It was estimated that the percentage of patients undergoing lumbar interbody fusion for degenerative spondylolisthesis increased from 13 % to more than 30% between 1999 and 2011.[10] Recently, there has been a significant increase in use of lumbar interbody fusion, and this was accompanied by an increase in the age and number of comorbidities in patients undergoing this procedure. [17,22] Therefore, post-operative morbidity and mortality measures of lumbar fusions have been the focus of recent research.[35,18]
Specialty training is considered an important provider-side variable driving differences in comparative effectiveness between surgeons [8]. The effect of surgeon specialty on outcomes of spinal fusion surgeries has been examined by several studies [18,31]. A recent study conducted on MarketScan database[15] included patients undergoing lumbar laminectomy or lumbar fusion surgeries, reported that lumbar fusion cases operated by neurosurgeons have slightly higher odds of experiencing any complication (OR, 1.1) and higher revision surgery rate (OR, 1.14), however, this study was limited by reporting the bivariate logistic regression results only and without adjusting for any potential confounding through multivariate logistic regression, despite the fact that the patients in the neurosurgery cohort where significantly more comorbid than the orthopedic cohort [15]. Other studies concluded that spine surgeon specialty is not a risk factor for any of the reported postoperative complications in patients undergoing spinal fusions except for the observed higher rate of perioperative blood transfusion [18,31], and slightly higher odds for prolonged length of stay among orthopedic surgeons [31]. Similar to previous reports in the spine literature [18,31], our analysis showed that PLIF/TLIF patients operated by orthopedic surgeons were more likely to receive perioperative blood transfusion when compared to similar patients operated by neurosurgeons. Moreover, while a previous study [31] reported that patients undergoing spinal fusions have slightly higher odds for prolonged length of stay among orthopedic surgeons, our study added that PLIF/TLIF patients operated by orthopedic surgeons were more likely to have higher return to operating room rates within the same admission, be discharged to destination other than home, be discharged after postoperative day 3, and higher readmission rates.
The differences in results between our current study and previous studies might be explained by several reasons. It is worth mention that previous studies have been limited by significant heterogeneity since they included different spinal fusion levels (cervical, thoracic and lumbar), number of operative levels, and surgical techniques in the same analysis [18,31]. In contrast, we included a homogenous cohort of patients undergoing PLIF/TLIF for degenerative spine disease and we further stratified the cohort into single- and multi-level groups to account for these limitations in previous reports. In addition, previous studies did not control for the preoperative functional health status (independent / dependent), and surgery status (elective/emergency) [18] which several studies showed that they have significant effect on the outcomes [13]. In fact, our analysis on patients undergoing PLIF/TLIF showed that patients operated on by neurosurgeons were significantly more likely to be dependent and that being dependent predicts worse outcomes, Tables (1, 4). Therefore, adjusting for such confounding variables are important to avoid biased results. We also limited our cohort to elective surgeries to avoid the confounding of this variable that was present in previous reports.
These differences between the cohorts might be attributed to different trends in spine surgery training during neurological and orthopedic surgery residencies. Although both residency specialties are exposed to subspecialty spine training, the length of training as well as the level of exposure of spinal pathology itself have been found to vary greatly.[5,14,21,34,30] A recent study [20] included a ten-year analysis of ACGME case log data and found that case volume of spine surgery procedures is significantly larger for neurological surgery residencies when compared to the orthopedic counterparts. Moreover, they found that this discrepancy in case volume is enlarging over time, [20] which might explain that these differences between the 2 cohorts were apparent in our updated analysis, while they were not present in previous similar studies. Despite that case volume alone cannot solely determine the quality of training, it is considered one of the key measures to assess opportunities to develop optimal surgical education[20]. Another study [6], which evaluated self-assessed surgical competence of senior neurosurgery and orthopedic residents by mail-out questionnaire, concluded that neurosurgery residents graduate with a significantly higher level of confidence to perform spine surgery (which included cervical and lumbar fusions), while orthopedic residents report significantly higher need for additional training in spine surgery.
Moreover, our study showed that nationally, nearly 2 times as many PLIF/TLIF procedures are performed by neurosurgeons than orthopedic surgeons. One possibility is that ACS-NSQIP database includes cases from larger or academic institutions [18,19] that might employ more neurosurgeons who perform spine procedures than orthopedic surgeons.
Although the reasons behind these differences between the two cohorts remain largely unknown and might be beyond the scope of this study, it is worth mentioning that these outcome measures might have significant clinical and cost implications for patients, physicians, program directors, hospitals and payors [28,37,27,1]. The higher incidence of blood transfusion among orthopedic cohort is of interest since it may represent a potentially modifiable practice. Purvis et al reported that higher perioperative blood transfusion might be associated with increased morbidity in patients undergoing spine surgery and that modification of transfusion practice may be a potential area for improving patient outcomes and reducing costs [25,24]. This is concordant with a study by Corwin et al which concluded that packed red blood cell transfusion is an independent risk factor for increase in patient morbidity, mortality, and length of stay [4]. In addition, a more recent institutional study showed more than $2 million savings when packed red blood cell transfusions were decreased by one third.[23] Shields et al [32] recently demonstrated that each hour of decreased length of hospital stay following lumbar fusion directly correlated with cost savings. Moreover, Hydrick et al found that 90-day readmissions were associated with an average of $96 152 in increased hospital costs per patient following lumbar fusion [7].
Overall, focused studies are encouraged in the future to address potential reasons and possible solutions for these differences between the two cohorts.
Limitations:
The retrospective design of the study is a major limitation. In addition, selection bias, confounding and reliability of data collection remain potential concerns. However, a strict propensity score matching (match tolerance of 1%) was applied to minimize bias and confounding of different variables, yielding similar, matched cohorts, and improving the internal validity of the paper. The ACS-NSQIP database provides data with high rates of inter-rater reliability and validation sets performed. Per NSQIP, audit reports have revealed an overall disagreement rate of less than 2% [9,33,11]. The ACS-NSQIP database does not include data on skill level of individual surgeons, such as years in practice, which may have an effect on the outcome. Moreover, the ACS-NSQIP database does not include several variables of interest specific to neurosurgery, including postoperative symptom relief, rates of neurological complications, such as postoperative sensory loss, weakness, or cerebrospinal fluid leak, and outcomes beyond the 30-day postoperative period. Finally, although ACS-NSQIP covers a broad base of hospitals –more than 700 hospitals-, only a fraction of hospitals participates in ACS-NSQIP, which might limit the (external validity) generalizability of these data.