Psoas Size Predicts Perioperative Morbidity after Lumbar Spine Surgery

NASS 31st Annual Meeting Proceedings / The Spine Journal 16 (2016) S251–S337 of patients all who had primary lung cancer diagnoses. This included all histological subtypes of lung cancer. OUTCOME MEASURES: The main outcome of interest was overall survival, which was measured from the date of the patient’s scan (MRI or CT) to date of death. For patients who were still alive at the time of analysis, survival was calculated to the most recent documented follow-up. The median survival (in days) along with the corresponding 95% confidence interval were computed for all patients, as well as subsets of interest. Cox proportional hazards regression analyses were done to estimate the hazard ratios and test for differences in the variables of interest. METHODS: Using previously proven methodology, circumferential morphometric measurements were taken of the psoas muscle at the L4 vertebral body. Measurements were taken from spinal CT or MRI at the time of SBRT for metastases. Psoas muscle sizes were ultimately divided into tertiles according to total psoas area. RESULTS: A total of 178 patients with lung cancer spinal metastases were identified. Ninety-eight patients (55%) were males, and 95 (53%) presented with multiple level metastasis. The median survival for all patients was 156 days (95% CI=116–197 days). The associations of overall survival with gender and the number of levels were not significant. However, the association of overall survival with type of scan was significant (p<.001), with patients receiving an MRI having shorter survival compared to patients receiving CT. Psoas muscle area measurements were divided into tertiles, with adjustments accounted for gender differences in muscle size. When considering the total psoas tertiles based on gender only, the difference between the lowest and highest tertiles was significant (p=.033) with patients in the lowest tertile having shorter survival (115 days, 95% CI=85–67) compared to patients in the highest tertile (253.5 days, 95%CI=158–337). In addition, patients in the lowest tertile had significantly (p=.022) shorter survival as compared to the middle and highest tertile combined (188.5 days, 95% CI=127–254). The differences for the total psoas tertiles based on gender and type of scan and ratio of total psoas to vertebral body area tertiles were not significant. CONCLUSIONS: Our results illustrate that morphometric analysis of psoas size may be predictive of survival in patients with lung cancer metastasis to the spine. The other notable statistical finding in this study is that the type of scan available for morphometric analysis showed that patients who had an MRI were at risk with a significantly shorter survival. This may be due to treatment regimens after imaging, including chemotherapy and radiation therapy. We did find that patients who had an MRI compared to CT did have lower mean psoas size. Given the retrospective nature of this study and non-standardized imaging protocols, it will be difficult to account for potential bias that reflects this finding. However, our study does show the potential of morphometric measurements as a surrogate for survival in this specific population. Future multicenter prospective study will be required to fully validate this methodology. In addition, our methods can also be applied toward other cancer subgroups (breast, prostate, GI, etc.) for future study as well. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. http://dx.doi.org/10.1016/j.spinee.2016.07.376

P52. The Effect of Vancomycin Powder on the Rates of Infection and Pseudarthrosis in Lumbar Spine Surgery: A Retrospective Analysis of 453 Patients Sukanta Maitra, MD1, Jordan Kump1, Zach Lee, BS2, Yue Zhang1, Stephen Pehler, MD3, W. Ryan Spiker, MD4, Brandon D. Lawrence, MD5, Darrel S. Brodke, MD5; 1Salt Lake City, UT, USA; 2University of Utah Department of Orthopedics, Salt Lake City, UT, USA; 3University of Utah Orthopedic Center, Salt Lake City, UT, USA; 4University of Utah Orthopaedics, Salt Lake City, UT, USA; 5University Orthopaedic Center, Salt Lake City, UT, USA BACKGROUND CONTEXT: Surgical site infection (SSI) represents a major complication in spine surgery. The application of topical vancomycin powder

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has been shown to effectively reduce SSI’s. Recent in vitro studies have suggested that topical application of lyophilized vancomycin has an inhibitory effect on osteoblast proliferation and differentiation that may adversely affect fusion rates. PURPOSE: The primary purpose of this study was to examine our institution’s overall revision rate for pseudarthrosis before and after the routine use of vancomycin powder in patients undergoing lumbar spinal fusion. Our secondary goal was to determine the infection rate prior to and after the initiation of vancomycin powder into the wound. STUDY DESIGN/SETTING: A retrospective chart review including all patients undergoing lumbar fusion with at least 2 years of clinical follow up. PATIENT SAMPLE: A total of 232 patients were identified in the prevancomycin group with mean followup of 1.5 years and 221 in the vancomycin group with mean followup of 2 years. METHODS: The prevancomycin group (1/2007–12/2008) were compared to the vancomycin group (1/1/2012–12/31/2013) for development of a SSI requiring debridement, return to OR for revision of the prior surgery and data including number of levels fused, use of bone morphogenetic protein (BMP), and use of interbody grafts was recorded. RESULTS: A total of 232 patients were identified in the pre-vancomycin group with mean followup of 1.5 years and 221 in the vancomycin group with mean followup of 2 years. Overall deep infection rate was 9/232 (3.9%) in the pre-vancomycin group and 4/221 (1.8%) in the vancomycin group. There was a significant difference in the use of interbody grafts (p<.001) and BMP use in the prevancomycin group (p<.001). However, no significant difference was noted in the mean levels fused or revision rates due to pseudarthrosis between the two groups. CONCLUSIONS: The use of topical vancomycin powder did not significantly alter our fusion or revision rates despite significantly less use of interbody grafts and BMP in our vancomycin cohort. Further in vivo and in vitro studies are necessary to fully elucidate vancomycin powder’s role in the maturation of a fusion. FDA DEVICE/DRUG STATUS: vancomycin powder (Not approved for this indication). http://dx.doi.org/10.1016/j.spinee.2016.07.377

P53. Psoas Size Predicts Perioperative Morbidity after Lumbar Spine Surgery Hesham Zakaria, MD1, Azam Basheer, MD1, Brent Griffith, MD2, Victor Chang, MD3; 1Henry Ford Hospital, Detroit, MI, USA; 2Henry Ford Health System, Detroit, MI, USA; 3Henry Ford West Bloomfield Hospital, West Bloomfield, MI, USA BACKGROUND CONTEXT: Low back pain is a common disorder, contributing to a large portion of health care costs. With an increase in the frequency of elective lumbar surgery (decompressions and arthrodesis), there is associated with an increase in the frequency of postoperative complications after spinal surgery. With the current focus on cost-efficient health care, it is important to identify patients that are at greater risk of postoperative morbidity and mortality, which may require greater resource utilization. Factors that contribute to a surgeon’s decision regarding patient selection and surgical approach are generally empiric and without the benefit of a validated risk assessment tool. Validated risk stratification tools provide objective data to surgeons to one aspect of a patient’s operative risk (cardiovascular, pulmonary, psychological, etc.), but their utility to spinal surgery is limited, given that the vast majority of spinal procedures are elective and that surgical candidates are generally without any active exacerbations of their medical problems. Ultimately, risk calculations may be insufficient to assess the overall health of a patient, as two patients with the same preoperative risk factors (ie, age, American Society of Anesthesiologists score, comorbidities and disease stage) are often in clearly different stages of health. Surgeons will often “eyeball” a patient to see if they are fit for surgery, and make operative decisions regardless of risk stratification. Recently, the concept of frailty is being introduced as a measure of a patient’s health status. While it is a common endpoint to human senescence, this process is pathologic and has

Refer to onsite annual meeting presentations and postmeeting proceedings for possible referenced figures and tables. Authors are responsible for accurately reporting disclosure and FDA device/drug status at time of abstract submission.

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NASS 31st Annual Meeting Proceedings / The Spine Journal 16 (2016) S251–S337

been shown to be associated with adverse outcomes after surgery. Unfortunately, measuring human frailty relies on subjective assessments and prolonged patient cooperation, which is impractical in application. Surrogate markers of frailty, such as sarcopenia, may be more useful to clinicians. Morphometrics is the measurement of patient attributes that are indicative of sarcopenia, and thus frailty by proxy. PURPOSE: Morphometric analysis has proven utility in predicting postoperative morbidity and mortality following major general, vascular, and transplant surgery. This study evaluates whether morphometrics can be used as a reliable predictor of perioperative morbidity in patients undergoing lumbar spine surgery. STUDY DESIGN/SETTING: This is a retrospective cohort study of patients undergoing lumbar surgery within the Henry Ford Health System (HFHS). We compiled a database of all patients who underwent lumbar surgery (T11 through S1, inclusive) at HFHS from 2013–2014. OUTCOME MEASURES: Primary outcomes recorded included any 90day postoperative complications including: death, unplanned return to surgery, 30- and 90-day hospital readmission, surgical site infection, wound dehiscence, new neurological deficit, deep venous thrombosis (DVT), pulmonary embolism (PE), myocardial infarction (MI), urinary tract infection (UTI), urinary retention, hospital-acquired pneumonia, stroke and prolonged stay (>3 days) in the Intensive Care Unit (ICU). METHODS: Each patient’s preoperative risk factors, including age, diabetes, smoking, CAD, and BMI, were entered into the database. We concurrently measured the circumferential area of each patient’s psoas muscles at L4 and paraspinal muscles at T12 on preoperative axial T2-weighted MRI sequences. To assess differences in demographic and surgical information and morphometric measurements associated with complications, chisquare tests were performed for categorical/binary variables and two sample t-tests for the continuous variables. Chi-square and Kruskal-Wallis tests were performed to assess the association between the tertile measurements and specific complications and total number of complications. Multivariate logistic regression was done to adjust for potential confounders when assessing the relationship between experiencing any complication and psoas tertiles. RESULTS: A total of 395 patients were included for statistical analysis. Of this population, 30% (n=120) had at least one complication, with the most common complication being urinary retention (12%, n=46), followed by surgical site infection (SSI) (9%, n=36) and unplanned readmission within 90 days (9%, n=36). Patients with complications were an average of 3 years older (65.6 vs 62.3, p=.015) and were more likely to be smokers (19% vs 30%, p=.026). Female gender approached significance to having more complications than males (p=.068). No significant association was found for diabetes, CAD, BMI, number of vertebral levels treated, and whether surgery involved instrumentation or was a revision. To evaluate if morphometric measurements of psoas muscle and paraspinal muscles was predictive of morbidity, we divided patients into thirds based on the size of their psoas and paraspinal muscles, with the highest third having the largest muscle sizes and the lowest third having the smallest. Multivariate logistic regression was done to adjust for potential confounders. Patients in the lowest third of psoas size had an odds ratio of 1.70 that they would experience complications as compared to the other two-thirds (95% CI 1.04–2.79, p=.035). This association was especially prominent in male patients, with an odds ratio of 2.42 (95% CI 1.17–5.01, p=.016) of experiencing a postoperative morbidity. Paraspinal muscle size did not show any significant associations with morbidity. CONCLUSIONS: This is the first time that morphometric analysis has been applied in spinal surgery, illustrating that psoas size may be used as a sensitive tool for perioperative morbidity in patients undergoing lumbar spine surgery. After accounting for confounding factors via multivariate regression analysis, all patients with smaller psoas muscle sizes were significantly more likely to have a postoperative complication. Morphometrics was not successfully applied to females, and the paraspinal muscle groups did not provide any significant data for postoperative morbidity, even after multivariate analysis. Morphometric analysis of psoas size was more sensitive than preoperative risk factors (age, diabetes, smoking, CAD, BMI) as well as surgical characteristics (instrumentation, whether it was a revision, the number of levels treated) in predicting postoperative morbidity. These findings underscore the relative imprecision of traditional methods for risk

stratification in predicting postoperative morbidity. This suggests that morphometrics as a quantitative measure of sarcopenia and frailty may be more indicative of a patient’s general health and their physiological reserve for tolerating surgery. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. http://dx.doi.org/10.1016/j.spinee.2016.07.378

P54. Complications with Minimally Invasive Transforaminal Lumbar Interbody Fusion (MIS-TLIF) in the Morbidly Obese Population with Degenerative Spondylolisthesis Eiman Shafa, MD, James D. Schwender, MD; Twin Cities Spine Center, Minneapolis, MN, USA BACKGROUND CONTEXT: Treatment of the obese patient presents a unique operative and postoperative challenge for the surgeon. Some studies show an increased complication rate in obese patients following lumbar spine surgery. Controversy exists regarding complication rate and outcomes when comparing open and minimally invasive TLIF techniques in this population. PURPOSE: This study examines whether obesity is an independent risk factor for early perioperative complication resulting in poorer clinical outcomes in patients with degenerative spondylolisthesis treated by MIS-TLIF. STUDY DESIGN/SETTING: Retrospective cohort study. METHODS: Retrospective review of 134 consecutive patients with degenerative spondylolisthesis undergoing MIS-TLIF between 2010–2012. Patient demographics, perioperative variables and clinical outcome scores were collected over a minimum of 24 months. Intra-operative, in-hospital, and postoperative (<6 months) complications were assessed. Non-obese (N=65) and obese (N=69) cohorts were grouped by National Institutes of Health definitions and obese group further subdivided by Body Mass Index (I: 30–34, II: 35–39 III: 40 and over). Paired t-test and stepwise linear regression were used to determine the effect of obesity on clinical outcomes. RESULTS: There was no difference in intra-operative complications between the two groups (obese=2.9%, non-obese=4.6%; p=.362). Incidental durotomy was the only complication; none had sustained sequela. In-hospital complication rate was significantly greater in the obese group (obese=31.9%, nonobese=6.2%; p<.001). There was no difference in rate among obese subclasses. Genitourinary complications were most common (obese: 11.6%, nonobese 4.6%; p<.01). Pulmonary, cardiac and ileus complications were only experienced by obese patients (5.8%, 4.3%, 2.9% respectively). Sixmonth postoperative complication rate was statistically greater in the obese population (obese=13%, nonobese=7.6%; p<.01). Wound drainage was the most common complication (obese=4.3%, nonobese=0%). CONCLUSIONS: Obesity poses a unique challenge in treating patients with degenerative spondylolisthesis. In our experience, MIS-TLIF can be safely performed in the obese population despite a higher early postoperative complication rate. No permanent complications were experienced. Knowledge of common complications will help the treatment team appropriately manage obese patients with degenerative spondylolisthesis. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. http://dx.doi.org/10.1016/j.spinee.2016.07.379

P55. Nutritional Insufficiency as a Predictor for Adverse Outcomes in Anterior Cervical Discectomy and Fusion Parth Kothari, BS1, John Di Capua, MHS, BS2, Sulaiman Somani1, Joung Heon Kim, BS2, Dante M. Leven, DO, PT1, Jun Kim, MD3, Nathan J. Lee, BS1, Samuel K. Cho, MD2; 1Mount Sinai School of Medicine, New York, NY, USA; 2Icahn School of Medicine at Mount Sinai, New York, NY, USA; 3Mount Sinai Medical Center, New York, NY, USA BACKGROUND CONTEXT: Nutritional status is an important and significant factor in predicting adverse postoperative outcomes.

Refer to onsite annual meeting presentations and postmeeting proceedings for possible referenced figures and tables. Authors are responsible for accurately reporting disclosure and FDA device/drug status at time of abstract submission.