The same patient cohort and similar methodologies were utilized from our previous publication by Hirase et al.14 The local institutional review board approved the study procedure on April 13, 2020. Due to the retrospective observational nature of this study, the informed consent was waived.
Study Population
Between May 2016 and February 2020, a retrospective analysis was performed at a single institution of patients receiving complex revision thoracolumbar spine surgery by three board certified fellowship-trained orthopaedic spine surgeons. The same inclusion and exclusion criteria for the same cohort of patients from our previous publication by Hirase et al. was applied for this study.14 Any patients age 18 or above undergoing complex revision thoracolumbar spine surgery were included. Any history of prior surgical intervention of the same vertebral level was defined as revision surgery. A Spine Surgical Invasiveness Index (SSII) > 10 was used to define complex surgery.18 Patients lacking a pre-operative CT or MRI of the lumbar spine obtained at our facility within six months of surgery, poor image quality, pre-operative MRI or CT acquired at any outside facilities, clinical evidence of L1 or L2 nerve root compression, a history of previous surgical treatment to or through the psoas muscle, and coronal deformity greater than 20 degrees were excluded as mentioned in our previous study.14
Data Collection
Electronic medical records were utilized retrospectively to obtain demographic data including age, gender, BMI, American Anesthesiologists’ Society (ASA) class, comorbidities, indication for revision operation, baseline ambulation status, and presence of neurologic deficits. BMI ≥ 30.0 kg/m2 was used to define obesity. Intraoperative data was acquired which included estimated blood loss (EBL) and operative time defined as time of incision to post-operative dressing placement. SSII, a verified method of evaluation and comparison regarding spine surgery complexity was used, with a range of 0–48, which accounts for surgical approaches and the amount of decompressed, fused, and instrumented vertebral levels. 18 In regard to the included surgical population with revision surgeries, only the additional levels of fusion, instrumentation, or decompression were accounted for the SSII calculation as previously stated.14 Each patients’ primary surgery SSII score was also obtained.
Assessment Of Sarcopenia
PMI was used to analyze sarcopenia, which was calculated by measuring the total cross-sectional area (CSA) of the bilateral psoas muscles at the L3 vertebral body using the pre-operative T1 weighted MRI or CT normalized to body height2 (mm2/m2). The total CSA was measured using OsiriX DICOM Viewer software (Version 11.0, Bernex, Switzerland) by manual outlining the bilateral psoas muscles at the first axial cut, done in the craniocaudal direction where both transverse processes are visible at the L3 level. 14,15 All of the images were obtained at a single institution with the same scanning protocols ensuring identical scanning thickness among all images analyzed. Three separate reviewers performed all measurements to improve interobserver reliability. Each measurement was acquired three times by all reviewers to improve intraobserver reliability. Intraclass correlation coefficient (ICC) was used to assess interobserver and intraobserver reliabilities, where an ICC above 0.90 signifies excellent agreement, between 0.75 and 0.90 signifies good agreement, between 0.5 and 0.75 signifies moderate agreement, and below 0.5 signifies poor agreement.16 Each of the mean values obtained by the three reviewers was divided by the square of patient height to calculate the PMI as previously described.14 To minimize the risk of bias, all reviewers were blinded to their respective measurements as well as to patient demographics and outcomes. Sarcopenia was defined as PMI < 500 mm2/m2 for males and < 412 mm2/m2 for females as previously defined.14
Outcome Measures
Retrospective analysis of electronic medical records were used to review all perioperative outcomes. The primary outcome measures were perioperative AEs which included post-operative anemia that required transfusion, cardiac complication (cardiac arrest and myocardial infarction), sepsis, wound complication (wound dehiscence and deep wound infection), acute kidney injury (AKI), delirium, intra-operative dural tear, pneumonia, urinary tract infection (UTI), urinary retention, epidural hematoma, and deep vein thrombosis (DVT). The secondary outcome measures used were 30-day readmission rates, 30-day re-operation rates, in-hospital mortality rates, discharge disposition (home vs facility) and post-operative hospital length of stay (LOS). The number of days from surgery (or the last surgery if staged procedure) to discharge to either home or facility was used to defined postoperative LOS.
Statistical Analysis
SPSS statistical software (Version 25.0; SPSS, Inc, Chicago, IL) was utilized to perform data analysis. The Chi-Square or Fisher’s exact test and continuous data was used to analyze categorical data and was further analyzed using Two-tailed student t-test. Continuous variables with non-normal distribution was analyzed using the Mann-Whitney U test. Statistical significance was set to p-value < 0.05. The odds ratio (OR) with 95% confidence interval (CI) was calculated for comparing perioperative outcomes. Post hoc power analysis with a two-tailed alpha of 0.05 was performed between obese and non-obese groups to evaluate the power of detecting differences between patients experiencing any perioperative. A multivariable logistic regression model was used to determine the effects of sarcopenia, obesity, age, and gender on the likelihood of the occurrence of any AE.