Does the right-sided approach in anterior cervical spine surgery increase the risk of recurrent laryngeal nerve injury?: a narrative review

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Abstract

Introduction

Injury to the recurrent laryngeal nerve (RLN) is a potentially devastating complication of neck surgery. The RLN innervates the intrinsic muscles of the larynx (except the cricothyroid) and provides sensation to the larynx below the glottis. Injury to the RLN can impair voice, swallowing, and airway function, profoundly affecting a patient’s quality of life [1]. Temporary RLN dysfunction after anterior cervical spinal surgery is relatively common but often unrecognized, whereas permanent RLN dysfunction is uncommon. Nevertheless, RLN injury remains a serious complication for spinal surgeons to consider [2].

Anatomically, the right RLN is thought to be at greater risk of injury during anterior cervical spinal approaches [3]. The right RLN is more exposed in the surgical field as it follows a shorter, more oblique course after looping around the subclavian artery and approaches the tracheoesophageal groove from a more lateral direction [4,5]. In contrast, the left RLN loops around the aortic arch at the level of the ligamentum arteriosum [1] and takes a more medial path in the neck [2,6,7] (Fig. 1A). This anatomical configuration may place the right RLN under greater tension when midline neck structures are retracted contralaterally [8]. RLN injury typically results from neuropraxia cause by stretch or compression (e.g., due to retraction or endotracheal cuff pressure), rather than from transection of the nerve [9,10].

Fig. 1

(A) Anatomical pathway of the left and right recurrent laryngeal nerves. (B) Pathway of a right nonrecurrent laryngeal nerve. This figure was created by the authors.

The right RLN also exhibits greater anatomical variability, which can complicate intraoperative identification [7]. In rare cases, it follows a nonrecurrent course (Fig. 1B), which is associated with a higher risk of injury [6,11,12]. Nonrecurrent laryngeal nerves occur in <1% of the general population [12,13] and may be anticipated if preoperative imaging reveals a retroesophageal subclavian artery [11].

Avoiding injury to the right RLN is therefore a key consideration in anterior cervical spine surgery [6]. Some authors have suggested that a left-sided approach may reduce the incidence of nerve injury [5,7]. However, there is no consensus on whether the side of surgical approach is a true risk factor for RLN injury [4], and current evidence remains inconsistent regarding the clinical relevance of these anatomical differences [14].

This study hypothesized that a right-sided approach carries a greater risk of RLN injury during cervical spine surgery. Although initially planned as a systematic review, the analysis was adapted to a narrative review with limited statistical evaluation due to the heterogeneity among available studies, which varied widely in surgical indications, timing, and technique of RLN assessment, and duration of follow-up.

Materials and Methods

Results

A total of 484 articles were retrieved through the initial database search, with an additional 28 identified via secondary searches on Google Scholar. After removing duplicates and screening titles and abstracts according to the eligibility criteria, 85 full-text articles were assessed, and 29 met the inclusion criteria (Fig. 2). Publication dates for the included studies ranged between 1973–2023.

Fig. 2

Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) flowchart of literature search to identify association between recurrent laryngeal nerve (RLN) injury incidence and side of surgical approach in anterior cervical surgeries.

Of the 29 included studies, 21 were retrospective reviews of patient records, and eight were prospective studies that investigated postoperative outcomes. Anterior cervical discectomy and fusion (ACDF) was the most frequently reported procedure, although several studies also included other anterior cervical spinal operations.

Across all studies, a total of 13,540 anterior cervical spinal procedures were reported. Of these, 1,137 utilized a left-sided approach and 12,403 used a right-sided approach. A total of 271 cases of RLN injury were reported, corresponding to a total incidence of 2.00% (271/13,540). Of these 271 RLN injuries, 31 cases were reported after left-sided approaches (incidence 2.73% [31/1,137]), while 240 cases were reported after right-sided approaches (incidence 1.94% [240/12,403]). The slightly higher incidence of RLN injury with left-sided approaches was not statistically significant (OR, 1.42; 95% CI, 0.97–2.08; p=0.05).

The indications for assessing patients for RLN injury were not consistent across the studies. Laryngoscopy, the gold standard for evaluating RLN function [15], was inconsistently applied. In most retrospective studies, laryngoscopy was performed only in patients presenting with dysphonia or dysphagia (classified by the authors as reactive laryngoscopy). This was performed at variable times during postoperative follow-up, and typically after a period of conservative management.

In contrast, all eight prospective studies and one retrospective study [16] performed routine postoperative laryngoscopy to identify vocal fold dysfunction regardless of symptoms (classified as routine laryngoscopy). This group included only 1,274 of the 13,540 total patients. Notably, a higher proportion of patients undergoing a left-sided approach had routine laryngoscopy compared to patients who had a right-sided approach (34% vs. 7%), which may have contributed to the higher detection rate of RLN dysfunction/injury in left-sided cases.

In the reactive laryngoscopy group, left-sided approaches demonstrated a slightly higher incidence of RLN injury, though the difference was not statistically significant (OR, 1.34; 95% CI, 0.77–2.33; p=0.05). The relatively small number of left-sided procedures compared to right (755 vs. 11,511) likely limited the statistical power of this comparison.

In the routine laryngoscopy group, the overall incidence of RLN injury was significantly higher than in the reactive laryngoscopy group, suggesting that asymptomatic RLN injuries are common and likely underdiagnosed when assessment is symptom-based. Within this subgroup, right-sided approaches were associated with a significantly greater incidence of RLN injury (OR, 0.47; 95% CI, 0.28–0.81; p=0.05) (Table 1, highlighted in bold), supporting the study hypothesis. However, only three of the nine studies in this group included left-sided procedures, and overall sample sizes were limited [2,10,16–22] (Table 2).

Table 1

Incidence of RLN injuries by side of procedure, method of investigation, and total incidence postoperatively and persisting at 3-months post-operation

Table 2

Characteristics of studies that conducted routine postoperative laryngoscopy in all patients

Follow-up data were heterogenous across studies, with marked variability in the timing and method of postoperative assessments, which limits the interpretability of results. At 3-month follow-up, the overall incidence of RLN injury decreased considerably in all patients (from 2.00% to 0.70%). While a slightly higher incidence persisted among patients with right-sided approaches in the routine laryngoscopy group, the difference was no longer clinically significant (OR, 0.85; 95% CI, 0.37–1.92; p=0.05) (Table 1).

Discussion

To date, no published study has focused specifically on the surgical approach side as a risk factor for RLN injury in anterior cervical spinal surgery. Recent studies, such as those by Oh et al. [23] and Abu-Gameh et al. [24], investigated the incidence and risk factors for RLN injury but did not include the side of approach in their analyses. The present review synthesized evidence from 29 studies to test the hypothesis that RLN injury is more common with a right-sided approach to the cervical spine.

The key findings of this study are as follows: (1) The most reliable data originate from studies employing routine postoperative laryngoscopy, as this method detects asymptomatic RLN dysfunction/injury that is otherwise underdiagnosed with reactive laryngoscopy. (2) Studies performing routine postoperative laryngoscopy reported a significantly higher rate of RLN injury with right-sided approaches. (3) There is substantial heterogeneity in the literature, with a lack of standardized indications and methods for outcome assessment. The duration of follow-up is also highly variable. (4) A considerable proportion of RLN injuries are minimally symptomatic or asymptomatic. (5) Most RLN injuries (between two-thirds to three-quarters) resolve within 3 months, though the evidence supporting this is limited by inconsistent follow-up protocols. (6) The vast majority of anterior cervical surgeries are performed via a right-sided approach.

This review identified significant methodological variability in the diagnosis and reporting of RLN injury. Prospective studies, such as Gowd et al. [10], conducted both preoperative and postoperative laryngoscopy in all patients, whereas retrospective studies, such as Beutler et al. [25], performed laryngoscopy only in symptomatic cases. The timing of RLN evaluation also varied widely. Some RLN injuries were diagnosed immediately postoperatively, while others were only diagnosed if the patients were symptomatic several weeks or months later. In some studies, the follow-up was continued for several months to years; however, many studies did not include any laryngoscopic follow-up after the initial diagnosis of RLN injury. None of the studies employed a validated scoring system to identify and/or quantify the symptoms of RLN injury.

Pooled data indicate an overall incidence of 1%–2% for transient RLN dysfunction following anterior cervical surgery, decreasing to approximately 0.5% at long-term follow-up. However, these estimates are influenced by the heterogeneity in diagnostic approaches and follow-up methods, limiting comparability between studies. This limitation has been similarly noted in other reviews [24]. Consequently, the authors deemed the data unsuitable for a systematic review.

The subset of studies employing routine postoperative laryngoscopy helped mitigate these limitations by providing an objective assessment of RLN function in all patients, regardless of symptoms. Consequently, the present review derived its most robust conclusions from a subanalysis of these studies, which yielded the most accurate estimate of true RLN injury incidence: approximately 9% following right-sided approaches compared with 4.5% following left-sided approaches, a statistically significant difference (OR, 0.47; 95% CI, 0.28–0.81; p=0.05). This finding supports the hypothesis that the right RLN is more vulnerable to injury during anterior cervical spinal surgery.

At 3 months postoperatively, there was a significant decrease in the overall incidence of RLN injury symptoms in all groups with no difference between sides of approach; however, lack of information about the timing of follow-up makes the significance of this finding uncertain. This recovery likely reflects the predominance of neuropraxic or axonotmetic injuries rather than a neurotmetic lesions [9,10]. Voice recovery may occur even without full (or any) restoration of vocal fold motion due to reinnervation and synkinesis [26]. In cases of neurotmesis, functional recovery can result from a combination of reinnervation, synkinesis, and intralaryngeal neural anastomoses, between the ipsilateral superior and recurrent laryngeal nerves and between the intralaryngeal branches of bilateral RLNs [27]. Nevertheless, a symptomatic RLN injury, even if transient, can be profoundly distressing for patients. Dysphonia and dysphagia not only impair the quality of life but may also contribute to significant morbidity. Vocal fold paralysis, the most severe sequela of RLN injury, can lead to dysphonia, dysphagia, aspiration, dyspnea, and psychosocial problems [2,28].

Asymptomatic RLN injury also carries important clinical implications, as subsequent surgery on the contralateral side of the neck poses a risk of bilateral RLN injury. This risk likely contributes to the markedly higher rates of dysphagia and dysphonia observed following repeat ACDF procedures [29].

The data reviewed in this study indicate that most RLN injuries following cervical spinal surgery are minimally symptomatic or entirely asymptomatic. In the acute phase, the ratio of symptomatic injuries to total RLN injuries (1.42% vs. 7.61%) suggests that only one in approximately 5.4 injuries produce symptoms. This observation aligns with previous reports but also implies a greater overall burden than previously recognized. Jung et al. [2] found that asymptomatic RLN injury was twice as common as symptomatic injury after cervical surgery, while Abu-Gameh et al. [24] similarly noted a higher total incidence of RLN injury compared with the rate of reported dysphonia. Comparable results have been observed in the thyroid surgery literature [15]. Collectively, these findings highlight the importance of routine laryngoscopic evaluation to determine the true incidence of RLN injury following any surgical procedure in the neck.

While performing routine postoperative laryngoscopy for all patients undergoing anterior cervical spinal surgery is impractical outside a research context, the findings of this study suggest that preoperative laryngoscopy should be performed in two clinical scenarios. First, preoperative laryngoscopy for all patients with a history of prior surgery in the neck, chest or around the skull base, even in the absence of symptoms suggestive of RLN dysfunction, due to the potentially life-threatening risk of airway compromise from bilateral RLN injury [30]. Second, preoperative laryngoscopy should be performed in any patient presenting with any symptom suggestive of RLN dysfunction, such as dysphonia and/or dysphagia to identify pre-existing vocal fold impairment and guide surgical planning.

The majority of spinal surgeons prefer a right-sided approach, as reflected by the marked disparity in case number between left- and right-sided surgeries (1,137 vs. 12,403, respectively). This preference is likely because, for most right-handed surgeons, the decompression phase of the procedure is technically easier to perform from the patient’ right side. Netterville et al. [5] and Johnson et al. [14] both concluded that the absolute risk of RLN injury remains low even with a right-sided approach, and that surgical success depends more on the surgeon’s technical competence [5,14]. Therefore, the choice of surgical laterality should take into account several factors, including the surgeon’s training, handedness, the level(s) of proposed surgery, the side of neurological compression, and the patient’s history of previous surgery in the neck (or chest or skull base) [25].

Conclusions

This review found that a right-sided anterior approach is a significant risk factor for RLN injury in cervical spine surgery. Importantly, this represents a modifiable risk factor: a left-sided approach should be favored when feasible, taking into account factors such as surgeon handedness, training, prior neck procedures, and underlying pathology. Asymptomatic RLN injuries appear to occur more frequently than previously recognized. To reduce the risk of bilateral RLN injury and potential airway compromise, preoperative laryngoscopy is recommended for all patients with a history of prior surgery involving the neck, chest, or skull base, even in the absence of symptoms. In addition, preoperative laryngoscopy should be performed in all patients presenting with any symptom suggestive of RLN dysfunction (such as dysphonia and/or dysphagia).

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