While very common in the initial postoperative period, the natural history of dysphagia usually involves amelioration or resolution within the first year. Bazaz et al. (5) examined patients at 1, 2, 6, and 12 months postoperatively using the dysphagia scoring system of the authors’ design. At 1 month, 50.3% (99/197) of patients demonstrated dysphagia, but only 5.6% (11/197) were severely affected. At 6 months, the number reporting swallowing difficulty fell to 17.7% (37/208). Finally, at 1 year, only 12.5% (19/152) exhibited dysphagia. Smith-Hammond et al. (6) also found that the majority (71%) of those with difficulty swallowing in the first several days postoperatively returned to a regular diet within 2 months. These findings suggest that surgeons can expect approximately 50% of patients to demonstrate some difficulty with swallowing in the immediate postoperative period, followed by a steady rapid improvement such that only about 10% experience dysphagia at 12 months.

Long-term studies of persistent dysphagia are rare, though research by Yue et al. (7) on 74 patients found that dysphagia not resolving by 12 months may persist throughout a patient’s lifetime. Though swallowing difficulty often resolves after 6 to 12 months, continued dysphagia may not resolve after this point.

Dysphagia may be associated with a myriad of risk factors that are poorly understood. Bazaz et al. (5) found female gender (at 6 months) and multiple-level surgery (at 1 month) to be statistically significant risk factors; age, revision surgery, surgery type (corpectomy vs. discectomy), and hardware placement were not found to be factors. Furthermore, multiple-level surgery and the duration of presurgical pain were found to be risk factors by a retrospective analysis of 454 patients by Riley et al. (8). Smith-Hammond et al. (6) found only age to be a risk factor, and no surgical variables (including instrumentation) were found to be statistically significant factors. Thus, the range of risk factors is incomplete and worthy of further investigation, but potential factors include age, female gender, multiple-level surgery, and preexisting swallowing dysfunction. Notably, insertion of a surgical plate has not been demonstrated to be a risk factor for postoperative dysphagia.

Several potential causes may contribute to postoperative dysphagia, though the exact pathologic mechanism remains elusive (9,10). In cases of postoperative dysphagia, the possibilities of recurrent laryngeal nerve (RLN) palsy, of a developing hematoma, of prominent hardware, of dislodged graft and instrumentation, and of soft tissue swelling should be ruled out in a timely manner. Only after these common causes of dysphagia are ruled out can consideration be given for a surgical solution to the problem.

One potential cause of swallowing dysfunction is vocal cord paresis due to injury of the RLN, which occurs after anterior cervical discectomy in 0.07% to 11% of cases (11). Damage can be a result of numerous factors affecting the nerve: compression, blunt trauma, nerve division or ligature, stretch-induced neuropraxia, or postoperative edema. Notably, a recent series by Jung et al. (12) found that 16% of their patients undergoing anterior cervical discectomy and fusion (ACDF) developed clinically silent RLN palsy postoperatively, as determined by direct laryngoscopic examination. This finding is critical since a patient with unilateral RLN palsy, though not clinically apparent, risks suffering a devastating bilateral RLN palsy if a second neck operation is performed on the contralateral side. Use of careful, periodically released handheld retraction as opposed to traditional retraction has been suggested as a mechanism to reduce RLN palsy (9).

Controversy also surrounds the importance of a rightversus a left-sided approach to the anterior cervical spine in preventing RLN palsy. Tew and Mayfield (13) initially suggested that the left RLN might be less susceptible to injury during cervical surgery than the right on account of its longer, more predictable, and more protected route looping around the aortic arch. While a retrospective study of the otolaryngology literature indicated a higher rate of aspiration/dysphagia with a right-sided approach, larger studies have reported low rates of RLN injury after use of a right-sided cervical approach (12,14). A critical study by Kilburg et al. (15) found no statistical difference in the rate of RLN injury comparing right- and left-sided approaches in a retrospective review of 418 patients undergoing one- and two-level instrumented ACDF. Thus, sufficient evidence does not exist presently to advocate one approach versus another based on current literature.

Another factor of considerable importance for RLN palsy management is the pressure of the endotracheal (ET) tube. Minimizing pressure on the airway and surrounding tissue is critical since studies have shown that pressure less than 25 mm Hg ensures blood flow through capillary beds (16). Errant placement of an ET tube can lead to vocal cord paralysis by placing excessive pressure on the nerve and its surrounding tissues, leading to potentially irreparable damage. In a cadaveric study of the these effects on the RLN, Apfelbaum et al. (14) noted that pharyngeal tissues adjacent to the ET tube were subject to significant compression, with the ET tube pressure rising threefold with the introduction of deep retractors that further compress the tissues. To prevent this, the group lowered the ET tube pressure to a “just sealed pressure” of 15 mm Hg after placement, thereby allowing tube relocation but still preventing air leak. Application of the paradigm to 900 consecutive patients demonstrated a decreased paralysis rate of 1.7% using the proposed ET technique to 6.4% control (14). A recent prospective study by Audu et al. (17), however, failed to demonstrate a comparable drop in the incidence of postoperative vocal cord immobility by performing an ET tube deflation and maintaining a pressure of 20 mm Hg intraoperatively. Though questions remain, maintaining a reduced ET pressure is nonetheless advised to prevent subsequent dysphagia.