Faculty Bibliography

BACKGROUND CONTEXT/BACKGROUND:Lateral lumbar interbody fusion is a popular technique used in spine surgery. It is minimally invasive, provides indirect decompression, and allows for coronal plane deformity correction. Despite these benefits, the approach to lateral lumbar interbody fusion has been linked to complications associated with the lumbosacral plexus and vascular anatomy. As a result, vascular surgeons may be recruited for the exposure portion of the procedure. PURPOSE/OBJECTIVE:The purpose of this study was to compare exposure related complication and post-operative (postop) neuropraxia rates between exposure (EXP) and spine surgeon only (SSO) groups when performing the approach for lateral lumbar interbody fusion (LLIF). STUDY DESIGN/SETTING/METHODS:Retrospective analysis of patients treated at a single institution PATIENT SAMPLE: Patients undergoing LLIF procedures between 2012-2018 OUTCOME MEASURES: Operative time, estimated blood loss, fluoroscopy, length of stay, intra- and post-operative complications, and physiologic measures including pre- and post-operative motor examinations and unresolved neuropraxia METHODS: Patients who underwent LLIF were separated into EXP and SSO groups based on the presence or absence of vascular/general surgeon during the approach. The entire clinical history of patients with a decrease in pre and postop motor examination were reviewed for the presence of neuropraxia. All other intra- and postop exposure related complications were recorded for comparison. PSM was performed to account for age, Charlston Comorbity Index (CCI) % LLIFs including L4-L5, and number levels fused. Independent T-test and Chi-squared analyses were used to identify significant differences between EXP and SSO groups. Statistical significance was set at p<0.05. RESULTS:Two hundred seventy-five patients underwent LLIF procedures, 155 SSO and 120 EXP. Post-operatively, 26 patients (11.1%) experienced a drop in any MRC score, and two patients (0.7%) experience unresolved quadriceps palsies. The mean recovery time for MRC scores was 84.4 days. Other complications included 2 pneumothoraces (0.7%), 1 iliac vein injury (0.4%), 14 cases of ileus (5.1%), 3 pulmonary emboli (1.1%), 2 deep vein thrombosis (0.7%), 3 cases of abdominal wall paresis (1.1%), and one abdominal hematoma (0.4%). After PSM, demographics including age, gender, BMI, CCI, levels fused and operative time were similar between cohorts. Twenty patients had changes in pre- to postop motor scores (SSO 9.4%, EXP 12.4%, p>0.05). Iliopsoas motor scores decreased at the highest rate (EXP 12.4%, 8.2% SSO, p>0.05) followed by quadriceps (EXP 5.2%, SSO 4.7%, p>0.05). One SSO patient's postop course was complicated by a foot drop but returned to baseline within 1-year. One patient in EXP group developed an unresolved quadriceps palsy (EXP 1.0%, SSO 0.0% p>0.05). Intra-op exposure complications included one pneumothorax (EXP 1.0%, SSO 0.0%, p>0.05). There were no differences in PE/DVT, Ileus, or LOS. In the EXP cohort, three patients experienced abdominal wall paresis (EXP 2.9%, SSO 0.00%, p=0.246). CONCLUSIONS:Comparing the LLIF exposures performed by EXP and SSO, we found no significant difference in the rates of complications. Additional research is needed to determine the etiology of the abdominal wall complications. In conclusion, neuropraxia- and approach-related complications are similarly low between exposure and spine surgeons.

BACKGROUND:Lumbar herniated nucleus pulposus (HNP) is a common spinal pathology often treated by microscopic lumbar discectomy (MLD), though prior reports have not demonstrated which preoperative MRI factors may contribute to significant clinical improvement after MLD. PURPOSE/OBJECTIVE:To analyze the MRI characteristics in patients with HNP that predict meaningful clinical improvement in Health Related Quality of Life scores (HRQoL) after MLD. STUDY DESIGN/SETTING/METHODS:Retrospective clinical and radiological study of patients undergoing MLD for HNP at a single institution over a two-year period. PATIENT SAMPLE/METHODS:88 patients receiving MLD treatment for HNP. OUTCOME MEASURES/METHODS:Cephalocaudal Canal Migration; Canal & HNP Anterior-Posterior (AP) Lengths and Ratio; Canal & HNP Axial Areas and Ratio; Hemi-Canal & Hemi-HNP Axial Areas and Ratio; Disc appearance (black, grey or mixed), Baseline (BL) and 3-Month (3M) postoperative Health Related Quality of Life Scores. METHODS:Patients > 18 years old who received MLD for HNP with BL and 3M HRQoL scores of PROMIS (Physical Function, Pain Interference, and Pain Intensity), ODI, VAS Back, and VAS Leg scores were included. HNP and spinal canal measurements of cephalocaudal migration, AP length, area, hemi-area, and disc appearance were performed using T2 axial and sagittal MRI. HNP measurements were divided by corresponding canal measurements to calculate AP, Area, and Hemi-Area ratios. Using known minimal clinically important differences (MCID) for each ΔHRQoL score, patients were separated into two groups based on whether they reached MCID (MCID+) or did not reach MCID (MCID-). The MCID for PROMIS Pain Intensity was calculated using a decision tree. A linear regression illustrated correlations between PROMIS vs ODI and VAS Back/Leg scores. Independent t-tests and chi [2] tests were utilized to investigate significant differences in HNP measurements between the MCID+ and MCID- groups. RESULTS:± 43.2, p<.04). MCID+ patients had a greater Hemi-Area Ratio than MCID- patients had in 4 out of 6 HRQoL score comparisons (51.8% ± 14.7 vs 43.9% ± 14.9, p<.05). CONCLUSIONS:Patients who met MCID after MLD had larger HNP areas and larger Hemi-HNP Areas than those who did not meet MCID. These patients were also 2.7x more likely to have a grey MRI signal than a mixed or black MRI signal. When accounting for HNP area relative to canal area, patients who met MCID had greater Hemi-HNP canal occupation than patients who did not meet MCID. The results of this study suggest that preoperative MRI parameters can be useful in predicting patient reported improvement after MLD.

STUDY DESIGN/METHODS:Single-center retrospective study. OBJECTIVE:Investigate how differing degrees of PI modulate the recruitment of pelvic tilt (PT) in response to similar amounts of sagittal malalignment as measured by T1-Pelvic Angle (TPA). SUMMARY OF BACKGROUND DATA/BACKGROUND:Past research has shown that some patients do not recruit PT in response to sagittal malalignment. Given the anatomic relationship between PI and PT, we sought to determine whether differing PI is associated with variable recruitment of PT. METHODS:Single-center retrospective study of 2077 patients undergoing full body radiographs and TPA>10°. Five groups of patients (Very Low, Low, Average, High, and Very High PI) were defined utilizing PI ranges on a gaussian distribution. Linear regression (LR) evaluated correlation of TPA to PT within each PI group. Multivariate LR evaluated whether correlation between TPA and PT differed between each PI group. RESULTS:Mean PT increased with increasing levels of PI (p < 0.05). Within the full cohort, PT correlated with TPA (r = 0.80, p < 0.001). Multivariate LR revealed significant differences between slopes and intercepts of the linear relationship between PT and TPA within the PI groups. Compared to patients with an average PI, patients with Very Low PI had 3.4° lower PT while holding TPA constant (p < 0.001). Further, patients with Very High PI displayed a PT of 1.9° higher than patients with an Average PI while holding TPA constant (p = 0.01). A similar difference of -1.8°, and 1.2° with respect to the Average PI group was observed in the Low and High PI groups, respectively (p < 0.001). Means and standard deviations of PT at varying levels of TPA were defined for PI groups. CONCLUSIONS:This is the first study which demonstrated that PI is associated with varied recruitment of PT while maintaining constant sagittal malalignment. The results reported herein are intended to allow surgeons to assess a patient's magnitude of compensatory PT for an individual patient's PI. LEVEL OF EVIDENCE/METHODS:3.

STUDY DESIGN/METHODS:Retrospective review of a prospectively-collected database. OBJECTIVE:To define a simplified singular measure of cervical deformity (CD), C2 slope (C2S), which correlates with post-operative outcomes. SUMMARY OF BACKGROUND DATA/BACKGROUND:Sagittal malalignment of the cervical spine, defined by the cervical sagittal vertical axis (cSVA), has been associated with poor outcomes following surgical correction of the deformity. There has been a proliferation of parameters to describe cervical deformity (CD). This added complexity can lead to confusion in classifying, treating and assessing outcomes of CD surgery. METHODS:A prospective database of CD patients was analyzed. Inclusion criteria were cervical kyphosis>10°, cervical scoliosis>10°, cSVA>4 cm, or chin-brow vertical angle (CBVA) >25°. Patients were categorized into two groups and compared based on whether the apex of the deformity was in the cervical (C) or the cervicothoracic (CT) region. Radiographic parameters were correlated to C2S, T1-slope (T1S) and 1-year health-related quality-of-life (HRQL) outcomes as measured by the EuroQol 5 Dimension questionnaire (EQ5D), modified Japanese Orthopedic Association Scale (mJOA), numeric rating scale for neck pain (NRS neck), and the Neck Disability Index (NDI). RESULTS:104 CD patients (C = 74, CT = 30; mean age 61y, 56% women, 42% revisions) were included. CT patients had higher baseline cSVA and T1S (p < 0.05). C2S correlated with T1 slope minus cervical lordosis (TS-CL) (r = 0.98, p < 0.001) and C0-C2 angle, cSVA, CL, T1S (r = 0.37-0.65, p < .001). Correlation of cSVA with C0-C2 was weaker (r = 0.48, p < .001). At 1-year postoperatively, higher C2S correlated with worse EQ-5D (r = 0.28, p = .02); in CT patients, higher C2S correlated with worse NDI, mJOA, NRS neck and EQ5D (all r > 0.5, p≤.05). Using linear regression, moderate disability by EQ5D corresponded to C2S of 20°(r = 0.08). For CT patients, C2S = 17° corresponded to moderate disability by NDI (r = 0.4), and C2S = 20° by EQ5D (r = 0.25). CONCLUSION/CONCLUSIONS:C2S correlated with upper-cervical and subaxial alignment. C2S correlated strongly with TS-CL (R = .98, p < .001) because C2S is a mathematical approximation of TS-CL. C2S is a useful marker of CD, linking the occipitocervical and cervico-thoracic spine. C2S defines the presence of a mismatch between cervical lordosis and thoracolumbar alignment. Worse 1-year postoperative C2 slope correlated with worse health outcomes. LEVEL OF EVIDENCE/METHODS:3.

STUDY DESIGN/METHODS:Retrospective analysis OBJECTIVE.: Determine whether deformity corrections should vary by pelvic incidence (PI). SUMMARY OF BACKGROUND DATA/BACKGROUND:Alignment targets for deformity correction have been reported for various radiographic parameters. The T1 pelvic-angle (TPA) has gained in applications for ASD surgical-planning since it directly measures spinal alignment separate from pelvic- and lower-extremity compensation. Recent studies have demonstrated that ASD corrections should be age specific. METHODS:A prospective database of consecutive ASD patients was analyzed in conjunction with a normative spine database. Clinical measures of disability included the Oswestry Disability Index (ODI) and SF-36 Physical Component Score (PCS). Baseline relationships between TPA, age, PI and ODI/SF-36 PCS scores were analyzed in the ASD and asymptomatic patients. Linear regression modeling was used to determine alignment targets based on PI and age-specific normative SF-36-PCS values. RESULTS:903 ASD patients (mean 53.7y) and 111 normative subjects (mean 50.7y) were included. Patients were subanalyzed by PI: low, medium, high (<40, 40-75, >75); and age: elderly(>65y, n = 375) middle age(45-65y, n = 387) and young(18-45y, n = 141). TPA and SRS-Schwab parameters correlated with age and PI in ASD and normative subjects (r = .42, p < .0001). ODI correlated with PCS(r = .71, p < .0001). Linear regression analysis using age-normative SF-36-PCS values demonstrated that ideal spinopelvic alignment is less strict with increasing PI and age. CONCLUSIONS:Targets for ASD correction should vary by age and PI. This is demonstrated in both asymptomatic and ASD subjects. Using age-normative SF-36 PCS values, alignment targets are described for different age and PI categories. High-PI patients do not require as rigorous realignments to attain age-specific normative levels of health status. As such, sagittal spinal alignment targets increase with increasing age as well as PI. LEVEL OF EVIDENCE/METHODS:3.

STUDY DESIGN/METHODS:Retrospective review. OBJECTIVE:The aim of this study was to develop a novel surgical invasiveness index for cervical deformity (CD) surgery that incorporates CD-specific parameters. SUMMARY OF BACKGROUND DATA/BACKGROUND:There has been a surgical invasiveness index for general spine surgery and adult spinal deformity, but a CD index has not been developed. METHODS:CD was defined as at least one of the following: C2-C7 Cobb > 10°, cervical lordosis (CL) > 10°, cervical sagittal vertical axis (cSVA) > 4 cm, chin brow vertical angle (CBVA) > 25°. Consensus from experienced spine and neurosurgeons selected weightings for each variable that went into the invasiveness index. Binary logistic regression predicted high operative time (>338 minutes), estimated blood loss (EBL) (>600 cc), or length of stay (LOS; > 5 days) based on the median values of operative time, EBL and LOS. Multivariable regression modeling was utilized to construct a final model incorporating the strongest combination of factors to predict operative time, LOS, and EBL. RESULTS:85 CD patients were included (61yrs, 66%F). The variables in the newly developed CD invasiveness index with their corresponding weightings were: history of prior cervical surgery (3), anterior cervical discectomy and fusion (ACDF) (2/level), corpectomy (4/level), levels fused (1/level), implants (1/level), posterior decompression (2/level), Smith-Peterson osteotomy (2/level), three column osteotomy (8/level), fusion to upper cervical spine (2), absolute change in T1 slope minus cervical lordosis (TS-CL), cSVA, T4-T12 thoracic kyphosis and sagittal vertical axis (SVA) from baseline to 1-year. The newly developed CD-specific invasiveness index strongly predicted long LOS (R = 0.310, p < 0.001), high EBL (R = 0.170, p = 0.011), and extended operative time (R = 0.207, p = 0.031). A second analysis used multivariable regression modeling to determine which combination of factors in the newly developed index were the strongest determinants of operative time, LOS, and EBL. The final predictive model included: number of corpectomies, levels fused, decompression, combined approach, and absolute changes in SVA, cSVA and TK. This model predicted EBL (R = 0.26), operative time (R = 0.12), and LOS (R = 0.13). CONCLUSIONS:Extended length of stay, operative time, and high blood loss were strongly predicted by the newly developed CD invasiveness index, incorporating surgical factors and radiographic parameters clinically relevant for patients undergoing cervical deformity corrective surgery. LEVELS OF EVIDENCE/METHODS:4.

Cervical alignment has become increasingly important in the planning of spine surgery. A relationship between the slope of T1 (T1S), the cervical lordosis (CL), and the overall cervical sagittal vertical axis (cSVA) has previously been demonstrated, but the exact nature of this relationship is poorly understood. In this study, we derive theoretical and empirical equations to better understand how T1S and CL affect cSVA. The first equation was developed on a theoretical basis using inherent trigonometric relationships of the cervical spine. By treating the cervical spine as the arc of a circumference, and by taking into account the cervical height (CH), the geometric relationship between theT1S, CL, and cSVA was described via a trigonometric identity utilizing a novel angle δ subtended by the CH and cSVA (δ = T1S-CL/2). The second equation was developed on an empiric basis by performing a multiple linear regression on data obtained from a retrospective review of a large multicenter deformity database. The theoretical equation determined that the value of cSVA could be expressed as: $cSVA\ = \ CH*{\rm{tan}}( {\pi /180*( {T1S - CL/2} )} )$. The empirical equation determined that value of cSVA could be expressed as: $cSVA=({1.1*T1} )\ - ( {0.43*CL} ) + 6.69$. In both, the sagittal alignment of the head over the shoulders is directly proportional to the T1S and inversely proportional to CL/2. These 2 equations may allow surgeons to better understand how the CL compensates for the T1S, to accurately predict the postoperative cSVA, and to customize cervical interbody grafts by taking into consideration each individual patient's specific cervical spine parameters.

STUDY DESIGN:Retrospective review from a single institution. OBJECTIVE:To investigate the effect of hip osteoarthritis (OA) on spinopelvic compensatory mechanisms as a result of reduced hip range of motion (ROM) between sitting and standing. SUMMARY OF BACKGROUND DATA:Hip OA results in reduced hip ROM and contracture, causing pain during postural changes. Hip flexion contracture is known to reduce the ability to compensate for spinal deformity while standing; however, the effects of postural spinal alignment change between sitting and standing is not well understood. METHODS:Sit-stand radiographs of patients without prior spinal fusion or hip prosthesis were evaluated. Hip OA was graded by Kellgren-Lawrence grades and divided into low-grade (LOA; grade 0-2) and severe (SOA; grade 3 or 4) groups. Radiographic parameters evaluated were pelvic incidence (PI), pelvic tilt (PT), lumbar lordosis (LL), PI-LL, thoracic kyphosis (TK), SVA, T1-pelvic angle (TPA), T10-L2, proximal femoral shaft angle (PFSA), and hip flexion (PT change-PFSA change). Changes in sit-stand parameters were compared between LOA and SOA groups. RESULTS:548 patients were included (LOA = 311; SOA = 237). After propensity score matching for age, body mass index, and PI, 183 LOA and 183 SOA patients were analyzed. Standing analysis demonstrated that SOA had higher SVA (31.1 vs. 21.7), lower TK (-36.2 vs. -41.1), and larger PFSA (9.1 vs. 7.4) (all p < .05). Sitting analysis demonstrated that SOA had higher PT (29.7 vs. 23.3), higher PI-LL (21.6 vs. 12.4), less LL (31.7 vs. 41.6), less TK (-33.2 vs. -38.6), and greater TPA (27.9 vs. 22.5) (all p < .05). SOA had less hip ROM from standing to sitting versus LOA (71.5 vs. 81.6) (p < .05). Therefore, SOA had more change in PT (15.2 vs. 7.3), PI-LL (20.6 vs. 13.7), LL (-21.4 vs. -13.1), and T10-L2 (-4.9 vs. -1.1) (all p < .001), allowing the femurs to change position despite reduced hip ROM. SOA had greater TPA reduction (15.1 vs. 9.6) and less PFSA change (86.7 vs. 88.8) compared with LOA (both p < .001). CONCLUSIONS:Spinopelvic compensatory mechanisms are adapted for reduced hip joint motion associated with hip OA in standing and sitting. LEVEL OF EVIDENCE:Level III.

OBJECTIVE:Obesity, a condition that is increasing in prevalence in the United States, has previously been associated with poorer outcomes following deformity surgery, including higher rates of perioperative complications such as deep and superficial infections. To date, however, no study has examined the relationship between preoperative BMI and outcomes of deformity surgery as measured by spine parameters such as the sagittal vertical axis (SVA), as well as health-related quality of life (HRQoL) measures such as the Oswestry Disability Index (ODI) and Scoliosis Research Society-22 patient questionnaire (SRS-22). To this end, the authors sought to clarify the relationship between BMI and postoperative change in SVA as well as HRQoL outcomes. METHODS:The authors performed a retrospective review of a prospectively managed multicenter adult spinal deformity database collected and maintained by the International Spine Study Group (ISSG) between 2009 and 2014. The primary independent variable considered was preoperative BMI. The primary outcome was the change in SVA at 1 year after deformity surgery. Postoperative ODI and SRS-22 outcome measures were evaluated as secondary outcomes. Generalized linear models were used to model the primary and secondary outcomes at 1 year as a function of BMI at baseline, while adjusting for potential measured confounders. RESULTS:Increasing BMI (compared to BMI < 18) was not associated with change of SVA at 1 year postsurgery. However, BMIs in the obese range of 30 to 34.9 kg/m2, compared to BMI < 18 at baseline, were associated with poorer outcomes as measured by the SRS-22 score (estimated change -0.47, 95% CI -0.93 to -0.01, p = 0.04). While BMIs > 30 appeared to be associated with poorer outcomes as determined by the ODI, this correlation did not reach statistical significance. CONCLUSIONS:Baseline BMI did not affect the achievable SVA at 1 year postsurgery. Further studies should evaluate whether even in the absence of a change in SVA, baseline BMIs in the obese range are associated with worsened HRQoL outcomes after spinal surgery.