CORR Insights®: Minimum Clinically Important Differences of the Hospital for Special Surgery Dysphagia and Dysphonia Inventory and Other Dysphagia Measurements in Patients Undergoing ACDF

Where Are We Now? The number of anterior cervical spine operations in the United States is rising, with a 206% increase of use from 1992 to 2005 as reported among Medicare recipients [1, 11]. There has also been a national trend toward a greater utilization of the outpatient environment and same day operations. As such, it is crucial that we better understand the early complications following anterior cervical spine operations, such as anterior discectomy and fusion [12]. Dysphonia and dysphagia are known complications following anterior cervical procedures, but the frequency with which these complications occurs varies widely. For example, postoperative dysphagia occurs after 2% to 60% of patients who undergo anterior cervical discectomy and fusion [13]. Still, these postsurgical complications occur frequently enough that 68% of the 115 survey respondents from the Cervical Spine Research Society reported dysphagia as an expected and acceptable surgical complication [11]. To echo this sentiment, dysphonia and dysphagia are, in my experience, part of the preoperative discussions of most spinal surgeons and are presented, in at least some form, as something a patient should expect after surgery. The magnitude and duration of dysphonia and dysphagia after surgery are therefore pertinent to almost all patients, but these certainly are a greater concern for patients who are at increased risk, such as patients with multiple levels of surgery, longer durations of surgery, surgeries that are very cranial or caudal. A critical limitation of studies that evaluate dysphonia and dysphagia after anterior cervical discectomy and fusion is the lack of a validated, quantitative, easy to use, and universally accepted measures of dysphonia and dysphagia. For that reason, the current study by Okano et al. [6] is so important. This study determined the minimum clinically important difference (MCID) for the Hospital for Special Surgery Dysphagia and Dysphonia Inventory (HSS-DDI) to be 11 of 100 points for the distribution-based approach and 9 of 100 points for the anchor-based approach [6]. The two accepted methods to determine MCID the authors chose were the distribution-based approach (in which measurement error drives the minimal detectable change) as well as an anchor-based approach (which uses an independent external anchor question with good face validity, and which clinicians and patients believe would reasonably be responsive the presence or absence of symptoms [3]). Anchor-based approaches may be both more familiar and more helpful to clinicians, as they consider whether observed effects in a research study are large enough to care about [4]. Where Do We Need To Go? We still don’t know the actual prevalence (as mentioned, estimates vary widely, and likely depend largely both on patient and surgical factors) and impact of dysphonia and dysphagia both in the early postoperative course and over the long-term. As reported by the authors of the current study, one of the most used outcome measures is the utilization of the Bazaz scale [2], which, while easy to use, only includes four grades and only examines reported swallowing difficulty. Although it is easy to administer, the Bazaz scale is not a qualitative measure of swallowing difficulty. Indeed, surgeons simply do not adequately address the issue. Dysphonia and dysphagia concerns are often not asked about to the extent that they should be during the postoperative course, leaving unanswered questions concerning duration and severity. Developing a way to ascertain quantitatively the impact of dysphonia and dysphagia is essential. While the HSS-DDI is a quantitate method, it has yet to be proven as a tool that is easy to administer and that is widely accepted. Independent testing is necessary as well as wide spread adoption. Unless multiple centers and studies adopt this system, the ability to pool and compare these studies is limited. The spine community must select a comprehensive and validated dysphonia and dysphagia assessment and utilize it universally for us to be able to best advise patients and identify modifiable surgical risks and techniques. How Do We Get There? While a distribution-based approach is very analytical, it fails to qualitatively address the outcome. Still, an anchor-based approach depends on the qualitative determination of what a meaningful anchor measure is. The authors effectively reported both values for the HSS-DDI. However, the current study was performed at the institution that developed the tool, by authors who created the outcome measure. As with all novel measures, outside validation will be necessary. The next steps must include applying this assessment and these metrics to an independent population or series of populations. While patient-reported outcome measures provide independent and validated information on aspects of the satisfaction of our patients, the measures themselves are numerous and the practicality of administering a litany of questionnaires needs to be assessed. What questions are important to ask our patients? Likely this will require administering these robust question sets to a large population of patients such as a nationally collected spine registry. The North American Spine Society as well as the American Spine Registry are two such registries that may be able to fill this void. Once enough data is collected, patterns can be assessed that may allow us to determine what needs to be asked. Computer adaptive testing efforts such as Patient-Reported Outcomes Measurement Information System have already made some headway. Once a reliable, validated, and nonburdensome measurement method has been realized, the true impact of dysphonia and dysphagia can be more meaningfully assessed and monitored. Additionally, risk factors that have been identified in smaller previous studies (such as, a history of obstructive sleep apnea, asthma, female sex, age more than 60 years, smoking status, prior cervical surgery, and postoperative soft-tissue edema) can be either confirmed or refuted [2, 5, 7-10]. Measures like the HSS-DDI may also allow for the investigation of surgical techniques that surgeons can modify (such as, device selection, surgical approach, number of levels operated, use of rhBMP-2, duration of surgery, and use of steroids), which may reduce the impact of these important symptoms on patients’ recoveries from anterior cervical spine surgery.