Jonathan H. Oren

Medical Complications After Adult Spinal Deformity Surgery: Incidence, Risk Factors, and Clinical Impact.

Study Design. Retrospective review of a prospective multicenter database evaluating surgical adult spinal deformity (ASD) patients. Objective. This study aims to identify risk factors for medical complications in ASD patients undergoing surgery. Summary of Background Data. ASD surgery is known for its high complication rate. This study examines baseline patient characteristics for predictors of medical complications in surgical ASD patients. Methods. Intra and perioperative medical complications were included. Medical complications were: infection, pneumonia, urinary tract infection, c-difficile, sepsis, stroke, delirium, deep venous thrombosis, pulmonary embolism, myocardial infarction, arrhythmia, congestive heart failure, pneumothorax, atelectasis, adult respiratory distress syndrome, bowel obstruction, ileus, and renal failure. Potential predictors were identified using univariate testing. Multivariate Poisson regression was used to determine independent predictors of medical complications. Health-related quality of life (HRQL) was measured using the Oswestry Disability Index and SF-36. Multivariate repeated measures mixed models were used to examine HRQL. Results. Four hundred forty-eight patients were included. The incidence of patients with at least one medical complication was 26.8%. Potential predictors included: age, BMI, anemia, arthritis, depression, cardiac history, hypertension, lung disease, history of PVD, Charlson Comorbidity Index, ASA, smoking, sex, and the number of years with spine problems. Independent predictors identified on multivariate logistic regression modeling included hypertension (IRR 2.43 P = 0.0001), smoking (IRR 2.49 P = 0.0001), and number of years with spine problems (IRR 1.23 P = 0.03). Despite medical complications, patients experienced significant improvements in HRQL, as measured by the SF-36 (P = 0.0001) and oswestry disability index (P = 0.0001). The rate of improvement and overall improvement compared with baseline were not statistically different than that of patients who did not experience medical complications. Conclusion. Risk factors for the development of postoperative medical complications after correction of ASD include smoking, hypertension, and duration of symptoms. Patients who have one or more of these risk factors should be identified and informed during informed consent of their increased risks. They should be optimized preoperatively, and followed closely during the postoperative period. Level of Evidence: 3

Predicting Cervical Alignment Required to Maintain Horizontal Gaze Based on Global Spinal Alignment.

Study Design. A retrospective cohort. Objective. The aim of this study was to investigate the cervical alignment necessary for the maintenance of horizontal gaze that depends on underlying thoracolumbar alignment. Summary of Background Data. Cervical Sagittal Curve (CC) is affected by thoracic and global alignment. Recent studies suggest large variability in normative CC ranging from lordotic to kyphotic alignment. No previous studies have assessed the effect of global spinal alignment on CC in maintenance of horizontal gaze. Methods. Patients without previous history of spinal surgery and able to maintain their horizontal gaze while undergoing full body imaging were included. Patients were stratified on the basis of thoracic kyphosis (TK) into (<30, 30–40, 40–50, and >50) and then by SRS-Schwab sagittal vertical axis (SVA) modifier into (posterior alignment SVA <0, aligned 0–50, and malaligned >50 mm). Cervical alignment was assessed among SVA grade in TK groups. Stepwise linear regression analysis was applied on random selection of 60% of the population. A simplified formula was developed and validated on the remaining 40%. Results. In each TK group (n = 118, 137, 125, 197), lower CC (C2-C7) was significantly more lordotic by increased Schwab SVA grade. T1 slope and cervical SVA significantly increased with increased thoracolumbar (C7-S1) SVA. Upper CC (C0-C2) and mismatch between T1 slope and CC (T1-CL) were similar. Regression analysis revealed LL minus TK (LL-TK) as an independent predictor (r = 0.640, r2 = 0.410) with formula: CC = 10- (LL-TK)/2. Validation revealed that the absolute difference between the predicted CC and the actual CC was 8.5°. Moreover, 64.2% of patients had their predicted C2-C7 values within 10° of the actual CC. Conclusion. Cervical kyphosis may represent normal alignment in a significant number of patients. However, in patients with SVA >50 and greater thoracic kyphosis, cervical lordosis is needed to maintain the gaze. Cervical alignment can be predicted from underlying TK and lumbar lordosis, which may be clinically relevant when considering correction for thoracolumbar or cervical deformity Level of Evidence: 3

Global sagittal axis: a step toward full-body assessment of sagittal plane deformity in the human body.

OBJECTIVE Sagittal malalignment requires higher energy expenditure to maintain an erect posture. Because the clinical impact of sagittal alignment is affected by both the severity of the deformity and recruitment of compensatory mechanisms, it is important to investigate new parameters that reflect both disability level and compensatory mechanisms for all patients. This study investigated the clinical relevance of the global sagittal axis (GSA), a novel measure to evaluate the standing axis of the human body. METHODS This is a retrospective review of patients who underwent full-body radiographs and completed health-related quality of life (HRQOL) questionnaires: Oswestry Disability Index (ODI), Scoliosis Research Society-22, EuroQol-5D (EQ-5D), and the visual analog scale for back and leg pain. The GSA was defined as the angle formed by a line from the midpoint of the femoral condyles to the center of C-7, and a line from the midpoint between the femoral condyles to the posterior superior corner of the S-1 sacral endplate. After evaluating the correlation of GSA/HRQOL with sagittal parameters, linear regression models were generated to investigate how ODI and GSA related to radiographic parameters (T-1 pelvic angle, pelvic retroversion, knee flexion, and pelvic posterior translation). RESULTS One hundred forty-three patients (mean age 44 years) were included. The GSA correlated significantly with all HRQOL (up to r = 0.6 with EQ-5D) and radiographic parameters (up to r = 0.962 with sagittal vertical axis). Regression between ODI and sagittal radiographic parameters identified the GSA as an independent predictor (r = 0.517, r2 = 0.267; p < 0.001). Analysis of standardized coefficients revealed that when controlling for deformity, the GSA increased with a concurrent decrease in pelvic retroversion (-0.837) and increases in knee flexion (+0.287) and pelvic posterior translation (+0.193). CONCLUSIONS The GSA is a simple, novel measure to assess the standing axis of the human body in the sagittal plane. The GSA correlated highly with spinopelvic and lower-extremities sagittal parameters and exhibited remarkable correlations with HRQOL, which exceeded other commonly used parameters.

Effect of antifibrinolytic therapy on complications, thromboembolic events, blood product utilization, and fusion in adult spinal deformity surgery

Study Design. A multicenter, prospective, consecutive database of surgical patients with adult spinal deformity (ASD). Objective. This study investigated the use of antifibrinolytic (AF) therapy in ASD surgery. Summary of Background Data. AF therapy has been shown to be effective in preventing blood loss in some settings. Its effect on major and minor perioperative complications, blood product utilization, vascular events, and postoperative fusion in patients undergoing ASD surgery remains unclear. Methods. All patients with data on AF use were included. Parameters of blood utilization included transfusion rates and units of packed red blood cells and fresh frozen plasma transfused. Thromboembolic events included stroke, deep vein thrombosis, and pulmonary embolus. Multivariate regression was used, accounting for confounders. Results. Four hundred three patients were included. One hundred thirty-seven patients received aminocaproic acid (EACA), 81 received tranexamic acid (TXA), and 185 received no AFs. The use of AF was associated with a decrease in transfusion (EACA: odds ratio [OR] = 0.38, P = 0.043; TXA: OR = 0.31, P = 0.047), a decrease in the number of units of packed red blood cells transfused (EACA: incidence risk ratio [IRR] = 0.45, P = 0.0005; TXA: IRR = 0.7, P = 0.0005), and a decrease in the number of fresh frozen plasma transfused (EACA: IRR = 0.65, P = 0.003; TXA: IRR = 0.67, P = 0.006). AF use was associated with an increase in minor intraoperative complications (EACA: IRR = 2.15, P = 0.008; TXA: IRR = 2.12, P = 0.011). TXA use (but not EACA) was associated with a decrease in the incidence of major perioperative complications compared with no AF (IRR = 0.37, P = 0.019). There was no difference in the incidence of thromboembolic events. Conclusion. TXA or EACA use was associated with increased minor intraoperative complications. TXA was associated with decreased major perioperative complications. AF was associated with decreased utilization of blood products without an increased rate of thromboembolic events. Given the nature of this study, transfusion threshold was not standardized. Future studies with rigid criteria for transfusion should be prospectively performed to better evaluate the impact of AF during ASD surgery. Level of Evidence: 3

Developing the Total Disability Index Based on an Analysis of the Interrelationships and Limitations of Oswestry and Neck Disability Index.

Study Design. Retrospective. Objective. This study assessed the feasibility of combining Oswestry and Neck Disability Index (ODI and NDI) into 1 shorter “Total Disability Index” (TDI) from which reconstructed scores could be computed. Summary of Background Data. ODI and NDI are not pure assessments of disability related to back and neck, respectively. Because of similarities/redundancies of questions, ODI scores may be elevated in neck-pain patients and the converse is true for NDI in back-pain patients. Methods. Spine patients completed ODI and NDI, and complaints were recorded as back pain (BP), neck pain (NP), or both (BNP). Questionnaire scores were compared across cohorts via descriptives and Spearman (&rgr;) correlations. In exploring the feasibility of merging ODI/NDI, TDI was constructed from 9 ODI and 5 NDI items. Extracting questions from TDI, reconstructed 9-item rODI and 10-item rNDI indices were formed and compared with true ODI/NDI. Results. There were a total of 1207 patients: 741 BP, 134 NP, and 268 BNP. Mean ODI was 37 ± 21 and mean NDI was 32 ± 21. Patients with concurrent BP and NP had significantly more disability. Seventy-eight patients of 134 (58%) patients with NP only had at least “moderate disability” by ODI and 297 of 741 (40%) patients with back pain only, had at least “moderate disability” by NDI. ODI versus NDI correlation was &rgr; = 0.755; ODI versus reconstructed rODI correlated at &rgr; = 0.985, and NDI versus reconstructed rNDI correlated at &rgr; = 0.967 (P < 0.01). Conclusion. Elevated ODI/NDI scores in patients with isolated complaints show that disability in 1 region affects scores on both surveys. This study constructed a 14-item TDI that represents every domain of ODI/NDI with exception of ODI “Sex Life.” From this TDI, reconstructed scores correlated near perfectly with true scores. TDI provides a more global assessment of spinal disability and is a questionnaire that reduces the time burden to patients. The TDI allows for simultaneous assessment of back, neck, and global spinal disability. Level of Evidence: 2

Is There a Gender-Specific Full Body Sagittal Profile for Different Spinopelvic Relationships? A Study on Propensity-Matched Cohorts

DESIGN Retrospective review. OBJECTIVE To evaluate gender-related differences in compensatory recruitment to progressive sagittal malalignment. Recent research has elucidated compensatory mechanisms recruited in response to sagittal malalignment, but gender-specific differences in compensatory recruitment patterns is unknown. METHODS Single-center study of patients with full body x-rays. A female group was propensity matched by age, body mass index (BMI), and pelvic incidence (PI) to a male group. Patients were then stratified into five groups of progressive PI-lumbar lordosis (LL) mismatch (<0°, 0°-10°, 10°-20°, 20°-30°, >30°). Differences between PI-LL groups were assessed with analysis of variance, and between genders by unpaired t test. Knee flexion to pelvic tilt (PT) ratio was computed and compared between genders. Multivariate regression to develop predictive models for PT was performed for each gender, first with spinopelvic parameters and subsequently with inclusion of lower limb parameters. RESULTS A total of 942 patient visits were included: 471 females (mean age 54 years, BMI 27, PI 51°) and 471 males (mean age 52 years, BMI 27, PI 51°). At the lowest level of malalignment, females had greater PT and less knee flexion. With progressive malalignment, females continued to exhibit a pattern of greater pelvic retroversion and less knee flexion compared to males. Hip extension was higher in females with progressive PI-LL mismatch groups. Both genders progressively recruited knee flexion and pelvic retroversion with increased PI-LL mismatch, except that at the higher PI-LL mismatch groups, only males continued to recruit knee flexion (all p < .05). Inclusion of lower limbs in the regression for PT markedly improved correlation coefficients for females but not for males. CONCLUSIONS With progressive sagittal malalignment, men recruit more knee flexion and women recruit more pelvic tilt and hip extension. Knee flexion is a possible mechanism to gain pelvic tilt for females whereas for males, knee flexion is an independent compensatory mechanism.DESIGN Retrospective review. OBJECTIVE To evaluate gender-related differences in compensatory recruitment to progressive sagittal malalignment. SUMMARY OF BACKGROUND DATA Recent research has elucidated compensatory mechanisms recruited in response to sagittal malalignment, but gender-specific differences in compensatory recruitment patterns is unknown. METHODS Single-center study of patients with full body x-rays. A female group was propensity matched by age, body mass index (BMI), and pelvic incidence (PI) to a male group. Patients were then stratified into five groups of progressive PI-lumbar lordosis (LL) mismatch (<0°, 0°-10°, 10°-20°, 20°-30°, >30°). Differences between PI-LL groups were assessed with analysis of variance, and between genders by unpaired t test. Knee flexion to pelvic tilt (PT) ratio was computed and compared between genders. Multivariate regression to develop predictive models for PT was performed for each gender, first with spinopelvic parameters and subsequently with inclusion of lower limb parameters. RESULTS A total of 942 patient visits were included: 471 females (mean age 54 years, BMI 27, PI 51°) and 471 males (mean age 52 years, BMI 27, PI 51°). At the lowest level of malalignment, females had greater PT and less knee flexion. With progressive malalignment, females continued to exhibit a pattern of greater pelvic retroversion and less knee flexion compared to males. Hip extension was higher in females with progressive PI-LL mismatch groups. Both genders progressively recruited knee flexion and pelvic retroversion with increased PI-LL mismatch, except that at the higher PI-LL mismatch groups, only males continued to recruit knee flexion (all p < .05). Inclusion of lower limbs in the regression for PT markedly improved correlation coefficients for females but not for males. CONCLUSIONS With progressive sagittal malalignment, men recruit more knee flexion and women recruit more pelvic tilt and hip extension. Knee flexion is a possible mechanism to gain pelvic tilt for females whereas for males, knee flexion is an independent compensatory mechanism.

Variability Over Time of Preoperative Sagittal Alignment Parameters: Radiographic and Clinical Considerations.

Study Design. Retrospective review. Objective. To evaluate preoperative variability in radiographic sagittal parameters in adult spinal deformity (ASD). Summary of Background Data. In ASD surgical planning, deformity magnitude is determined from preoperative radiographs. There are no studies evaluating the clinical relevance and timing to repeat radiographs during interval clinic visits and timing to repeat radiograph for preoperative planning. Methods. A total of 139 patients with ASD with minimum two preoperative full-body spine x-rays were included. Cervical, thoracic, lumbar, pelvic, and hip/knee sagittal alignment parameters were analyzed using dedicated spine measurement software. Patients were grouped by time intervals between x-rays: A: 8 weeks or lesser, B: 10 to 20 weeks, and C: 21 weeks or more. Changes in sagittal parameters were correlated to age and deformity magnitude (T1 pelvic angle or pelvic tilt [PT] >20°). Results. The cohort had mean age 59 years, mean body mass index 27, 30% men, 95 patients with no prior spine surgery, and 44 patients at minimum 9 months since prior spine surgery. There were 25 patients in group A, 38 in B, and 71 in C. All radiographic measures showed good time-based consistency at intervals less than 21 weeks (groups A and B). Group C had significant increases in PT (1.5°) and hip extension (2.1°) (P < 0.05). These changes were greater in group C patients with previous surgery (PT 3.7°; P < 0.006, hip extension 3.2°; P < 0.025). Greater interval changes in parameters were also associated with higher magnitudes of deformity and younger patient ages. Conclusion. All sagittal radiographic parameters were statistically consistent at intervals of less than 21 weeks. In patients with more than 21 weeks between interval x-rays, change in PT was greater than the standard error of measurement for patients with prior surgery or severe deformity. Consideration should be made to obtain new x-rays for patients with ASD when the interval between clinical visits exceeds 5 months. Level of Evidence: 4

Body mass index predicts risk of complications in lumbar spine surgery based on surgical invasiveness

BACKGROUND CONTEXT Obesity as a comorbidity in spine pathology may increase the risk of complications following surgical treatment. The body mass index (BMI) threshold at which obesity becomes clinically relevant, and the exact nature of that effect, remains poorly understood. PURPOSE Identify the BMI that independently predicts risk of postoperative complications following lumbar spine surgery. STUDY DESIGN/SETTING Retrospective review of the National Surgery Quality Improvement Program (NSQIP) years 2011-2013. PATIENT SAMPLE A total of 31,763 patients were undergoing arthrodesis, discectomy, laminectomy, laminoplasty, corpectomy, or osteotomy of the lumbar spine. OUTCOME MEASURES Complication rates. METHODS The patient sample was categorized preoperatively by BMI according to the World Health Organization stratification: underweight (BMI <18.5), normal overweight (BMI 20.0-29.9), obesity class 1 (BMI 30.0-34.9), 2 (BMI 35.0-39.9), and 3 (BMI≥40). Patients were dichotomized based on their position above or below the 75th surgical invasiveness index (SII) percentile cutoff into low-SII and high-SII. Differences in complication rates in BMI groups were analyzed by Bonferroni analysis of variance (ANOVA) method. Multivariate binary logistic regression evaluated relationship between BMI and complication categories in all patients and in high-SII and low-SII surgeries. RESULTS Controlling for baseline difference in SII, Charlson Comorbidity Index (CCI) score, diabetes, hypertension, and smoking, complications significantly increased at a BMI of 35 kg/m2. The odds ratios for any complication (odds ratio [OR] [95% confidence interval {CI}]; obesity 2: 1.218 [1.020-1.455]; obesity 3: 1.742 [1.439-2.110]), infection (obesity 2: 1.335 [1.110-1.605]; obesity 3: 1.685 [1.372-2.069]), and surgical complication (obesity 2: 1.622 [1.250-2.104]; obesity 3: 2.798 [2.154-3.634]) were significantly higher in obesity classes 2 and 3 relative to the normal-overweight cohort (all p<.05). CONCLUSION There is a significant increase in complications, specifically infection and surgical complications, in patients with BMI≥35 following lumbar spine surgery, with that rate further increasing with BMI≥40.

Defining the Role of the Lower Limbs in Compensating for Sagittal Malalignment

Study Design. Retrospective review. Objective. To investigate the role of lower limbs compensation with progressive sagittal malalignment. Summary of Background Data. Although lower limb compensatory mechanisms are established response to progressive sagittal malalignment, their specific role and potential impact on surgical planning has not been evaluated. Methods. Single center retrospective review of full body x-rays was performed in patients of age >20 years. Parameters were measured with dedicated software. Population was stratified by 50 mm intervals of sagittal vertical axis (SVA) and one-way ANOVA was performed to compare P.shift (P.shift = anteroposterior translation of the pelvis vs. the feet) across SVA groups. Anteroposterior offset of each vertebra in relation to a vertical line extended from the distal tibial metaphysis (TM) was investigated. Linear regression was performed to predict pelvic tilt (PT) using Knee angle (KA) and P.shift, whereas controlling for pelvic incidence minus lumbar lordosis mismatch (PI-LL) and SVA. Results. A total of 2124 patient visits were included (PI = 55.1 ± 14.1°, PT=21.0 ± 11°, PI-LL=6.3 ± 17.3°, SVA = 29 ± 51 mm). With progressively increased SVA, P.shift decreased from 30 to −100 mm (all P < 0.005). Analysis of vertebral offset from the distal tibial metaphysis revealed that T9 was aligned with the TM line across all SVA groups. Prediction of PT based on PI-LL and SVA yielded R2=0.76 (P < 0.001). Subsequent addition of KA and P.shift as independent parameters using hierarchical multiple regression led to significant improvement in R2, demonstrating the independent role of lower limbs parameters in PT prediction. KA and P.shift had a positive standardized coefficient (all P < 0.05). Conclusion. Lower limb compensatory mechanisms increase with progressive sagittal malalignment. Anteroposterior translation of pelvis allows the T9 vertebra to remain in line with the ankle (“conus of economy”). Lower limb compensatory mechanisms are positive predictors of PT and thus do not require additional consideration in surgical realignment planning. Level of Evidence: 3