Abstract
Background: The prevalence of dysphagia after anterior cervical decompression and arthrodesis is estimated to be 50% within one month and 21% at twelve months. However, its exact etiology is not well understood. The objective of the present study was to explore the relationship between intraoperative intra-esophageal pressure due to surgical retraction, esophageal mucosal blood flow at the level of surgery, and postoperative dysphagia. Our hypothesis was that sustained elevated pressure on the esophagus during anterior cervical arthrodesis is associated with postoperative dysphagia.
Methods: Seventeen selected patients scheduled for anterior cervical arthrodesis were studied. Throughout the procedure, intraluminal pressure in the upper esophageal sphincter was measured (mm Hg) with a custom-made manometer probe and mucosal perfusion was measured at the level of surgery with a laser Doppler flowmeter. The type of retraction chosen by the surgeon was noted. Postoperatively, the patients were specifically evaluated for dysphagia on the first postoperative day and at six weeks, three months, and six months postoperatively with use of the M.D. Anderson Dysphagia Inventory.
Results: Four of the eleven patients who had dynamic retraction and five of the six patients who had static retraction during surgery had postoperative dysphagia. In the group of patients with dysphagia, the average M.D. Anderson Dysphagia Inventory score decreased from 93.8 ± 12.1 preoperatively to 67.7 ± 11.4 on the first postoperative day (p < 0.001). The patients with dysphagia had a significantly higher average intraluminal pressure (60.8 ± 54.3 compared with 54.4 ± 51.8 mm Hg; p < 0.0001) as well as significantly lower average mucosal perfusion (26.1 ± 18.1 compared with 40.8 ± 26.2 tissue perfusion units; p < 0.0001) in comparison with the asymptomatic patients.
Conclusions: Patients with dysphagia following anterior cervical arthrodesis were exposed to higher intraoperative esophageal pressure and decreased esophageal mucosal blood flow during surgical retraction as compared with patients without dysphagia. In this small series, dynamic retraction seemed to be associated with a lower prevalence of postoperative dysphagia.
Level of Evidence: Therapeutic Level II. See Instructions to Authors for a complete description of levels of evidence.
Anterior cervical decompression and arthrodesis is a standard surgical procedure for the treatment of cervical radiculopathy, myelopathy, trauma, and tumors of the cervical spine1, and dysphagia is a common complaint in the postoperative period2-7. The prevalence of postoperative dysphagia has been estimated to range from 2% to 60% in retrospective reviews2-5, whereas in a large prospective study it was reported to be 50% within the first month and 21% at twelve months postoperatively6,7. Yue et al., in a longer-term retrospective review of seventy-four patients, reported that 35% continued to be moderately symptomatic with dysphagia seven years after surgery8.
The etiology of dysphagia following anterior cervical arthrodesis is not well understood. Risk factors include multiple surgical levels, female gender, longer operative time, and the use of implants6,7,9,10. Vocal cord paralysis has been documented in 2% to 6% of patients after anterior cervical arthrodesis11-13 and also has been previously associated with dysphagia11,14,15. Nevertheless, the rate of recurrent laryngeal nerve injury has been reported to be variable, ranging from 0.07% to 11%6,12-14, and cannot account for all of the patients presenting with dysphagia. A probable cause of recurrent laryngeal nerve injury is impingement on the intralaryngeal segment between surgical retractors and the endotracheal tube cuff13. It is possible that increased pressures during surgical retraction also may damage the intrinsic innervations of the hypopharynx and the upper esophageal sphincter, which may lead to dysphagia. Recently, investigators have described decreased tissue perfusion of the esophagus during and after anterior cervical arthrodesis16,17. Increased tissue pressure from retractors is thought to cause local ischemia but has not been related to the clinical manifestation of dysphagia.
The purpose of the present study was to explore the relationship between surgical retraction (quantified by increased esophageal intraluminal pressure and decreased esophageal mucosal blood flow) and postoperative dysphagia. Our hypothesis was that sustained elevated pressure on the esophagus during anterior cervical arthrodesis is associated with postoperative dysphagia.
Patient Population
Following institutional review board approval and informed patient consent, eighteen patients were entered into the study. Eligible subjects included patients who were scheduled for single or multiple-level anterior cervical arthrodesis for the treatment of cervical radiculopathy, myelopathy, or a combination of both. Patients with a history of neck surgery, cervical spine or neck trauma, tumors, infections, gastroesophageal reflux disease, or neurologic disorders associated with dysphagia (stroke, Parkinson disease, Alzheimer disease, head trauma, cerebral palsy, amyotrophic lateral sclerosis, and facial nerve palsy) were excluded from the study. One of the eighteen patients was lost to follow-up, and we were only able to obtain the immediate postoperative information. For this reason, the follow-up data from six weeks to six months were obtained for a total of seventeen patients.
Clinical Outcomes
Demographic data were registered at baseline (preoperatively), and generic health-related quality of life and functional status were assessed with use of the Short Form-36 (SF-36)18 at baseline and at six weeks and six months postoperatively. The Physical Component Summary (PCS) and Mental Component Summary (MCS) scores were calculated19.
Dysphagia was assessed with the M.D. Anderson Dysphagia Inventory20 at baseline, on the first postoperative day, and at six weeks, three months, and six months postoperatively. The M.D. Anderson Dysphagia Inventory is a validated and reliable self-administered questionnaire designed specifically for evaluating the impact of dysphagia on the quality of life. It is expressed on a 100-point scale, with 0 representing extremely low function and 100 representing normal function. For the purpose of the current study, dysphagia was considered to be clinically relevant when the score was <85 points.
Intraoperative Data Collection
A custom-made manometer probe (Konigsberg Instruments, Pasadena, California) with three pressure transducers (5 cm apart) was placed in the esophagus at the level of the upper esophageal sphincter (Fig. 1). This probe provided continuous measurements of intraluminal pressure (in mm Hg). A pressure transducer and monitor (model No. 90303B; Spacelabs Medical, Issaquah, Washington) was used as an isolated signal amplifier, which was connected to a 14-bit analog-to-digital converter (model NI-USB 6009; National Instruments, Austin, Texas). This signal was transmitted to a laptop personal computer equipped with National Instruments VI Logger Measurement and Automation Explorer Software (v. 3.1.1.3004; National Instruments). The collected data were subsequently exported to Excel (Excel 2003; Microsoft Corporation, Redmond, Washington) for interpretation. Data were collected every second throughout the entire operation.
Esophageal mucosal blood flow was measured with a Transonic BLF21 Laser Doppler Flowmeter and a Type I probe (Transonic Systems, Ithaca, New York). Perfusion was measured in tissue perfusion units (1 tissue perfusion unit = 1 mL/min/100 g of tissue). The obtained signal was connected to the same analog-to-digital converter previously described for the manometer probe. Data were also recorded every second throughout the intervention.
Techniques and Procedures
Following the induction of general anesthesia and the placement of an endotracheal tube, the manometer probe and the laser Doppler probe were placed in the upper esophagus at the level of surgery. The anesthesiologist (A.P.B.) was instructed to avoid the use of alpha-stimulating agents and to keep the blood pressure within 10% of the preoperative value. Fluoroscopy was used to confirm positioning of the manometer and laser Doppler probes at the beginning of the procedure (Fig. 1). The laser Doppler probe was placed such that it faced the side of the surgical incision and was at the level of the middle manometer probe, which, in turn, was placed at the level of the disc that was being operatively treated. For two-level anterior cervical arthrodesis, the probe was placed at the level of the intervening vertebral body. The endotracheal cuff was inflated to a level to just prevent air leak at the beginning of the procedure and was not repositioned after retractor insertion.
The left-sided Smith-Robinson surgical approach21 was used for all patients, and all of the operations were performed by one of the two senior authors, who had eleven (S.M.-L.) and more than twenty-five years of experience (C.R.C.) with the use of this technique. Once the anterior cervical fascia was exposed, the longus colli muscles were mobilized and retractor blades were positioned underneath their medial border. The operations consisted of one-level (eight patients) or two-level (ten patients) anterior cervical discectomy and arthrodesis with anterior plating and placement of an interposition allograft. The most frequent levels were C5-C6 (thirteen levels) and C6-C7 (ten levels), followed by C4-C5 (four levels) and C3-C4 (one level).
One of the surgeons used a static retractor system (self-retaining Trimline retractors; Medtronic Sofamor Danek, Memphis, Tennessee), and the other surgeon used dynamic retractors (Cloward handheld retractors; Cloward Instruments, Honolulu, Hawaii). The retractor blades were positioned bilaterally under the longus colli muscles for deep retraction.
Statistical Analysis
The data were exported to Statistical Analysis System software (SAS Institute, Cary, North Carolina). Nonparametric analysis was performed with use of the Fisher exact test. Pressure and blood flow were plotted against operative time (Fig. 2), and regression analysis was carried out. The t test was used to compare groups according to the type of retractor used and the presence or absence of symptoms. The comparisons controlled for the confounding variables of age, gender, body mass index, comorbid conditions, the level of arthrodesis, and the number of arthrodesis levels. The level of significance was set at p < 0.05. All values are expressed as the mean and the standard deviation.
The average age of the seventeen patients was 47.8 ± 9.1 years at the time of the index procedure. During surgery, dynamic (handheld) retractors were used for eleven of these seventeen patients and static (self-retaining) retractors were used for six. Nine of the seventeen patients presented with dysphagia after surgery, including four of the eleven patients in the dynamic retraction group and five of the six patients in the static retraction group.
In the group of patients who presented with dysphagia following surgery, the average M.D. Anderson Dysphagia Inventory score decreased from 93.8 ± 12.1 preoperatively to 67.7 ± 11.4 on the first postoperative day (p < 0.001). In contrast, in the group of patients who did not complain of dysphagia, the average M.D. Anderson Dysphagia Inventory score was 94.7 ± 4.7 preoperatively compared with 92.3 ± 4.9 on the first postoperative day (p = 0.180) (Fig. 3). Of the nine patients who had development of dysphagia, seven had recovery of the preoperative M.D. Anderson Dysphagia Inventory score by three months and eight had recovery of the preoperative score by six months.
Age, gender, body mass index, and baseline SF-36 scores were comparable between the group of patients who presented with dysphagia following surgery and the group of patients who did not present with this symptom (Table I).
The average SF-36 PCS score for all patients improved significantly, from 35.8 ± 8.5 at baseline to 47.3 ± 9.4 at the time of the six-month follow-up (p < 0.01). The average SF-36 MCS score did not vary significantly during the follow-up period, but nevertheless was within the average range for age and gender-adjusted normative data (42.9 ± 13.6 at baseline, compared with 50.5 ± 11.4 at six months).
Intraluminal Pressure and Perfusion
Mucosal blood flow decreased as intraluminal pressure increased. Figure 2 shows the data for a patient in the static retraction group, with the curve corresponding to the intraluminal pressure in the "intermediate" position mirroring the curve for mucosal blood flow. This finding was typical for all patients. A review of the pressure/perfusion curves for all patients revealed that static retractors were, in general, associated with more homogenous pressure and blood-flow curves than dynamic retractors were.
Analysis of the pressure and perfusion data demonstrated that most blood flow values of <20 tissue perfusion units occurred in association with intraluminal pressures exceeding 50 mm Hg. Decreasing perfusion, however, did not exhibit a linear correlation with increasing pressure (r2 = 0.234). Nevertheless, the average perfusion observed at pressures exceeding 50 mm Hg was significantly lower than that observed at lower intraluminal pressures (26.73 ± 22.37 compared with 41.1 ± 23.4; p < 0.0001).
Intraluminal Pressure, Perfusion, and Dysphagia
The patients who presented with dysphagia following surgery had a significantly higher average intraluminal pressure in comparison with those who did not present with this symptom (60.8 ± 54.3 compared with 54.4 ± 51.8; p < 0.0001) (Table I). In addition, the average perfusion was significantly lower in the symptomatic group than in the asymptomatic group (26.1 ± 18.1 compared with 40.82 ± 26.2 tissue perfusion units; p < 0.0001). The total operative time, from incision to skin closure, was comparable for both symptomatic and asymptomatic patients. The effect of the number of arthrodesis levels was also evaluated. Of the patients who presented with dysphagia, six of nine underwent a two-level anterior cervical arthrodesis, in contrast with four of eight patients without dysphagia. With the small number of subjects in the study, this difference was not significant (p = 0.18).
Dysphagia and Retractor Type
Postoperative dysphagia developed in five of the six of the patients in the static retractor group, compared with four of the eleven patients in the dynamic retractor group (p = 0.08). Although the average preoperative M.D. Anderson Dysphagia Inventory scores were comparable for the two groups (97.9 ± 2.6 for the static retractor group, compared with 94.3 ± 11.3 for the dynamic retractor group; p = 0.334), the average postoperative M.D. Anderson Dysphagia Inventory score was significantly lower in the static retractor group (69.2 ± 19 compared with 86.7 ± 11.7; p = 0.04).
With the numbers available, no difference was identified between the static and dynamic retractor groups with regard to body mass index (average, 29.3 ± 7.4 compared with 24.4 ± 3.6; p = 0.229), baseline SF-36 PCS scores (average, 36.5 ± 9.8 compared with 34.3 ± 4.7; p = 0.541), or baseline SF-36 MCS scores (average, 44.3 ± 11.3 compared with 39.3 ± 13.9; p = 0.506). The dynamic retractor group was, however, significantly older (average, 51.9 ± 6.8 compared with 39.5 ± 7.3 years; p = 0.002).
With the numbers available, no difference was detected between the static and dynamic retractor groups with regard to the duration of surgery (average, 115.8 ± 45.8 compared with 121.5 ± 37.9 min; p = 0.810), peak intraluminal pressure (174.4 ± 67.1 compared with 207.2 ± 74.3 mm Hg; p = 0.405), average intraluminal pressure (59.18 ± 26.5 compared with 57.4 ± 38.1 mm Hg; p = 0.927), or average perfusion (30.1 ± 18.1 compared with 34.6 ± 13.7 tissue perfusion units; p = 0.635) (Table II). The static retractor group had a more prolonged average ischemia time, as defined by the length of time with <20 tissue perfusion units, in comparison with the dynamic retractor group (49.1 ± 42.6 compared with 30.1 ± 31.1 minutes); however, this difference was not significant (p = 0.405).
Although dysphagia is a frequent complication of anterior cervical surgery, the etiology remains unclear. Nine of the seventeen patients in our study group had development of this symptom, which resolved by three months in seven cases and by six months in eight cases. Although different scoring systems were used, the rate of occurrence of this problem proved to be comparable with the findings of previous studies, which suggested rates of 50.2% at one month and of 28% to 32.2% at three months6,22. Thus, the threshold M.D. Anderson Dysphagia Inventory score of 85 points is probably analogous to the mild-to-moderate range of the Bazaz dysphagia score6. We did not follow these patients for longer periods because our interest was in the immediate occurrence of this problem, and in all cases but one the M.D. Anderson Dysphagia Inventory score had returned to the baseline value by six months.
Swallowing consists of three distinct phases, the oral, pharyngeal, and esophageal phases23. Dysphagia can occur as a result of abnormality in one or all of these phases in a given patient. In relation to anterior cervical surgery, the level of surgical exposure can affect specific phases. Surgery performed at or cephalad to the level of the third cervical vertebra (C3) places the glossopharyngeal and hypoglossal nerves at risk. These nerves are important in the oral phase of swallowing to project the food bolus into the pharynx. Surgery involving the C3 and C4 levels places the superior laryngeal nerve and the recurrent laryngeal nerve at risk and can affect the pharyngeal phase of swallowing. The esophageal phase can be affected by prevertebral swelling, by prominent hardware, and probably also by esophageal ischemia due to increased pressure by surgical retractors22,24. These factors probably could affect the intrinsic innervation of the upper esophagus in a fashion similar to that proposed for the pathogenesis of vocal fold paralysis, which affected 3.2% of ninety-four patients in a prospective series of patients who underwent anterior cervical arthrodesis15. It has been suggested that the recurrent laryngeal nerve is affected in its intralaryngeal portion by increased pressure between the endotracheal tube cuff and the surgical retractors13. However, in a prospective randomized trial, decreasing endotracheal tube cuff pressure did not seem to modify the incidence of decreased vocal fold function25. Recent studies have demonstrated increased pressure on the walls of the esophagus (exceeding mucosal perfusion pressure)16 following opening of the surgical retractors as well as a 70% decrease in esophageal wall perfusion17. These findings, however, have not been associated with clinical manifestations of dysphagia.
The findings of the present study suggest that mucosal perfusion had an inverse relationship with intraluminal pressure. The average perfusion observed in association with intraluminal esophageal pressures exceeding 50 mm Hg was significantly decreased when compared with that observed at lower intraluminal pressures. This finding is supported by previous reports16,17 in which hypoperfusion was detected as soon as the static retractors were opened.
In studies by Heese et al.16,17, perfusion decreased underneath the open retractors from an average baseline value of 107 tissue perfusion units to an average of 30 tissue perfusion units. In addition, seven of their fifteen patients demonstrated a reactive hyperemia following the release of retraction. Epi-esophageal pressure was concomitantly read underneath the medial retractor blade as well as on the mucosal side. These pressures were found to increase from a baseline of 9.8 to 92.7 mm Hg, exceeding mucosal perfusion pressure as well as mean arterial pressure. The authors did not define the limits for clinically relevant hypoperfusion but concluded that local ischemia of the walls of the pharynx and esophagus may be a crucial step in the development of postoperative dysphagia.
In our patients, the ranges and deviations of the intraluminal pressures seemed to be high, and this finding most likely reflects the need for varying degrees of exposure during the difficult parts of the surgical procedure. We did not find any means of controlling this effect; nevertheless, the deviations seemed to be quite similar between the static and dynamic retractor groups.
In the present study, patients in whom dysphagia developed after the procedure had significantly higher average intraluminal pressure throughout the operation as well as significantly lower average mucosal perfusion in comparison with those in whom dysphagia did not develop. Although mucosal perfusion seems to be dependent on the variations in intraluminal pressure, it might play a role in the development of dysphagia.
Dysphagia may present as a consequence of direct damage to the muscular walls or the myenteric plexus, and this damage may occur as a consequence of ischemia or as a consequence of sustained pressure. Histologic and electromyographic studies should clarify the exact nature of this problem.
Clinical and experimental studies have supported a threshold of 20 tissue perfusion units to define esophageal wall ischemia. Ikeda et al.24 used laser Doppler flowmetry to predict the success of the cervical anastomoses of retrosternal esophageal bypass for the treatment of esophageal cancer or chemical burns. Reasons for failure included the development of cervical fistulas, and patients with this finding consistently had intraoperative perfusion values of <20 tissue perfusion units24. These values also correlate well with those of a rodent experimental model in which the gastric mucosal perfusion decreased to similar values following left gastric artery occlusion26. Nevertheless, it is likely that less extreme hypoperfusion is required to induce neuromuscular alterations to the esophageal walls.
Because the present study was not designed to correlate dysphagia with the type of retraction used, the results should be viewed with caution. While patients in the static retraction group presented more frequently with postoperative dysphagia as compared with those in the dynamic retraction group, the type of retractor used in each patient was not prospectively randomized in this study and was chosen on the basis of surgeon preference. This introduced bias to the study. Furthermore, the patients in the dynamic retraction group were significantly older than those in the static retraction group by almost a decade. Although increasing age has been previously suggested to be a risk factor for postoperative dysphagia27, our findings point in the opposite direction in as far as the younger group (the static retractor group) had a higher prevalence of dysphagia. This interesting incidental finding requires further research because both groups were comparable in terms of factors other than age, including body mass index, the duration of surgery, the number of surgical levels, average perfusion, and peak and average intraluminal pressures. Perhaps intermittent retraction has a less deleterious effect than static retraction, in spite of similar time, pressure, and perfusion characteristics. This idea requires additional study.
In conclusion, the findings of the present study suggest that the development of postoperative dysphagia is related to increased retractor pressure during anterior cervical arthrodesis. Decreased mucosal perfusion was also observed concomitantly. Nevertheless, the present study was not designed to demonstrate cause and effect. Future research should include postoperative esophageal electromyography as well as the analysis of biopsy specimens from the esophageal walls to define the pathophysiology of this complication. 
Note: The authors wish to acknowledge the following collaborators: Yubo Gao, PhD; Young-Jin Chang, MD; Judy Swafford, RN; and Barbara Farrell, RA.
Cloward RB. The anterior approach for removal of ruptured cervical disks. J Neurosurg.1958;15:602-17.15602Â
1958Â
[PubMed][CrossRef] Â
Winslow CP, Winslow TJ, Wax MK. Dysphonia and dysphagia following the anterior approach to the cervical spine. Arch Otolaryngol Head Neck Surg.2001;127:51-5.12751Â
2001Â
Â
Stewart M, Johnston RA, Stewart I, Wilson JA. Swallowing performance following anterior cervical spine surgery. Br J Neurosurg.1995;9:605-9.9605Â
1995Â
[CrossRef] Â
Martin RE, Neary MA, Diamant NE. Dysphagia following anterior cervical spine surgery. Dysphagia.1997;12:2-10.122Â
1997Â
[CrossRef] Â
Lee SK, Lee GY, Wong GT. Prolonged and severe dysphagia following anterior cervical surgery. J Clin Neurosci.2004;11:424-7.11424Â
2004Â
[CrossRef] Â
Bazaz R, Lee MJ, Yoo JU. Incidence of dysphagia after anterior cervical spine surgery: a prospective study. Spine.2002;27:2453-8.272453Â
2002Â
[CrossRef] Â
Riley LH 3rd, Skolasky RL, Albert TJ, Vaccaro AR, Heller JG. Dysphagia after anterior cervical decompression and fusion: prevalence and risk factors from a longitudinal cohort study. Spine.2005;30:2564-9.302564Â
2005Â
[CrossRef] Â
Yue WM, Brodner W, Highland TR. Persistent swallowing and voice problems after anterior cervical discectomy and fusion with allograft and plating: a 5- to 11-year follow-up study. Eur Spine J.2005;14:677-82.14677Â
2005Â
[CrossRef] Â
Lee MJ, Bazaz R, Furey CG, Yoo J. Influence of anterior cervical plate design on dysphagia: a 2-year prospective longitudinal follow-up study. J Spinal Disord Tech.2005;18:406-9.18406Â
2005Â
[CrossRef] Â
Wong DT, Fehlings MG, Massicotte EM. Anterior cervical screw extrusion leading to acute upper airway obstruction: case report. Spine.2005;30:E683-6.30E683Â
2005Â
[CrossRef] Â
Morpeth JF, Williams MF. Vocal fold paralysis after anterior cervical diskectomy and fusion. Laryngoscope.2000;110:43-6.11043Â
2000Â
[CrossRef] Â
Bulger RF, Rejowski JE, Beatty RA. Vocal cord paralysis associated with anterior cervical fusion: considerations for prevention and treatment. J Neurosurg.1985;62:657-61.62657Â
1985Â
[CrossRef] Â
Apfelbaum RI, Kriskovich MD, Haller JR. On the incidence, cause, and prevention of recurrent laryngeal nerve palsies during anterior cervical spine surgery. Spine.2000;25:2906-12.252906Â
2000Â
[CrossRef] Â
Beutler WJ, Sweeney CA, Connolly PJ. Recurrent laryngeal nerve injury with anterior cervical spine surgery risk with laterality of surgical approach. Spine.2001;26:1337-42.261337Â
2001Â
[CrossRef] Â
Audu P, Artz G, Scheid S, Harrop J, Albert T, Vaccaro A, Hilibrand A, Sharan A, Spiegal J, Rosen M. Recurrent laryngeal nerve palsy after anterior cervical spine surgery: the impact of endotracheal tube cuff deflation, reinflation, and pressure adjustment. Anesthesiology.2006;105:898-901.105898Â
2006Â
[CrossRef] Â
Heese O, Schroder F, Westphal M, Papavero L. Intraoperative measurement of pharynx/esophagus retraction during anterior cervical surgery. Part I: pressure. Eur Spine J.2006;15:1833-7.151833Â
2006Â
[CrossRef] Â
Heese O, Fritzsche E, Heiland M, Westphal M, Papavero L. Intraoperative measurement of pharynx/esophagus retraction during anterior cervical surgery. Part II: perfusion. Eur Spine J.2006;15:1839-43.151839Â
2006Â
[CrossRef] Â
McHorney CA, Ware JE Jr, Raczek AE. The MOS 36-Item Short-Form Health Survey (SF-36): II. Psychometric and clinical tests of validity in measuring physical and mental health constructs. Med Care.1993;31:247-63.31247Â
1993Â
[CrossRef] Â
Ware JE Jr, Kosinski M, Keller SD. SF-36 physical and mental health summary scales: a user's manual. Boston: The Health Institute, New England Medical Center; 1994.Â
1994Â
Â
Chen AY, Frankowski R, Bishop-Leone J, Hebert T, Leyk S, Lewin J, Goepfert H. The development and validation of a dysphagia-specific quality-of-life questionnaire for patients with head and neck cancer: the M.D. Anderson dysphagia inventory. Arch Otolaryngol Head Neck Surg.2001;127:870-6.127870Â
2001Â
Â
Smith GW, Robinson RA. The treatment of certain cervical-spine disorders by anterior removal of the intervertebral disc and interbody fusion. J Bone Joint Surg Am.1958;40:607-24.40607Â
1958Â
Â
Frempong-Boadu A, Houten JK, Osborn B, Opulencia J, Kells L, Guida DD, Le Roux PD. Swallowing and speech dysfunction in patients undergoing anterior cervical discectomy and fusion: a prospective, objective preoperative and postoperative assessment. J Spinal Disord Tech.2002;15:362-8.15362Â
2002Â
[CrossRef] Â
Schindler JS, Kelly JH. Swallowing disorders in the elderly. Laryngoscope.2002;112:589-602.112589Â
2002Â
[CrossRef] Â
Ikeda Y, Niimi M, Kan S, Shatari T, Takami H, Kodaira S. Clinical significance of tissue blood flow during esophagectomy by laser Doppler flowmetry. J Thorac Cardiovasc Surg.2001;122:1101-6.1221101Â
2001Â
[CrossRef] Â
Hilibrand AS, Artz GJ, Vaccaro AR, Albert TJ, Audu P, Rosen M. Vocal fold paralysis after anterior cervical spine surgery: A prospective, randomized, double-blinded study. Read at the Annual Meeting of the Cervical Spine Research Society; 2005 Dec 1-3; San Diego, CA.Â
2005Â
Â
Urschel JD, Antkowiak JG, Takita H. Gastric distention exacerbates ischemia in a rodent model of partial gastric devascularization. Am J Med Sci.1997;314:284-6.314284Â
1997Â
[CrossRef] Â
Smith-Hammond CA, New KC, Pietrobon R, Curtis DJ, Scharver CH, Turner DA. Prospective analysis of incidence and risk factors of dysphagia in spine surgery patients: Comparison of anterior cervical, posterior cervical, and lumbar procedures. Spine.2004;29:1441-6.291441Â
2004Â
[CrossRef] Â