As medicine, economies and technologies have continued to advance, aging of the population also has accelerated tremendously in the past decades, and there has been a marked reduction of fertility and an extension of life expectancy world-wide . As a consequence, the elderly population (older than 60 years old) has boomed from approximately 200 million in the world 60 years ago to approximately 600 million by the beginning of the twenty-first century. The growth of an aging population has been exponential in recent past years, and this rate of acceleration was estimated to be 3.5 times faster than that of the entire population . One of the major issues of aging has been the remarkable burden of degenerative spinal disorders among the elderly, causing not only back problems but also cervical spondylosis. For example, in one national database, the utilization of anterior cervical procedures had a 28-fold increase for persons 65 years and older during a 15-year period at the end of the last century . The increasing need of surgical care in cervical spine degenerative disease is real and imminent. However, there has been a paucity of literature that has focused on the outcomes of cervical spinal surgery among the geriatric population.
The current study focused on a comparison of patients at both ends of the age distribution (≧65 or ≤ 40 years) in a cohort of CDA patients. Patients who had been followed-up for more than 24 months were included for retrospective analysis of their clinical outcomes (i.e. VAS, NDI, and JOA scores), radiological parameters (i.e. pre-, post-operative ROM, and incidences of HO), and the complication profiles (e.g. dysphagia, dysphonia, and C5 palsy). The study demonstrated small but distinct discrepancies between the elderly and young in the changes of segmental mobility after CDA. More than 2 years after 1- or 2-level surgery for CDA, both groups of patients, regardless of their age differences (i.e. elderly versus young), demonstrated improvements in clinical outcomes when compared to that of pre-operation. Moreover, both groups had successfully preserved segmental mobility at the indexed levels with CDA.
However, in the current study, the most significant differences between the elderly and the young was their segmental mobility. Prior to the CDA surgery, the elderly patients had slightly less ROM than the young. After the CDA, the discrepancy had been magnified even more. The young group had increased ROM compared to that of pre-operation, while, in contrast, the elderly group had a slightly decreased ROM. Although the ROM was still mobile at an average of 5.6° for the elderly, the young group of patients were more mobile with an average ROM of 8.3°.
Also, the incidences and severity of the HO in both age groups were not significantly different. The complication profiles were also very similar among the elderly and young patients.
This paper demonstrated that the application of CDA in the elderly had similar clinical outcomes to the young patients, and thus implied that CDA could be a viable and effective option for patients greater than 65 years old. For the young patients (≤40 years) who needed surgical management for 1- or 2-level cervical disc herniation or spondylosis, CDA would very likely achieve good outcomes and preserve segmental mobility that would be even greater than the elderly group.
There have been many FDA-IDE trials of CDA on 1- and 2-level cervical disc herniation or spondylosis that caused radiculopathy, myelopathy, or both. The trials unanimously demonstrated that CDA was as safe and effective as ACDF in the improvement of neurological symptoms, while superior in preservation of the segmental mobility than ACDF. These trials were commonly designed to enroll adult patients 18 to 78 years old and had mean ages of enrolled subjects around the mid-forties (averaged approximately at 45 years for all studies) [4,5,6, 13, 30]. However, none of them had investigated the detailed age-related differences, and it remained elusive as to the various effects of CDA among the elderly patients than the younger patients. Although there had not been reports against the use of CDA in patients over 65 years, it has been unclear if these elderly patients do as well as those patients under 40 years of age. Probably the most common concerns against using CDA among the elderly were the risks of complications and the lack of economic efficiency because the elderly patients have a shorter life expectancy than the younger patients. Nevertheless, several FDA-IDE trials had pushed the border of the surgery to use CDA in patients older than 70 years [2, 3, 8, 31].
Ideal candidates of CDA are young patients who have soft disc herniations and little degeneration in the facet joints, and it is commonly accepted that young patients benefit more from CDA because it provides them with more years of neck mobility than ACDF. Reports on CDA in the literature have had various inclusion criteria for age. For instance, the RCTs for Kineflex-C (SpinalMotion, Inc), ProDisc-C (Depuy-Synthes, Inc), and PCM (Nuvasive, Inc) trials set the limitation of age for inclusion to be < 60 or < 65 years old [4, 5, 10]. The Mobic-C (Zimmer-Biomet, Inc) trials allowed patients equal to or less than 69 years old [7, 30]. The clinical trials for Prestige and Bryan (Medtronic, Inc) included patients no older than 78 years [2, 3, 31]. Despite the wide range of age inclusion in these large-scale prospective trials, the mean age of patients enrolled was around 43 to 46 years. In the current study, the two groups had similar demographics, except the distinct differences in their mean ages [71.2 (65-80) versus 33.9 (23-39) years, elderly versus young, respectively]. The study provided a direct comparison of patients of different ages undergoing CDA surgery, and attempted to differentiate the age factor, filling the information gap in the randomized control trials of the FDA mentioned above.
Older age could be associated with cardiopulmonary complications in major surgery but not necessarily with anterior cervical spine surgery. There was one study which utilized the American College of Surgeons’ National Surgical Quality Improvement Program (ACS-NSQIP) database to analyze the complications after ACDF. It demonstrated that, by multivariate logistic regression, aging was associated with pulmonary complications, UTI, cardiac complication, and sepsis . There was also another large cohort study that revealed similar findings for older patients undergoing ACDF . However, in the current study and the FDA trials, there were few cardio-pulmonary or infectious complications. Perhaps the most common complications of anterior cervical spine are dysphagia, dysphonia, and temporary C5 palsy. Likewise in the series, dysphagia accounted for the most common complication at approximately 12 and 2% in the elderly and young groups, respectively. Dysphonia accounted for 4.2 and 2.1% in each of the two groups, respectively. These incidences were comparable with the mean incidences of dysphagia and dysphonia combined from the FDA trials, which ranged from 4.73 to 17.33% . Due to the lack of operational definition and severity of dysphagia, the prevalence varied among different studies. It was reported that patients of old-age (> 70) had a 4.96-times higher risk of severe dysphagia after ACDF in a nationwide-scaled database . There were few data available in the literature for CDA, especially for the elderly recipients. The current report also merits the addressing of these rates of complications after CDA in the elderly. There were only temporary dysphagia and dysphonia in the elderly patients in the series and they were all resolved spontaneously within 6 months.
It might be intuitive to expect higher complication rates for elderly than younger patients who undergo surgery, but this was not the case in anterior cervical discectomy. In the current series of CDA, the complication rates were very similar for the elderly and young patients. There was one patient (2.1%) in the elderly group who developed unilateral C5 palsy after CDA, while there was no C5 palsy in the young group. In the FDA trials, neurologically related adverse events were reportedly ranging from 0.4 to 13.4% in different trials in gross, but the details were not disclosed in the paper . For anterior cervical fusion, the risks of C5 palsy varied from 3 to 17%, depending on the levels of discectomy, corpectomy or not, instrumentation, etc . The incidence of C5 palsy specifically after CDA surgery has never been reported or compared to that after ACDF in the trials. In the current series, the incidences of adverse events in the elderly patients who underwent CDA were similar to that of the young.
The middle-age patients, who were not included in the present study, had very similar outcomes to the elderly and young groups. Those middle-age patients reportedly had common results. For example, one of our previous studies evaluated 50 middle-age patients (mean age 45.6 ± 9.33 years) of 1-level Prestige CDA and demonstrated similar clinical improvements at 24 months after surgery. All the mean VAS, NDI, and JOA scores of the middle age patients improved significantly from 4.4 to 1.8, 15.5 to 8.6, and 13.1 to 14.7, respectively . Furthermore, these results were consistent with that demonstrated in the current study, including all patient-reported outcome parameters (VAS, NDI, and JOA scores) of the elderly and young patients, and unanimously had similar improvements at the final follow-up. Many of our published studies have focused on the most commonly reported middle age groups (with approximately the same mean ages around 45 to 50 years), indicating insignificance from the two extreme age groups, the elderly and young [18,19,20, 22, 37,38,39,40,41].
There are limitations to the current study. The patients were extracted from a cohort of CDA patients treated surgically by the 3 senior authors for analysis. The elderly patients inevitably had a shorter life expectancy than the young and this could be a confounding factor. The length of follow-up can be a weakness for this study. There was a discrepancy in length of follow-up for individual patients. However, average length of follow-up still achieved 22.6 and 30.8 months in the elderly and young group, respectively. The sample size of both groups was small and lacked a control group of ACDF for comparison. Since the age-related discrepancies appeared to be subtle, a larger sample size could be necessary to detect the subtle differences. Furthermore, the criteria of age used for grouping (≥65 and ≤ 40 years old) in the study was arbitrary and might not be the best way for division. However, since we intended to focus on both ends of the age distribution, especially for the performance of CDA in the elderly patients, middle-aged cases (41–64 year-old) were not in the scope of the present study. Besides, the effectiveness of CDA for middle-aged patients has already been well demonstrated in many Class-I FDA trials. Although the demographic data, other than age, of the two groups showed little differences, the less segmental mobility demonstrated in the elderly was possibly related to degeneration and aging. More adjustment of statistics is usually required to reduce the bias and confounders. Also, the slowly on-going problems of aging and degeneration might require decades before they cause symptoms. Those benefits of CDA utilization in the elderly patients could be masked because the young group had less degeneration and thus required longer follow-up. In contrast, there could be some competing bias in the elderly group that might have skewed the data.