, long-term success. In a large series of 237 patients, Wang et al. [14] found that postoperative stroboscopy and acoustic measures were indistinguishable from those of normal controls. Similar results have been reported in other cohorts [15]. The donor site morbidity is negligible, and the procedure adds only 10–15 minutes to operative time. Because the reinnervated fold remains in a slightly adducted, tensioned position, the patient retains a strong, non-breathy voice while the contralateral fold handles abduction. This “physiologic medialization” makes the ansa–RLN method particularly suited for unilateral resection [15]. In practice, anatomical variations such as duplication of the ansa loop or dominance of the superior root should be recognized intraoperatively. When multiple donor branches are available, the branch with the largest diameter and closest proximity to the RLN stump is preferred to minimize tension and optimize axonal alignment [14,15].

5. Vagus-to-recurrent laryngeal nerve anastomosis

Vagus transfer is rarely indicated today but remains a salvage option when both the proximal RLN and ansa cervicalis are unavailable. Voice improvement is variable, and donor morbidity—including dysphagia, weak cough, and loss of vagal reflexes—limits its use [7,10].