Vulnerability of the recurrent laryngeal nerve in the anterior approach to the lower cervical spine

Anterior Approach to the Subaxial Cervical Spine: Pearls and Pitfalls

Since its introduction by Smith and Robinson, the anterior approach to the subaxial cervical spine has become one of the standard procedures for numerous cervical spine pathologies, including, but not limited to degenerative disease, trauma, tumor, deformity, and instability. Along with its increasing popularity and improvements in anterior instrumentation techniques, a comprehensive knowledge of the surgical anatomy during the anterior exposure is critical for trainees and experienced spine surgeons alike to minimize the infrequent but potentially devastating risks associated with this approach. Understanding the anatomy and techniques to minimize damage to relevant structures can reduce the risks of developing notable postoperative complications and morbidity.

Comprehensive Comparison of Right and Left Recurrent Laryngeal Nerves in the Tracheoesophageal Groove

OBJECTIVE

A left-sided cervical approach to esophageal mobilization is considered safer given the perceived oblique path and more lateral orientation of the right recurrent laryngeal nerve (RLN) in the tracheoesophageal groove. Given the risk of recurrent laryngeal nerve, the current study investigated if there are differences in right and left RLN location in the tracheoesophageal groove.

METHODS

Right and left RLNs were carefully exposed in human cadavers. Comparison of location was determined at tracheal rings 2, 4, and 6 using 3 parameters: depth of the RLN from the anterior margin of the tracheal ring, lateral distance of the RLN from the posterior margin of the tracheal ring, and distance of the RLN to the anterior midline trachea following the curvature of the trachea. Statistical analysis was used to determine differences between the right and left sides.

RESULTS

Compared with the right RLN, the left RLN was slightly over 1 mm deeper at the second tracheal ring. Despite this trend, there was no significant difference in RLN location between individual sides or as an aggregate for any of the 3 parameters at tracheal rings 2, 4, or 6.

CONCLUSIONS

Careful characterization of RLN location precludes avoiding hoarseness, aphonia, and vocal cord paralysis. Counter to common surgical perception and educational beliefs, this study demonstrated that right and left RLN anatomical courses do not significantly differ along the trachea. Therefore, ensnarement on either side during a blind mobilization of the cervical esophagus is equally likely to occur.

Anatomic and radiologic relationships of neck structures to cervical spine: implications for anterior surgical approaches

The position of the pharyngolaryngeal framework is very important in choosing the best surgical approach for cervical spine disease. The aim of the present paper is to investigate the position of the hyoid bone and cricoid cartilage in relation to the cervical spine. Moreover, the surgical implications for anterior transcervical approaches to the upper spine and the prevertebral space are discussed. To minimise complication rates and increase surgical effectiveness, the location and extent of the cervical spine disease should be evaluated in the context of the patient’s specific anatomy. A retrospective analysis of 100 cervical spine MRIs was conducted. Patients with diseases that could alter anatomic relationships of cervical structures were excluded. The mid-sagittal view of the hyoid and the inferior margin of the cricoid cartilage were projected perpendicularly to the anterior surface of the cervical vertebrae. The distance between these two landmarks was measured on the same view. The distribution of hyoid projections ranged between C2-C3 and C4-C5 intervertebral space, while the cricoid cartilage ranged between C4-C5 and C7-T1 intervertebral spaces. The mean distance between these two landmarks was 49.1 ± 7.7 mm, with statistically significant differences between males and females. The position of the cricoid cartilage significantly influenced the length of the pharyngolaryngeal framework, while the position of hyoid did not. A wide range of variability in the position of the hyoid bone and the cricoid cartilage in relation to cervical levels exists. This implies that an a priori association of a cervical level to neck structures at risk might be inaccurate. The use of these easily identifiable landmarks on pre-operative imaging may help to guide the choice among different anterior surgical approaches to cervical spine and reduce the risk of surgical complications.

Causes of Vocal Fold Paralysis

BACKGROUND

Vocal fold paralysis (VFP) can result from a variety of diseases or surgeries and has various causes. This study determined concurrent etiologies in patients who were treated in a teaching hospital (tertiary medical center).

METHODS

A retrospective review of medical records of patients with VFP from September 2010 to December 2019 was performed to determine the etiology. Patients with laryngeal/hypopharyngeal malignancies, those with incomplete examination and follow-up data were excluded from the study. During the follow-ups, cases involving recovery were also excluded.

RESULTS

One hundred and ninety-four patients with a determined etiology were included: 113 males and 81 females. Unilateral VFP was present in 178 patients, and 16 presented with bilateral VFP. The causes of unilateral VFP were surgical for 61.3%, neoplastic for 17.5%, idiopathic for 10.3%, traumatic for 1.5%, central for 4.7%, cardiovascular for 2%, radiation-induced for 1.5%, and inflammatory for 1%. Thyroidectomy was the most common surgery for unilateral VFP and was the cause for 54 patients. Lung cancer was responsible for 15 cases and was the most common neoplastic etiology of unilateral VFP. For those who presented with bilateral VFP, surgery was the most common cause and accounted for 56.3% of the incidences. In terms of gender, surgery was the most common cause for both sexes, accounting for 62 of 113 male patients and 57 of 81 female patients. Four cases recovered during the follow-ups and these were excluded.

CONCLUSION

Surgery and in particular, thyroidectomy, was the most common cause of VFP for these series. Central nervous system disorders were the cause of VFP (4.5%). Central nervous system disorders, especially cerebrovascular accidents that induced VFP, could not be neglected. Radiation-induced cranial nerve paralysis in the head and neck cancer was possible causes. The percentage for the causes of unilateral VFP, surgery increased and the percentage for neoplasm decreased for Taiwan.

Right- Versus Left-sided Exposures of the Recurrent Laryngeal Nerve and Considerations of Cervical Spinal Surgical Corridor: A Fresh-Cadaveric Surgical Anatomy of RLN Pertinent to Spine

STUDY DESIGN

Cadaveric study on fresh unprocessed, nonpreserved, undyed specimens which have not previously been reported.

OBJECTIVE

We aimed to perform surgically relevant exposures of the anterior cervical spine with particular attention to observing the potential vulnerabilities of the RLN on right and left.

SUMMARY OF BACKGROUND DATA

Vulnerability of the RLN in the anterior cervical spine approach on the right versus left is the subject of ongoing debate. Although most cadaveric studies focus on course variations, structural relations of RLN, they have been done in preserved (fixed) cadavers without relevance to the needs of spinal exposure.

METHODS

Twelve fresh undyed cadavers had extensive layer by layer dissections by 2 surgeons (one with extensive experience as anatomy dissector). Both sides were explored for vulnerability during cervical spinal procedures. Each dissection was carried out in a phased approach and deliberately explored beyond what can be afforded in live surgery to allow the reader to conceptualize a better view of the structures.

RESULTS

In all specimens, we consistently demonstrated that the right surgical corridor involved manipulation of the nerve and its branches especially below C5 to achieve optimum midline access: in the right corridor, the RLN is on its oblique course to the tracheoesophageal groove. On the left, RLN is already in the tracheoesophageal groove and out of the surgical field involving minimal direct mobilization of the nerve.

CONCLUSION

RLN surgical anatomy photographed here is novel in using fresh unprocessed cadaveric specimens which has previously not been reported.Right surgical corridor, below C5, involves retraction/manipulation of RLN for achieving optimum spinal midline access, highlighting potential surgical vulnerability of right RLN.

LEVEL OF EVIDENCE

3.

Right Versus Left Approach to Anterior Cervical Discectomy and Fusion: An Anatomic Versus Historic Debate

The debate over the influence approach sidedness has on the risk of recurrent laryngeal nerve palsy (RLNP) following anterior cervical discectomy and fusion (ACDF) has its origins with the introduction of the procedure for radicular pain in the 1950s. The recurrent laryngeal nerves follow disparate courses in the lower neck secondary to differences in embryogenesis. Because of these differences, some authors believe a right-sided approach increases the risk of RLNP. However, modern surgical series have not shown a clear risk of RLNP with a right- versus left-sided approach. By looking at the historical context surrounding the introduction of ACDF, we propose the dogmatic view of an increased risk of RLNP with a right-sided approach likely arose from a combination of theoretical anatomic risk and the early surgical experience of a pioneer of the procedure.

Platysma sparing approach to anterior cervical spine surgery: A less exposure surgery technique

Introduction

Authors aim to demonstrate the surgical technique and outcomes of using a platysma sparing approach to anterior cervical spine surgery.

Methods

Medical records of 496 prospective patients, group 1 (259 patients) with an outpatient platysma muscle-sparing approach. Group 2 (237 patients) with inpatient standard muscle-splitting approach.

Results

Intergroup comparison showed statistical significant improvement in VAS neck and NDI scores p = 0.009 and p = 0.012 and surgical operative time and estimated blood loss, p = 0.003 and p = 0.006 respectively.

Conclusion

This anatomy sparing technique demonstrates a safe, effective and reproducible approach to cervical spine surgery which is a goal of less exposure surgery philosophy.

Improvement of Swallowing Function After Surgical Treatment of Diffuse Idiopathic Skeletal Hyperostosis: Our Experience

OBJECTIVE

To investigate the swallowing improvement in patients who underwent a transcervical prevascular retrovisceral approach for symptomatic cervical diffuse idiopathic skeletal hyperostosis (DISH), by means of the 10-item Eating Assessment Tool (EAT-10) questionnaire.

METHODS

Retrospective observational study of 21 patients treated with a transcervical anterior prevascular retrovisceral approach for symptomatic DISH with dysphagia as the primary symptom. All patients underwent videofluoroscopic study of swallowing before surgery and the EAT-10 questionnaire before and after the surgical procedure.

RESULTS

A statistically significant (P < 0.001) improvement in the postoperative EAT-10 score was reported. Sixteen out of 21 patients (76.2%) had their symptoms completely resolved, with an EAT-10 score less than 3. These results were not influenced by age and sex nor by presence of tracheostomy. The preoperative EAT-10 score was consistently related to postoperative outcome. Patients with mild and moderate dysphagia had better Δ in EAT-10 scores than patients with severe and very severe dysphagia (P = 0.02).

CONCLUSIONS

Surgical management seems to be effective in resolving swallowing disorders related to this disease in a consistent percentage of patients. This evidence is supported by the statistically significant improvement in EAT-10 scores after treatment. Moreover, it might be postulated that early intervention can guarantee a higher success rate because patients with severe and very severe dysphagia had significantly smaller improvement.

Option for transverse midline incision and other factors that determine patient's decision to have cervical spine surgery

BACKGROUND

Authors aim to determine patients' preference for surgical incision and factors affecting the decision for surgery to the anterior neck.

METHODS

A questionnaire was presented prior to evaluation and if preceded to surgery followup given.

RESULTS

243 patients completed questionnaire, with 60% female population and younger than 50 years. 151 patients preferred a transverse midline incision with a statistically significant increase in outcomes and cosmesis importance and a decrease in the importance of board certification.

CONCLUSION

Findings of questionnaire demonstrate that patients' prefer a transverse midline anterior neck incision, with surgical outcomes being the overall factor affecting decision making.

Anatomic Relationship Between Right Recurrent Laryngeal Nerve and Cervical Fascia and Its Application Significance in Anterior Cervical Spine Surgical Approach

STUDY DESIGN

An anatomic study of anterior cervical dissection of 42 embalmed cadavers.

OBJECTIVE

The aim was to study the anatomic relationship between recurrent laryngeal nerve (RLN) and cervical fascia combined with the requirements in anterior cervical spine surgery (ACSS).

SUMMARY OF BACKGROUND DATA

There has been no systematic research about how to avoid RLN injury in anterior cervical spine surgical approach from the aspect of the anatomic relationship between RLN and cervical fascia.

METHODS

Forty-two adult cadavers were dissected to observe the relationships between RLN and different cervical fascia layers.

RESULTS

RLN pierced out the alar fascia from the inner edge of the carotid sheath in all cases, and the piercing position in 22 cases (52.4%) was located at the lower segment of T1. The enter point into visceral fascia of RLN was located at C7-T1 in 25 cases (59.5%). The middle layer of deep cervical fascia exhibited the most stable anatomic relationship with RLN at the carotid sheath confluence site. Pulling visceral sheath leftwards would significantly increase the RLN tension.

CONCLUSION

Using the close and stable relationship between RLN and cervical fascia could help to avoid RLN injury in anterior cervical spine surgical approach.

LEVEL OF EVIDENCE

4.

Do the complications increased in the anterolateral right-side approach to treat the cervical degenerative disorders? A retrospective cohort study

The dysphagia and recurrent laryngeal nerve (RLN) palsy are the most common complications of the patients who underwent anterior cervical surgery in the current literature. These morbidities have led to the study of the impact of sidedness in anterior cervical spine surgery. However, many reports documented the left-side was more effective and safe than right-side based on the anatomy. So the right-side approach is more challenging. We retrospectively study 503 patients with cervical degenerative diseases who underwent cervical spinal surgery using anterolateral right-side approach in our spine center from September 1999 to December 2012 and evaluate the efficient and safety of the anterolateral right-side approach to treat the cervical degenerative diseases. The overall mortality rate in our present report was 3.38% (17 of 503 patients). The most common complication which observed in 2.80% of our cases was dysphagia. Postoperatively, there was only one patient with hematoma and died (0.19%) and symptomatic recurrent laryngeal nerve palsy occurred in 0.39% of the cases. The anterolateral right-side anterior approach didn't increase the incidence of the dysphagia and recurrent laryngeal nerve (RLN) palsy.

Indications for Direct Laryngoscopic Examination of Vocal Cord Function Prior to Anterior Cervical Surgery

Recurrent laryngeal nerve palsy (RLNP) is among the most common complications in both thyroid surgeries and anterior approaches to the cervical spine, having both a diverse etiology and presentation. Most bilateral paresis, with subsequent devastating impact on patients, are due to failure to recognize unilateral recurrent laryngeal nerve paralysis and, although rare, are entirely preventable with appropriate history and screening. Recurrent laryngeal nerve palsy has been shown to present asymptomatically in as high as 32% of cases, which yields limitations on exclusively screening with physical examination. Based on the available literature, diagnosis of unilateral RLNP is the critical factor in preventing the occurrence of bilateral RLNP as the surgeon may elect to operate on the injured side to prevent bilateral paresis. Analysis of incidence rates shows postoperative development of unilateral RLNP is 13.1 (95% confidence interval [CI]: 6.1-28.1) and 13.90 (95% CI: 6.6-29.3) times more likely in anterior spine and thyroid surgery, respectively, in comparison with intubation. Currently, there is no consensus on when to order a preoperative laryngoscopic examination prior to anterior cervical spine surgery. The importance of patient history should be emphasized, as it is the basis for indications of preoperative laryngoscopy. Efforts to minimize postoperative complications must be made, especially when considering the rising rate of cervical fusion. This study presents a systematic review of the literature defining key causes of RLNP, with a probability-based protocol to indicate direct laryngoscopy prior to anterior cervical surgery as a screening tool in the prevention of bilateral RLNP.

Complications of Anterior and Posterior Cervical Spine Surgery

Cervical spine surgery performed for the correct indications yields good results. However, surgeons need to be mindful of the many possible pitfalls. Complications may occur starting from the anaesthestic procedure and patient positioning to dura exposure and instrumentation. This review examines specific complications related to anterior and posterior cervical spine surgery, discusses their causes and considers methods to prevent or treat them. In general, avoiding complications is best achieved with meticulous preoperative analysis of the pathology, good patient selection for a specific procedure and careful execution of the surgery. Cervical spine surgery is usually effective in treating most pathologies and only a reasonable complication rate exists.

Anterior cervical discectomy in a patient with huge thyroid tissue (goiter)

Enlarged thyroid gland (goiter) may hinder to reach anterior part of the vertebrae or may impose more retraction than usual. The patient had left arm pain, and his left biceps muscle strength was 3/5 and triceps muscle strength was 4/5. Physical examination of his neck showed no abnormality. We performed anterior cervical discectomy, but we did not reach to the anterior part of the vertebrae due to enlarged thyroid gland even making moderately forceful medial retraction. It is therefore, we performed thyroidectomy previously, and later we performed anterior cervical discectomy at the level of cervical 5-6 and cervical 6-7. It will be wise to excise the goiter and later continue to cervical discectomy rather than using forceful retraction in cases with no preoperative detection as in our case to prevent damage of the recurrent laryngeal nerve and hoarseness due to pressure effect of the medial retraction during the anterior cervical approach.

Vocal cord palsy after anterior cervical spine surgery: a qualitative systematic review

BACKGROUND CONTEXT

Vocal cord palsy (VCP) is a known complication of anterior cervical spine surgery. However, the true incidence and interventions to minimize this complication are not well studied.

PURPOSE

To conduct a systematic review to identify the incidence, risk, and interventions for VCP after anterior cervical spine surgery.

STUDY DESIGN

This is a qualitative systematic literature review.

SAMPLE

Prospective and retrospective trials of patients undergoing anterior cervical spine surgery that reported on postoperative VCP or recurrent laryngeal nerve palsy.

OUTCOME MEASURES

Primary: incidence of VCP after anterior cervical spine surgery; secondary: risk factors and interventions for prevention of VCP after anterior cervical spine surgery.

METHODS

Electronic searches were conducted on Ovid Medline, EMBASE, Cochrane Central Register of Controlled Trials, and Cochrane Database of Systemic Reviews for clinical studies reporting VCP in anterior cervical spine surgery, limited to studies published between 1995 and June 2013 in English and French languages. After selection of studies independently by two review authors, data on incidence, risk, and interventions were extracted. Qualitative analysis was performed on three domains: quality of studies, strength of evidence, and impact of interventions.

RESULTS

Our search has identified 187 abstracts, and 34 studies met our inclusion criteria. The incidence of VCP ranges from 2.3% to 24.2%. Significant heterogeneity in study design and definition of VCP were used in the published studies. There is good evidence that reoperation increases the risk of VCP. One study of moderate strength suggests that operating from the right side may increase the risk of VCP. Among the interventions studied, endotracheal tube (ETT) cuff pressure monitoring with deflation during retraction has shown to reduce the incidence from 6% to 2%, but this result was not confirmed by randomized control trials. Limited evidence exists for other interventions of intraoperative electromyographic monitoring and methylprednisolone.

CONCLUSIONS

Vocal cord palsy is a significant morbidity after anterior cervical surgery with incidence up to 24.2% in the immediate postoperative period, with a higher risk in reoperation of the anterior cervical spine. Moderate evidence exists for ETT cuff pressure adjustment in preventing this complication.

Factors Predictive of Voice and Swallowing Outcomes after Anterior Approaches to the Cervical Spine

Objective

To quantify the incidence of postoperative voice, swallowing, and other problems, including time to resolution following anterior transcervical approaches to the cervical spine, and to assess surgical factors associated with outcomes.

Study Design

Historical cohort study.

Setting

Academic medical center.

Subjects and Methods

One hundred eighty-eight consecutive patients with cervical spine disease who underwent an anterior transcervical approach to the spine by a single head and neck surgeon over a 4-year time period. Rather than primary, single-level approaches, all patients in this study had multilevel, high-cervical (above C4), low-cervical (below C6), and/or revision approaches. Postoperative voice, swallowing, and other complaints were measured as well as time to resolution using Kaplan-Meier method. Surgical factors related to outcomes were analyzed using regression analysis.

Results

Follow-up was available for 129 patients, with average and median time of 35 months. Seventy-seven patients (60%) had a postoperative issue, including 35 patients (27%) with postoperative voice complaint, 62 patients (48%) with postoperative swallowing complaint, and 16 patients (12%) with other problems. Swallowing and voice complaints persisted beyond 1 year in 28% and 9% of patients, respectively. Approaching spinal levels above C4 and exposing more than 3 spinal levels were 2 factors significantly related to voice and swallowing problems.

Conclusion

There is a high incidence of subjective voice and swallowing complaints following transcervical anterior approaches to the spine, and such complaints can persist beyond 1 year in many patients. Exposure of more than 3 spinal levels or above level C4 are 2 factors significantly associated with outcome.

Dysphagia and associated respiratory considerations in cervical spinal cord injury

BACKGROUND

Dysphagia is a relatively common secondary complication that occurs after acute cervical spinal cord injury (SCI). The detrimental consequences of dysphagia in SCI include transient hypoxemia, chemical pneumonitis, atelectasis, bronchospasm, and pneumonia. The expedient diagnosis of dysphagia is imperative to reduce the risk of the development of life-threatening complications.

OBJECTIVE

The objective of this study was to identify risk factors for dysphagia after SCI and associated respiratory considerations in acute cervical SCI.

METHODS

Bedside swallow evaluation (BSE) was conducted in 68 individuals with acute cervical SCI who were admitted to an SCI specialty unit. Videofluroscopy swallow study was conducted within 72 hours of BSE when possible.

RESULTS

This prospective study found dysphagia in 30.9% (21 out of 68) of individuals with acute cervical SCI. Tracheostomy (P = .028), ventilator use (P = .012), and nasogastric tube (P = .049) were found to be significant associated factors for dysphagia. Furthermore, individuals with dysphagia had statistically higher occurrences of pneumonia when compared with persons without dysphagia (P < .001). There was also a trend for individuals with dysphagia to have longer length of stay (P = .087).

CONCLUSION

The role of respiratory care practitioners in the care of individuals with SCI who have dysphagia needs to be recognized. Aggressive respiratory care enables individuals with potential dysphagia to be evaluated by a speech pathologist in a timely manner. Early evaluation and intervention for dysphagia could decrease morbidity and improve overall clinical outcomes.

Long-term follow-up results of the Cloward procedure for cervical spondylotic myelopathy

PURPOSE

To assess the long-term results of anterior cervical discectomy and fusion using the Cloward procedure for the treatment of cervical spondylotic myelopathy, and to identify possible clinical outcome predictors.

METHODS

A total of 14 cases with a 10-year postoperative follow-up were available (82.4 % of the surviving patients). Patients underwent preoperative and postoperative neurological examination. The symptom severity was graded according to the Nurick scale. MRI measurements were obtained preoperatively. Cervical spine radiographs were obtained preoperatively and at the time of follow-up.

RESULTS

The mean improvement of the clinical status of patients on the Nurick scale was 1.43 ± 0.51 (range 1-2) with respect to the baseline values (p < 0.001), with a 62.5 % recovery rate. A positive association between the improvement of the Nurick scale and the length of follow-up was detected with an age-adjusted univariate analysis (p = 0.042). The Nurick grade improvement was also directly related to preoperative lower limb hyperreflexia (p = 0.039), spasticity (p = 0.017), and bladder dysfunction (p = 0.048). At the time of follow-up, an adjacent discopathy was noted above and below the operated level(s) in eight and six patients, respectively.

CONCLUSIONS

The Cloward technique is a safe and effective procedure for the treatment of cervical spondylotic myelopathy. The patients' preoperative neurological status and the length of follow-up affect the grade of postoperative ambulatory improvement.

Clinically relevant anatomy of recurrent laryngeal nerve

STUDY DESIGN

An anatomic study of anterior cervical dissection of 11 embalmed cadavers.

OBJECTIVE

To determine the anatomic relationship of the recurrent laryngeal nerve (RLN) to the cervical spine and demonstrate vulnerability of the nerve during anterior surgical approach.

SUMMARY OF BACKGROUND DATA

The most common complications of anterior neck surgery are dysphagia and RLN palsy. The morbidity of these complications has led to the investigation of the impact of sidedness in anterior cervical spine surgery.

METHODS

Eleven adult cadavers (5 male/6 female) were dissected bilaterally to expose the path of the recurrent laryngeal nerve.

RESULTS

The right RLN branched from the vagus nerve at the level of T1-T2 or inferior in all specimens. After looping around the subclavian artery, the right RLN became invested in the tracheoesophageal fascia greater than 0.5 cm inferior to C7-T1 in all specimens. The RLN traveled superiorly, slightly anterior to the tracheoesophageal groove, before coursing between the trachea and the thyroid. In 82% (9 of 11) of right-sided dissections, the RLN entered the larynx at or inferior to C6-C7. After looping around the aortic arch, the left RLN was invested in the tracheoesophageal fascia inferior to the T2 level in 100% (10 of 10) of cadavers. The nerve traveled slightly anterior to the tracheoesophageal groove and within the tracheoesophageal fascia before coursing between the trachea and thyroid. In all the left-sided dissections, the RLN entered the larynx at or inferior to C6-C7.

CONCLUSION

This study found that superior to C7-T1, both RLNs had similar anatomic courses and received similar protection via surrounding soft-tissue structures. From an anatomic perspective, the authors did not appreciate a side-to-side difference superior to this level that could place either nerve under greater risk for injury.

Anterior approach for complex cervical spondylotic myelopathy

Cervical spondylotic myelopathy (CSM) is a slowly progressive disease resulting from age-related degenerative changes in the spine that can lead to spinal cord dysfunction and significant functional disability. The degenerative changes and abnormal motion lead to vertebral body subluxation, osteophyte formation, ligamentum flavum hypertrophy, and spinal canal narrowing. Repetitive movement during normal cervical motion may result in microtrauma to the spinal cord. Disease extent and location dictate the choice of surgical approach. Anterior spinal decompression and instrumented fusion is successful in preventing CSM progression and has been shown to result in functional improvement in most patients.

Papel da videoendoscopia da laringe no diagnóstico de lesão do nervo laríngeo recorrente na abordagem cervical anterior

INTRODUÇÃO: o reconhecimento da lesão do nervo laríngeo recorrente (NLR) após tratamento cirúrgico de hérnia discal cervical via anterior é importante na evolução clínica do paciente e, em especial, nos casos de reintervenção. O real papel da videoendoscopia da laringe (VEL) de rotina no pós-operatório não tem sido completamente estudado. OBJETIVO: identificar a prevalência de lesões do NLR em pacientes sintomáticos ou não através da VEL após cirurgia de hérnia cervical via anterior. MÉTODOS: no período de Junho de 2009 a Julho de 2010 selecionamos 30 pacientes submetidos a tratamento cirúrgico de hérnia discal no Hospital São Lucas da PUC-RS. Realizou-se avaliação por VEL no pré-operatório e no décimo dia após a cirurgia. Pacientes que apresentaram um resultado anormal da VEL foram considerados com lesão do NLR e foram reavaliados mensalmente até a recuperação espontânea, ou no período máximo de seis meses, quando a lesão foi considerada definitiva. RESULTADOS: encontramos evidência de lesão do NLR em 3/30 (10%) dos pacientes, sendo que todos se apresentavam assintomáticos no momento do exame. Dentre as lesões, 2/30 (66,6%) ocorreram após abordagem cirúrgica pelo lado direito e 1/30 (33,3%) pelo lado esquerdo. Não encontramos nenhuma lesão definitiva, sendo o período máximo de recuperação de 120 dias. CONCLUSÃO: a avaliação por VEL no período pós-operatório pode ser útil para diagnosticar lesões do NLR, principalmente em pacientes assintomáticos. A falta de suspeita clínica não exclui a possibilidade de lesão do LNR.

Anterior approaches to the cervicothoracic junction: a study on the surgical accessibility of three different corridors based on the CT images

To determine the location of left brachiocephalic vein (BCV) and tracheal bifurcation (TB) relative to the vertebral levels, and to ascertain the accessibility of three different corridors (C1: between the esophagus and trachea medially and the carotid sheath laterally, C2: between the right BCV and the brachiocephalic artery, and C3: between the ascending aorta and superior vena cava) for preoperative planning. From August 2008 to April 2009, normal chest CT scans of 150 subjects ranging in age from 18 to 78 years were selected. According to our definition, of the 150 studies, 132 T2 vertebral bodies (VBs) could be accessed through C1 (88.0%), 100 T3 VBs could be reached through C2 (66.7%), and 110 T4 VBs could be exposed through C3 (73.3%). The results suggest that the surgical accessibility of three different corridors is different and we conclude that T2, T3, and T4 are, respectively, readily accessible through C1, C2, and C3.

Comparison of retraction pressure between novel and conventional retractor systems—a cadaver study

Object

Sore throat, dysphagia, and dysphonia are very common after anterior cervical surgery; clinical studies show an incidence of up to 60% or more. Neural, mucosal, or muscular injuries during dissection or retraction are regularly discussed, but investigations are few. Retraction pressure causing ischemia might explain these complications. A new anterior cervical retractor system (Seex retractor) using novel principles has been introduced to surgical practice. There are isolated reported investigations comparing different anterior cervical retractors. Therefore, the purpose of this study was to measure retraction pressure on the aerodigestive tract in cadavers during the anterior surgical approach for cervical spine operations performed using either the conventional (Cloward) retractor system or the Seex retractor system. The goal was to find the significance of the shape of the retraction blades (flat vs curved) in retraction pressures.

Methods

In cadavers, the anterior cervical spine was approached surgically at the C3/4, C4/5, C5/6, and C6/7 levels. A simulated anterior discectomy procedure was performed using a Cloward retractor with curved blade, a Seex retractor with curved blade, and a Seex retractor with flat blade at each level. For each retractor application, an online pressure transducer (Tekscan pressure measurement system) is applied between the rear side of the medial retractor blade and medial soft-tissue complex. Retraction pressures are recorded twice for both retractors at each level. Average retraction pressure (ARP), average peak retraction pressure (APRP), pressure distribution along the area of retraction, pressure difference at the edge and surface of the retractor blades, pressure variation with flat and curved blades, and so on were determined and compared. One-way ANOVA and Tukey honestly significant difference tests were used for statistical evaluation.

Results

Forty sets of pressure recordings were made in 5 cadavers. The Cloward retractor system showed higher average contact pressure than the Seex retractor system in 36 sets. In 32 sets, the Cloward retractor system showed higher peak retraction pressure than the Seex retractor system. None of the recordings showed uniform pressure distribution over the retracted area. With the Seex retractor itself, the flat blade generated more peak retraction pressure than the curved blades in 28 sets of measurements; it was the reverse in 3 sets; and in 9 sets the peak pressure was almost the same. Higher retraction pressure was noted along the edges of retractor blades in general, and along the convexity of a curved blade. Those parallel bands corresponded to the edges of the retractor blades. The Seex retractor with a curved blade generated the lowest average retraction pressure and average peak retraction pressure (p < 0.01, ANOVA).

Conclusions

Retraction pressure was found not to be uniform all over the retracted surface. Higher retraction pressure was noted along the edges of retractor blades in general, and along the convexity of a curved blade. The conventional retractor system with a curved blade generated significantly higher retraction pressures than the novel Seex retractor with a curved blade.

Preoperative functional assessment of the recurrent laryngeal nerve in patients with cervical vertebra fracture: case report

OBJECTIVE

Injury to the recurrent laryngeal nerve may occur during surgical intervention to the anterior part of the neck. However, some disorders can lead to damage to the recurrent laryngeal nerve before surgery. We report 2 cases of lower cervical vertebra fracture, leading to 1-sided injury of the recurrent laryngeal nerve.

CLINICAL PRESENTATION

One man and 1 woman with neck injuries were admitted to our hospital. The man had a C7-T1 dislocation fracture, and the woman had a C6-C7 dislocation fracture. Both patients had similar fractures and similar clinical presentations. The distinctive feature of these cases is that both patients had dysphonia after the initial injuries but before surgery.

INTERVENTION

Both patients were treated surgically, and anterior and posterior cervical stabilization was performed. During surgical intervention to the anterior part of the neck for cervical fixation, the injured side (where the vocal cords did not move during an indirect laryngoscopy) was preferred.

CONCLUSION

Patients with a cervical vertebra fracture with dysphonia and hoarseness should be examined for vocal cord dysfunction. Surgical intervention should be performed on the side of the injured recurrent laryngeal nerve.

Preoperative Laryngeal Nerve Screening for Revision Anterior Cervical Spine Procedures

Objectives:

Anterior cervical spine procedures carry an inherent risk of recurrent laryngeal nerve (RLN) injury. Patients with persistent RLN paresis may be asymptomatic because of compensation from the opposite side. If such patients undergo an opposite-side anterior approach for revision surgery, they are at risk for a second RLN injury, creating the potential for bilateral vocal fold paresis and possible need for tracheotomy. A program of routine screening for laryngeal paresis was implemented for these patients. This retrospective study reviews the results of this screening process.

Methods:

Patients referred for preoperative laryngeal nerve screening were identified. Their charts were reviewed for the results of the videolaryngoscopic examination, and for any recommendations made based on the findings. Relevant history and other physical findings were recorded.

Results:

Fifty screening laryngeal examinations were performed in 47 patients, of whom 31 (66%) had previously undergone a single anterior cervical approach procedure, and 16 (34%) had undergone more than one. Thirteen of the examinations (26%) revealed abnormal laryngeal findings, including paresis or paralysis in 11 cases (22%), of which 5 were asymptomatic. The findings resulted in a recommendation of a cervical approach from the already-involved side. None of the revision procedures resulted in bilateral vocal fold paralysis. The risk of laryngeal nerve injury appears to increase as higher cervical levels are approached.

Conclusions:

Minimally symptomatic injuries of the laryngeal nerves from prior neck surgery create a potential serious risk of bilateral vocal fold paralysis with subsequent procedures. Preoperative laryngeal screening is a simple and effective method for reducing this risk.

Is dysphonia permanent or temporary after anterior cervical approach?

The rate, causes and prognosis of dysphonia after anterior cervical approach (ACA) were investigated in our clinical series. During a 10-year interval, 235 consecutive patients with cervical disc disease underwent surgical treatment using anterior approach. Retrospective chart reviews showed recurrent laryngeal nerve (RLN) injury in 3 (1.27%) patients. All three patients were men and only one patient had multilevel surgery. These patients had RLN injury after virgin surgery. Laryngoscopic examination demonstrated unilateral vocal cord paralysis in all patients who had postoperative dysphonia. No permanent dysphonia was observed in our series and patients recovered after a mean of 2 months (range 1-3 months) duration. Dysphonia after ACA was a rare complication in our clinical series. Pressure on RLN or retraction may result in temporary dysphonia.

Dysphonia and dysphagia after anterior cervical decompression

OBJECT

In this paper, the authors investigate the effects of anterior cervical decompression (ACD) on swallowing and vocal function.

METHODS

The study comprised 114 patients who underwent ACD. The early group (50 patients) was examined immediately pre- and postoperatively, and the late group (64 patients) was examined at only 3 to 9 months postoperatively. Fifty age- and sex-matched patients from the Department of Otorhinolaryngology-Head and Neck Surgery who had not been intubated in the previous 5 years were used as a control group. All patients in the early and control groups were examined by a laryngologist; patients in the late group were examined by a laryngologist and a neurosurgeon. Videolaryngostroboscopy was performed in all members of the patient and control groups, and the function of the ninth through 12th cranial nerves were clinically evaluated. Data were collected concerning swallowing, voice quality, surgery results, and health-related quality of life. Patients with persistent dysphonia were referred for phoniatric evaluation and laryngeal electromyography (EMG). Those with persistent dysphagia underwent transoral endoscopic evaluation of swallowing function and videofluorography.

RESULTS

Sixty percent of patients in the early group reported dysphonia and 69% reported dysphagia at the immediate postoperative visit. Unilateral vocal fold paresis occurred in 12%. The prevalence of both dysphonia and dysphagia decreased in both groups 3 to 9 months postoperatively. All six patients with vocal fold paresis in the early group recovered, and in the late group there were two cases of vocal fold paresis. The results of laryngeal EMG were abnormal in 14 of 16 patients with persistent dysphonia. Neither intraoperative factors nor age or sex had any effect on the occurrence of dysphonia, dysphagia, or vocal fold paresis. Most patients were satisfied with the surgical outcome.

CONCLUSIONS

Dysphonia, dysphagia, and vocal fold paresis are common but usually transient complications of ACD. Recurrent laryngeal nerve damage detected by EMG is not rare. Pre-and postoperative laryngeal examination of ACD patients should be considered.

Etiology of vocal cord paralysis

OBJECTIVE

Vocal cord paralysis (VCP) is a sign of a certain underlying disease, a diagnosis which can be attributed to various causes. This study intends to analyze the contemporary etiology of VCP in a tertiary medical center.

MATERIALS AND METHODS

A retrospective review of medical records from June 2000 to December 2004 of hospitalized patients with VCP was done to determine the etiology.

RESULTS

Two hundred and ninety-one patients with a determined etiology were identified, consisting of 176 males and 115 females. Unilateral VCP was present in 259 patients, while 32 presented with bilateral VCP. The causes were surgical in 40.2%, neoplastic in 29.9%, idiopathic in 10.7%, traumatic in 8%, central in 3.8%, radiation-induced in 3.4%, inflammatory in 2%, cardiovascular in 1.7% and other causes in 0.3% of the cases. Thyroidectomy represented the most common surgery for VCP and was the cause in 57 patients. Lung cancer was responsible for 34 cases and was the most common neoplastic etiology. In males, neoplasm was the most common cause occurring in 63 of 176 males, whereas surgery was most frequent in 59 of 115 females.

CONCLUSION

Surgical trauma, mainly thyroidectomy, is the most common cause of VCP in hospitalized patients. The possibility of a neoplasm must be ruled out before VCP is labeled idiopathic. A benign thyroid tumor could also cause VCP. Besides, radiation-induced cranial nerve paralysis in head and neck cancer may play a significant role.

Anterior cervical discectomy and corpectomy

OBJECTIVE

The objective of this review article is to describe the authors' operative technique for performing anterior cervical corpectomy and fusion.

METHODS

The authors reviewed their operative technique and experience to clearly detail the general methods utilized to safely and effectively perform anterior cervical corpectomy and fusion. Specific nuances peculiar to the authors' technique were identified and highlighted.

RESULTS

The operative technique for anterior cervical corpectomy, including nuances for enhancing ease or outcome of surgery, is described in detail. Drawings and photographs are included where appropriate to highlight specific aspects of the procedural technique.

CONCLUSION

Anterior cervical corpectomy and fusion is a well known technique that proceeds in a consistent and logical sequence of maneuvers. Specific technical nuances at various points enhance the ease and safety of the technique, as well as the completeness of the eventual result.

Effect of approach side during anterior cervical discectomy and fusion on the incidence of recurrent laryngeal nerve injury

OBJECT

This retrospective study was designed to determine whether side of approach during instrumented, one- or two-level primary anterior cervical discectomy and fusion (ACDF) affects the incidence of recurrent laryngeal nerve (RLN) injury diagnosed by observation of the vocal cords (OVC).

METHODS

Records of all patients who underwent one- or two-level instrumented primary ACDF (418 patients) between January 1995 and February 2004 were reviewed. Data collected from these charts included surgeon, patient demographics, preoperative diagnosis, side of exposure, number of vertebral levels fused, and presence of RLN injury diagnosed by OVC after referral for persistent dysphonia. Time from surgery to OVC for patients with right-sided exposures was not statistically different from that for patients with left-sided exposures. Of 418 patients, 278 (66.5%) had right-sided exposures and 140 (33.5%) had left-sided exposures. Eight RLN injuries (1.9%) were noted-five in patients with right-sided exposures (1.8%) and three in patients with left-sided exposures (2.1%). The difference between right- and left-sided injury rates was shown to be nonsignificant using Fisher exact tests.

CONCLUSIONS

Results indicate that, given the study's sample size, side of approach during instrumented, one- or two-level primary ACDF has no significant effect on RLN injury incidence in patients with persistent dysphonia referred for OVC. The definitive answer regarding the true incidence of RLN injury relative to approach side awaits a prospective study with preoperative, immediate postoperative, and periodic OVC in a large, homogeneous population with sufficient numbers of patients with right- and left-sided approaches.

Changing trends in the nature of vocal fold motion impairment

PURPOSE

Vocal fold motion impairment (VFMI) continues to be a dominant issue in laryngology. The objective of this study is to examine a contemporary population of patients with newly diagnosed VFMI and detect changes in the nature of the cases compared with previous reports.

MATERIALS AND METHODS

Eighty-four patients with newly diagnosed VFMI are identified from the first author's clinic over a recent 1-year period. Patient demographics, etiology, side, and nature of the impairment are determined from retrospective chart review.

RESULTS

Of the 84 patients, 47 (56%) are women and 37 (44%) are men. The average age of all patients is 53.4 years. Seventy-five (89.3%) of the 84 VFMIs were unilateral, with 11% (9/84) being bilateral. The left side was affected in 52% (39/75) of the patients; the right side was affected in 48% (36/75) of the unilateral cases. The motion impairment was complete in 61.3% (46/75) of the unilateral cases and partial in the remaining 38.7% (29/75). With regard to etiology, iatrogenic causes were the most prevalent with 47.6% (40/84) of the patients. Idiopathic cases comprised 36.9% (31/84) of the patients. Neoplasms (7.1%, 6/84) and miscellaneous causes (7.1%, 6/84) accounted for smaller portions of the remainder. Of the iatrogenic VFMI cases, 27.5% (11/40) followed cervical spine operations. Chest, intracranial, and thyroid surgery accounted for 6 (15%) patients each, as did endotracheal intubation (n = 6, 15%).

CONCLUSIONS

Compared with previous reports, the incidence of iatrogenic cases reviewed here is relatively high. Anterior cervical spine surgery surpassed thyroidectomy and all other procedures as the most common cause of iatrogenic VFMI in this contemporary study.

Anatomia microcirúrgica do nervo laríngeo recorrente: aplicações no acesso cirúrgico anterior à coluna cervical

OBJETIVO: Descrever a anatomia do nervo laríngeo recorrente (NLR) bilateralmente, correlacionando-a com os prováveis mecanismos de lesão na abordagem cervical anterior. MÉTODO: Foram examinados 12 cadáveres de adultos provenientes do Laboratório de Microcirurgia da Faculdade de Medicina da UFMG. Os dados foram analisados em termos de freqüência, média e desvio-padrão. RESULTADOS: O NLR esquerdo teve comprimento total médio de 9,4 ± 1,6 cm. Penetra na laringe em 36,3% dos casos na altura de C5, 18,2% de C4, 18,2% de C5-C6, 18,2% de C6 e 9,1% de C4-C5. Recorre em 45,4% dos casos na altura de T3, 18,2% de T3-T4, 18,2% de T4 e 18,2% de T5. O NLR direito teve comprimento total médio de 5 ± 0,3 cm. Penetra na laringe em 44,4% dos casos na altura de C5, em 44,4% de C6 e 11,1% de C3-C4. Recorre em 60% dos casos na altura de T1, 30% de C7 e 10% de T2. CONCLUSÃO: O NLR direito encontra-se mais vulnerável a lesões operatórias por dois aspectos diferentes e complementares: trajetória e comprimento. Devido ao fato de apresentar trajetória mais oblíqua e desprotegida, não se relacionando de forma íntima com o sulco traqueoesofágico, existe maior possibilidade de ocorrerem traumas diretos, como a compressão por retratores ou a secção acidental, principalmente nas abordagens envolvendo níveis vertebrais mais baixos. Da mesma forma, o seu menor comprimento favorece o estiramento de suas fibras durante a tração per-operatória.

Recurrent laryngeal nerve paralysis: anatomy and etiology

Etiologies of adult vocal paralysis are varied by the site of the lesion as well as the extent and cause of the damage. Most large series point to surgery and neoplastic causes for recurrent nerve paralysis. A detailed history is important when working up a patient with this voice disorder. Knowledge of the anatomy of the head, neck, and chest as well as the mechanisms behind vocal fold paralysis is essential in the evaluation and treatment of recurrent nerve paralysis. Many of the surgical and traumatic causes of hoarseness are from compression type injuries. Recovery is dependent on the type, extent, and site of nerve lesion. Familiarity with this data allows the otolaryngologist to tailor management to suit each patient with vocal fold paralysis.

Dysphagia, hoarseness, and unilateral true vocal fold motion impairment following anterior cervical diskectomy and fusion

The charts of 100 patients who underwent anterior cervical diskectomy with fusion performed at our institution between January 1996 and February 1999 were reviewed. The incidences of hoarseness, dysphagia, and unilateral true vocal fold motion impairment were calculated. Univariate logistic regression was used to estimate the relationship of several patient and technical factors to the rates of occurrence of hoarseness and dysphagia. Patient age was found to be a significant predictor of postoperative dysphagia (p < .006), with an odds ratio of 1.113 (95% confidence limits, 1.04, 1.21) per year of age. Other factors studied were not found to be significant predictors. The overall incidence of these complications from the world literature was also calculated. The overall incidences of dysphagia, hoarseness, and unilateral true vocal fold motion impairment in the literature were calculated as 12.3%, 4.9%, and 1.4%, respectively. We conclude that dysphagia, hoarseness, and unilateral vocal fold motion impairment continue to remain significant complications of anterior cervical diskectomy with fusion. Older patients may be at higher risk for dysphagia.

Titanium mesh cages for cervical spine stabilization after corpectomy: a clinical and radiological study

OBJECT

Reconstruction after anterior cervical decompression has involved the use of tricortical iliac crest bone or fibular strut grafts, but has been associated with significant morbidity. In this study the authors evaluated the efficacy of titanium mesh cages (TMCs) for stability and fusion following anterior cervical corpectomy.

METHODS

Thirty-seven patients were prospectively evaluated during a 4-year period. The majority presented with spinal cord compression (97%) often due to cervical spondylosis (87%). The TMC was filled with iliac crest bone chips or Surgibone and stabilized by anterior cervical plates (ACPs). The changes in settling ratio, coronal and sagittal angles, and sagittal displacement were determined at 3, 6, and 12 months; immediate postoperative radiographs were used as baseline. Flexion-extension radiographs and computerized tomography (CT) scans (obtained at 1 year) were examined to assess stability, fusion, and bone growth within the TMC. Complications such as settling, telescoping, migration, and pseudarthrosis were not observed. Dynamic radiography revealed spinal stability in all patients. Cage-related complications occurred in 2.7% (TMC malplacement [one patient]), surgery-related complications in 10.8%, and graft-related complications in 21.6%. Evidence of bone growth into the TMC was documented in 16 (95%) of 17 patients on CT scans. The mean cage height-related settling rates were 4.46% at 3 months (31 patients [p = 0.066]), 3.89% at 6 months (28 patients [p = 0.028]), and 4.35% at 1 year (27 patients [p = 0.958]). The mean sagittal displacement changed by 3.9% (23 patients [p = 0.73]). The mean coronal and sagittal angles changed 2.89 degrees (30 patients [p = 0.498]) and 2.09 degrees (29 patients [p = 0.001]) at 1 year, respectively, or at last follow up from baseline. No significant differences in the radiological indices were seen when multilevel vertebrectomy cases were compared with single-level vertebrectomy (p = 0.221), smoking status, or age. Conclusions. Titanium mesh cages, in combination with ACPs, are safe and effective for vertebral replacement in the cervical spine.

Swallowing and speech dysfunction in patients undergoing anterior cervical discectomy and fusion: a prospective, objective preoperative and postoperative assessment

Swallowing difficulties and dysphonia may occur in patients undergoing anterior cervical discectomy and fusion. The etiology and incidence of these abnormalities, however, are not well defined. In view of this, we performed a prospective, objective analysis of swallowing function and vocal cord approximation in patients undergoing anterior cervical discectomy and fusion. Twenty-three consecutive patients (22 male and one female, mean age 59 years) undergoing anterior cervical discectomy and fusion had standardized modified barium swallow study and videolaryngoendoscopy performed preoperatively and again at 1 week and 1 month postoperatively. Eleven patients (48%) had radiographic evidence of preoperative swallowing abnormalities. The majority of these patients had myelopathic rather than radicular findings (p = 0.03). None, however, had symptoms of swallowing dysfunction. Among these patients, one had worse function postoperatively, three had improvement, and function remained unchanged in seven. The preoperative swallowing assessment was normal in 12 patients (52%). Postoperative radiographic swallowing abnormalities were demonstrated in eight of these patients (67%). Preoperative vocal cord movement was normal in all patients. Postoperatively, vocal cord paresis was detected in two patients. The paresis was transient in one and permanent in the other. Age, previous medical history, operation duration, and spinal level decompressed were not significantly associated with the incidence of swallowing dysfunction. There was, however, a tendency for patients undergoing multilevel surgery to demonstrate an increased incidence of swallowing abnormalities on postoperative radiographic studies. In addition, soft tissue swelling was more frequent in patients whose swallowing function was worse postoperatively (p = 0.007). Postoperative voice and swallowing dysfunction are common complications of anterior cervical discectomy and fusion, although in the majority of patients these abnormalities are not symptomatic. Patients undergoing multilevel procedures are at an increased risk for these complications, in part because of soft tissue swelling in the neck.

Graft subsidence after instrument-assisted anterior cervical fusion

Object. Bone grafts used in anterior cervical fusion (ACF) may subside postoperatively. The authors reviewed a recent series in which instrument-assisted ACF was performed to determine the degree of subsidence with respect to fusion length, use of segmental screws, and patient smoking status, age, and sex.

Methods. Charts and implant records were reviewed for all 70 patients who underwent instrument-assisted ACF during a 2-year period. The procedures, grafting materials, plate types/lengths, and patient smoking status were recorded. The immediate postoperative and follow-up lateral radiographs were analyzed. The plate lengths and lengths of the fused segments were measured in a standardized fashion.

The mean intraoperative and follow-up fusion segment lengths were 54.3 and 51.9 mm, respectively. Greater subsidence occurred in multilevel fusions than in single-level fusions. There were noticeable changes in the position of plates or screws on 14 of 70 follow-up x-ray films. No new neurological deficits related to graft subsidence occurred, and the reoperation rate was 3%. There was no statistical relation between subsidence and the following variables: segmental fixation, smoking status, sex, age, or dowel size when corrected for length of the plate. Hardware migration correlated significantly with plate length in cases of two- and three-level fusions.

Conclusions. The length of a fusion segment decreases in the immediate weeks following instrument-assisted ACF. Construct length is the most important determinant of subsidence. When designing multilevel cervical constructs, consideration of the effects of graft subsidence may help to avoid hardware-related complications.

Microsurgical anatomy of the superior and recurrent laryngeal nerves

OBJECTIVE

To study the microsurgical anatomy of the superior laryngeal nerve (SLN) and recurrent laryngeal nerve (RLN) with respect to anatomic landmarks, and to identify their vascular supplies.

METHODS

The microsurgical anatomy of the anterior neck, the course of the right and left SLN and RLN and their variations were studied in 21 cadavers. Fresh cadavers were perfused with colored silicon dye to investigate the microvasculature in detail.

RESULTS

SLN originates from the inferior vagal ganglion at the C2 level and descends medially toward the thyrohyoid membrane. It branches into an external and an internal branch deep to the internal carotid artery at the C3 level. The external branch, along with the cricothyroid artery, descends deep to the superior thyroid artery toward the cricothyroid muscle. Accompanied by the superior laryngeal artery, the internal branch passes deep to the loop of the superior thyroid artery and pierces the thyrohyoid membrane. Both nerves reside in the fascia covering longus colli muscles and are supplied by their accompanying arteries. The loop of RLN is found at the T1-T3 level on the right, and more caudally at the T3-T6 level on the left, entering the larynx between C5-C7 levels on both sides. RLN receives arterial supply from the esophageal and tracheal branches of the inferior thyroid artery proximally, and by the inferior laryngeal artery distally.

CONCLUSION

Incidental intraoperative injury to the SLN and RLN potentially could be avoided by understanding the detailed course of each nerve with respect to the surrounding anatomic landmarks and by recognizing their blood supplies.

Recurrent laryngeal nerve injury with anterior cervical spine surgery risk with laterality of surgical approach

STUDY DESIGN

A detailed review of anterior cervical fusion procedures from a university-based spine specialty service was completed. Noted were the laterality of approach, number of levels, discectomy or corpectomy, use of instrumentation, and cases of reoperation.

OBJECTIVES

The primary purpose of the study is to determine whether there is in fact a greater risk of recurrent laryngeal nerve (RLN) injury with approach on the right or left side. Also evaluated is the risk with corpectomy, reoperative procedures, and instrumentation.

BACKGROUND

Anatomic considerations have been used as justification to determine the side of surgical approach. However, few clinical studies have delineated the side of surgical approach in their results.

METHODS

A total of 328 anterior cervical spine fusion procedures completed between 1989 and 1999 were reviewed. All speech changes reported were noted throughout follow-up.

RESULTS

There were 187 anterior discectomy and 141 corpectomy procedures. There were 21 reoperative anterior fusions. There were 173 procedures completed from the right side and 155 from the left. There were nine patients documented to have dysphonia after surgery. Five had a left-sided approach and four had a right-sided approach.

CONCLUSIONS

The incidence of RLN symptoms after surgery was 2.7% (9 of 328). The incidence of RLN symptoms was 2.1% with anterior cervical discectomy, 3.5% with corpectomy (5 of 141), 3% with instrumentation (8 of 237), and 9.5% with reoperative anterior surgery (2 of 21). There was a significant increase in the rate of injury with reoperative anterior fusion. There was no association between the side of approach and the incidence of RLN symptoms.

Anterior approach to the cervical spine: surgical anatomy

While performing the anterior approach to the cervical vertebral bodies, injury to important anatomic structures in the vicinity of the dissection represents a serious risk. The midportion of the recurrent laryngeal nerve and the external branch of the superior laryngeal nerve are encountered in the anterior approach to the lower cervical spine. The recurrent laryngeal nerve is vulnerable to injury on the right side, especially if ligation of inferior thyroid vessels is performed without paying sufficient attention to the course and position of the nerve, and the external branch of the superior laryngeal nerve is vulnerable to injury during ligature and division of the superior thyroid artery. Avoiding injury to the recurrent laryngeal nerve (especially on the right side) and superior laryngeal nerve is a major consideration in the anterior approach to the lower cervical spine. The sympathetic trunk is situated in close proximity to the medial border of the longus colli at the C6 level (the longus colli diverge laterally, whereas the sympathetic trunk converges medially). The damage leads to the development of Horner's syndrome with its associated ptosis, meiosis, and anhydrosis. Awareness of the regional anatomy of the sympathetic trunk may help in identifying and preserving this important structure while performing anterior cervical surgery or during exposure of the transverse foramen or uncovertebral joint at the lower cervical levels. Finally, the spinal accessory nerve (embedded in fibroadipose tissue in the posterior triangle of the neck) is prone to injury. Its damage will result in an obvious shoulder droop, loss of shoulder elevation, and pain. Prevention of inadvertant injury to the accessory nerve is critical in the neck dissection.