Despite increases in use, information on comparative perioperative complication rates after ACDF and PCDF procedures remains rare. Because there is a subset of patients in whom either of the two approaches would appear reasonable, data assessing perioperative risk are essential to decision-making. The purposes of this study were to (1) characterize the patient population undergoing ACDF and PCDF; (2) compare perioperative complication rates; (3) determine independent risk factors for adverse perioperative events; and (4) aid in surgical decision-making in cases in which clinical equipoise exists between anterior and posterior cervical fusion procedures.
There are several limitations to our study. First and most importantly, the NIS database, designed primarily for administrative purposes, does not include complete information on pathoanatomic features of spondylosis or trauma, number of affected levels and patterns of disease, number of levels fused, the sagittal cervical spine alignment, or detailed clinical information (ie, length of surgery, blood loss, etc). Second, the indication for surgery using ICD-9 codes within this data set is speculative at best, because no defined variable for surgical indication exists in the NIS. As a result, although our multivariate regression analysis controlled for comorbidity index and demographic features, we could not distinguish patient populations based on these relevant surgical factors. Therefore, there is likely still bias injected into the analysis because current practice trends and surgical decision-making still favor using posterior fusion for constructs of three or more segments, making the PCDF group likely to have more extensive disease. Furthermore, our analysis includes a heterogeneous group of cervical spondylosis, trauma, and other diagnoses resulting in the need for fusion. Third, because the data are compiled only for inpatients, actual complication and mortality rates may be higher and our data should be interpreted in this context. The literature suggests PCDF wound complications (as a result of late presentation at initial followup) may be slightly higher than that captured here [9
]. Further, the database does not allow for reliable distinction of major from minor complications. Finally, parameters such as fusion rates, late reoperation, sagittal alignment, adjacent level disease, and late clinical outcomes are not included here. ACDF surgeries are associated with decreasing fusion rates as the number of segments or instrumented levels increases. Recent advances in anterior plating techniques, however, have led to a 96% fusion rate in three-level ACDF with an anterior plate [24
]. Others have reported an average fusion rate of 93% for four-level ACDF with an anterior plate [5
]. Posterior cervical instrumented fusion rates have ranged from 95% to 100% in the literature [7
]. However, concerns persist about loss of cervical lordosis in the posterior cervical spine surgical patients [4
]. Additional considerations include a 2.9%/year incidence of clinically important adjacent segment disease among ACDF patients versus a 1%/year incidence in posterior cervical fusion patients [28
]. Although considered important, other limitations not listed here are those inherent to secondary analysis of large administrative databases, including but not limited to its retrospective nature and potential coding bias.
Demographics associated with ACDF and PCDF differed. The PCDF group was older and consequently had more medical comorbidities, it tended to be performed more frequently among male patients, and it occurred more often in a trauma setting and in large urban, teaching centers rather than small rural nonteaching hospitals. One obvious explanation for the age discrepancies is the increased reliance on posterior fusion procedures in the setting of multilevel cervical spondylosis—an entity more commonly seen in an elderly patient population. By the same token, increased prevalence of trauma patients among the posterior fusion group is reflective of biomechanical requirements and practice preferences in the trauma setting. Often, traumatic injuries of the cervical spine represent three-column injuries. This can be initially stabilized by an all posterior construct. Furthermore, rapid decompression and the establishment of long, stable constructs is the primary objective in acute trauma—thereby favoring posterior fusions in this group [23
]. Overall patient age and comorbidity burden has increased among all patients undergoing cervical fusion over time in both anterior and posterior groups [8
We found PCDF procedures were associated with increased rates of in-hospital complications and mortality compared with ACDF procedures. The in-hospital mortality rate for ACDF procedures seems to have decreased from the period of 1988 to 2003 when compared with that encompassing the years 1998 to 2006 (0.57% to 0.26%) (Table ). At the same time, postoperative mortality rate for the PCDF increased from 1.03% to 1.45% between the two data sets, perhaps reflective of the shift in age and comorbidities [29
]. Furthermore, the PCDF group had a higher incidence of immediate postoperative wound complications, recognized implant or hardware failure, and longer hospital stay. This is an important finding because postoperative complications, the need for revision surgery, and the length of hospital stay have been identified as major factors determining overall hospital cost [15
]. Although an important issue, cost analysis was beyond the scope of this particular study.
Studies comparing outcomes after ACDF and PCDF over time
When controlling for patient comorbidity burden and demographic factors, we found PCDF was an independent risk factor for postoperative mortality (odds ratio 2.01; confidence interval 1.64–2.49). Additional risk factors were male gender and advanced age. Comorbidities increasing the risk for perioperative death included pulmonary circulatory disease, renal disease, cancer, coagulopathy, congestive heart disease, or myelopathy. Although PCDF has not been identified as a risk factor previously, the other factors are associated with such risk in other orthopaedic surgical setting in the past [21
]. Patients with pulmonary circulatory disease may represent an especially vulnerable group because perioperative insults such as mechanical ventilation and embolization of bone marrow and debris during the instrumentation process may aggravate right heart dysfunction and its sequelae. Intensive perioperative care and other advanced services should be available to optimize perioperative safety in these challenging patients. Interestingly, a number of comorbidities, including liver dysfunction and diabetes, did not alter perioperative mortality despite being associated with an overall increased perioperative morbidity [3
We identified PCDF to be associated with increased rates of perioperative morbidity and mortality and as an independent risk factor for in-hospital death when compared with ACDF procedures. Despite the limitations, this data set offers clinicians an important insight into the impact of either anterior or posterior fusion procedures on their patients. Rather than dictating surgical decision-making, this information is important for managing surgeon and patient expectations on risk, hospital course, and immediate postoperative complications. In terms of surgical decision-making, there remains a subset of patients with cervical disease in whom clinical equipoise exists as to whether they should be treated with an anterior versus posterior cervical fusion after considering such factors as diagnosis, diseased levels, stenosis type, and sagittal alignment [12
]. Traditional dogma has suggested elderly patients do not tolerate multilevel anterior surgery [2
] and has cautioned against multilevel ACDF exceeding three segments. However, implant improvements (especially improved anterior plating systems) have given reason to rethink some of these paradigms [5
]. As a result, there is still a need in the literature for prospective diagnosis and age-matched cohort analysis to determine relative risks for postoperative complications such as mortality, wound complications, and prolonged hospital stay between anterior versus posterior fusion. These “pure” matched cohorts would then enable us to make the best possible decision for these patients who fall “in between” the clear established criteria for anterior versus posterior approach to cervical pathology.