Faculty Bibliography

BACKGROUND CONTEXT: Surgery for degenerative spondylolisthesis (DS) is common with good clinical outcomes. Several high quality studies have examined outcomes following DS surgery, but few have identified risk factors for re-operation. PURPOSE: To investigate the incidence of re-operation and associated risk factors among the surgically treated patients from the DS arm of the Spine Patient Outcomes Research Trial (SPORT), randomized and observational cohorts. Our study hypothesis was that certain patient characteristics would emerge as risk factors for re-operation. STUDY DESIGN/SETTING: A retrospective subgroup analysis of the 8- year data from the SPORT trial. PATIENT SAMPLE: 406 patients who underwent surgery for DS. OUTCOME MEASURES: Incidence of re-operation, risk factors. METHODS: A retrospective subgroup analysis was performed on surgically treated patients enrolled in the DS arm of the multicenter SPORT trial, randomized and observational cohorts. Included patients had neurogenic claudication for at least 12 weeks, clinical neurological signs, spinal stenosis on cross-sectional imaging, and DS on standing lateral radiographs. In our subgroup analysis, patients were stratified into no re-operation versus re-operation. Baseline characteristics were analyzed using multivariate regression from data collected from patients at eight years postoperatively. A Cox regression model Stepwise Method was implemented in SAS with p=0.10 significant for entry and p=0.05 significant for retention with calculation of hazard ratios (HR). RESULTS: Of the 406 surgery patients, 73% underwent instrumented fusion, 21% non-instrumented fusion, and 6% decompression alone. At 8 years, the re-operation rate was 22%, 315 having no re-operation and 91 in the re-operation group. Twenty-five (28%) were within the first year, 49 (54%) within 2 years, 64 (70%) within 4 years, and 78 (86%) within 6 years. Forty-one revisions (10%) were for progressive DS, 33 (8%) for complication or other reason, and 13 (3%) for a new co!

BACKGROUND CONTEXT: Lumbar spinal stenosis (SpS) is a common degenerative disease involving narrowing of the spinal canal that may lead to pain and disability. Spinal stenosis is the most common indication for surgery in the elderly population and was the fastest growing spine surgery in the last three decades. Prospective studies have shown that timely surgical intervention can be effective in restoring function in these patients, with variable re-operation rates. Few long-term studies have identified consistent risk factors for re-operation following surgery for SpS. PURPOSE: To investigate the incidence of re-operation and associated risk factors among the surgically treated patients from the SpS arm of the Spine Patient Outcomes Research Trial (SPORT), randomized and observational cohorts. Our study hypothesis was that specific patient baseline characteristics would emerge as risk factors for re-operation in patients treated surgically for SpS. STUDY DESIGN/SETTING: A retrospective subgroup analysis of the eight-year data from the SPORT trial. PATIENT SAMPLE: 417 patients who underwent surgery for SpS. OUTCOME MEASURES: Incidence of re-operation, risk factors. METHODS: A retrospective subgroup analysis was performed on surgically treated patients enrolled in the SpS arm of the multicenter SPORT trial randomized and observational cohorts. Patients included in the SpS arm had neurogenic claudication for at least 12 weeks and spinal stenosis, without spondylolisthesis or instability, as confirmed on imaging. In our subanalysis, patients were stratified into no re-operation versus reoperation. Baseline characteristics were analyzed using a multivariate regression analysis based on data collected from patients at eight years postoperatively. A Cox regression model Stepwise Method was implemented in SAS with p=0.10 significant for entry and p=0.05 significant for retention to the model. RESULTS: Of the 417 surgery patients, 88% underwent decompression only, 6% noninstrumented fusion, and 6% instr!

BACKGROUND CONTEXT: Radiographic deterioration and persistent deformity is not an uncommon outcome after major sagittal spinal deformity surgery. The high rate of sagittal misalignment after surgery for patients with sagittal spinal deformity (SSD) has highlighted the need to develop better preoperative surgical planning, which can include Smith Peterson Osteomy (SPO), pedicle substraction osteotomy (PSO), transforaminal lumbar interbody fusion (TLIF), and selection of upper instrumented vertebrae (UIV). PURPOSE: This study evaluates preoperative planning and changes in procedure execution as a root cause analysis of radiographic outcomes. STUDY DESIGN/SETTING: Prospective, single-center study of consecutive SSD patients undergoing major sagittal realignment surgery. PATIENT SAMPLE: 40 adults treated surgically for spinopelvic misalignment (SVA>50mm, PT>20degree, or PI-LL>20degree). OUTCOME MEASURES: Thoracic Kyphosis (TK), Lumbar Lordosis (LL), Pelvic Incidence - Lumbar Lordosis (PI-LL). METHODS: Consecutive SSD patients who required osteotomies were included. Preoperative plans, and radiographs at baseline and 3 months were collected. Major changes in the surgeries were classified in 2 groups: less aggressive procedure (LAP, >1 SPO (Smith Peterson osteotomy) not done, PSO (pedicle subtraction osteotomy) replaced by SPO) and more aggressive procedure (MAP, add>1 SPO). Patients without major change were grouped as no major change (NMC). Preoperative, anticipated (by Surgimap planning software), and postoperative alignments were compared between LAP and NMC cohorts. RESULTS: There were 40 patients (mean 62 +12 years) with 25 NMC patients and 15 with major change (13 LAP and 2 MAP). Comparison of planned and postoperative alignments demonstrated that postoperative TK was greater than expected and LL was under corrected (NMC: 48% and LAP: 62%). The LAP cohort had greater mismatch between pelvic incidence and lumbar lordosis (PI-LL) at baseline (49+12 vs 29+17, p=0.001), was planned for greater cha!

BACKGROUND CONTEXT: Previous data have indicated that ASD can be a debilitating disease that impacts physical function to a similar degree as diabetes and heart disease. Correlation of specific deformity types to other disease states demonstrated that patients with severe sagittal malalignment reported similar disability as poorly functioning amputee patients. Little data exists comparing the impact of operative and nonoperative treatment on the disease state for ASD patients and correlating the change in physical function to comparable disease states. PURPOSE: Compare baseline and two year follow up SF-36v2 Health Survey (SF-36) scores of ASD patients treated operatively and nonoperatively to evaluate the ability of operative or nonoperative treatment to 1) restore ASD patients to normative physical function levels and 2) identify disease state correlates for different deformity types and the ability of treatment to improve health status. STUDY DESIGN/SETTING: Multicenter, prospective, consecutive case series. PATIENT SAMPLE: ASD patients (scoliosis >20degree, sagittal vertical axis (SVA) >5cm, pelvic tilt (PT) >25degree, and/or thoracic kyphosis (TK) >60degree), age>18 years. OUTCOME MEASURES: Short Form 36 Health Survey Standard Form Version 2 (SF-36). METHODS: Prospective analysis of consecutive ASD patients enrolled into a multicenter database. Inclusion criteria: no prior spine surgery, age>18years, ASD, and minimum 2-year follow-up. ASD evaluated according to: (1) type of scoliosis (thoracic, lumbar, thoracic and lumbar or none) and (2) severity of sagittal malalignment (sagittal vertical axis [SVA]). Patients divided into those treated operatively (OP) or nonoperatively (NON). Baseline and 2-year follow up SF-36 physical component (PCS) and mental component (MCS) scores calculated for each group and compared to US normative and disease-specific values. SF-36 reported as norm-based values (NBS) and minimal clinically important difference (MCID) values for PCS and MCS (3 NBS points). RESU!

BACKGROUND: Adult spinal deformity is a prevalent cause of pain and disability. Established measures of sagittal spinopelvic alignment such as sagittal vertical axis and pelvic tilt can be modified by postural compensation, including pelvic retroversion, knee flexion, and the use of assistive devices for standing. We introduce the T1 pelvic angle, a novel measure of sagittal alignment that simultaneously accounts for both spinal inclination and pelvic retroversion. The purpose of this study was to investigate the relationship of the T1 pelvic angle and other established sagittal alignment measures and to correlate these parameters with health-related quality-of-life measures. METHODS: This is a multicenter, prospective, cross-sectional analysis of consecutive patients with adult spinal deformity. Inclusion criteria were adult spinal deformity, an age of greater than eighteen years, and any of the following: scoliosis, a Cobb angle of >/=20 degrees , sagittal vertical axis of >/=5 cm, thoracic kyphosis of >/=60 degrees , and pelvic tilt of >/=25 degrees . Clinical measures of disability included the Oswestry Disability Index (ODI), Scoliosis Research Society (SRS)-22, and Short Form-36 (SF-36) questionnaires. RESULTS: Five hundred and fifty-nine consecutive patients with adult spinal deformity (mean age, 52.5 years) were enrolled. The T1 pelvic angle correlated with the sagittal vertical axis (r = 0.837), pelvic incidence minus lumbar lordosis (r = 0.889), and pelvic tilt (0.933). Categorizing the patients by increasing T1 pelvic angle (<10 degrees , 10 degrees to 20 degrees , 21 degrees to 30 degrees , and >30 degrees ) revealed a significant and progressive worsening in health-related quality of life (p < 0.001 for all). The T1 pelvic angle and sagittal vertical axis correlated with the ODI (0.435 and 0.455), SF-36 Physical Component Summary (-0.445 and -0.458), and SRS (-0.358 and -0.383) (p < 0.001 for all). Utilizing a linear regression analysis, a T1 pelvic angle of 20 degrees corresponded to a severe disability (an ODI of >40), and the meaningful change in T1 pelvic angle corresponding to one minimal clinically important difference was 4.1 degrees on the ODI. CONCLUSIONS: The T1 pelvic angle correlates with health-related quality of life in patients with adult spinal deformity. The T1 pelvic angle is related to both pelvic tilt and sagittal vertical axis; however, unlike sagittal vertical axis, it does not vary on the basis of the extent of pelvic retroversion or patient support in standing. Since the T1 pelvic angle is an angular and not a linear measure, it does not require calibration of the radiograph. Thus, the T1 pelvic angle measures sagittal deformity independent of many postural compensatory mechanisms, and it can be useful as a preoperative planning tool, with a target T1 pelvic angle of <14 degrees . LEVEL OF EVIDENCE: Diagnostic Level II. See Instructions for Authors for a complete description of levels of evidence.

BACKGROUND: Animal spinal cord injury (SCI) models have proved invaluable in better understanding the mechanisms involved in traumatic SCI and evaluating the effectiveness of experimental therapeutic interventions. Over the past 25 years, substantial gains have been made in developing consistent, reproducible and reliable animal SCI models. STUDY DESIGN: Review. OBJECTIVE: The objective of this review was to consolidate current knowledge on SCI models and introduce newer paradigms that are currently being developed. RESULTS: SCI models are categorized based on the mechanism of injury into contusion, compression, distraction, dislocation, transection or chemical models. Contusion devices inflict a transient, acute injury to the spinal cord using a weight-drop technique, electromagnetic impactor or air pressure. Compression devices compress the cord at specific force and duration to cause SCI. Distraction SCI devices inflict graded injury by controlled stretching of the cord. Mechanical displacement of the vertebrae is utilized to produce dislocation-type SCI. Surgical transection of the cord, partial or complete, is particularly useful in regenerative medicine. Finally, chemically induced SCI replicates select components of the secondary injury cascade. Although rodents remain the most commonly used species and are best suited for preliminary SCI studies, large animal and nonhuman primate experiments better approximate human SCI. CONCLUSION: All SCI models aim to replicate SCI in humans as closely as possible. Given the recent improvements in commonly used models and development of newer paradigms, much progress is anticipated in the coming years.

The choice among the many options of approach and adjunct techniques in planning a posterior lumbar fusion can be problematic. Debates remain as to whether solid fusion has an advantage over pseudarthrosis regarding long-term symptom deterioration and whether an instrumented or a noninstrumented approach will best serve clinically and/or cost effectively, particularly in elderly patients. Increased motion resulting in higher rates of nonunion and the use of nonsteroidal anti-inflammatory drugs have been studied in animal models and are presumed risk factors, despite the lack of clinical investigation. Smoking is a proven risk factor for pseudarthrosis in both animal models and level III clinical studies. Recent long-term studies and image/clinical assessment of lumbar fusions and pseudarthrosis show that, although imaging remains a key area of difficulty in assessment, including an instrumented approach and a well-selected biologic adjunct, as well as achieving a solid fusion, all carry important long-term clinical advantages in avoiding revision surgery for nonunion.

To achieve optimal results after fusion for adolescent idiopathic scoliosis (AIS), radiographic parameters must be aligned with motion and performance. The effects of fusion on balance are poorly understood. Center of mass (COM) excursion and instantaneous interaction with center of pressure (COP) provides information about patients' balancing ability during gait. This study investigates the interaction between COM and COP (COM-COP) in AIS patients before and one year after spine fusion and determines what radiographic goals predict restoration of harmonious COM-COP. This was a prospective study that investigated sixteen adolescents with AIS curvature >30 requiring surgical correction. Clinical outcomes measures, X-rays, and 3D motion-capture gait analysis were collected. Sagittal and coronal COM and COP offsets and inclination angles were calculated from positional data. COM excursion was calculated as peak COM displacement based on mediolateral and vertical deviation from a line fitted to the patient's path. Radiographic parameters were measured to determine variables predictive of change in COM excursion. Post-operatively, average COM peak displacement decreased (42.6 to 13.1mm, p=0.001) and COM peak vertical displacement remained unchanged (17.0 to 16.3mm, p=0.472). COM-COP inclination angles reduced in the coronal, but not sagittal plane. Coronal lower extremity peak inclination angles reduced (8.8 to 7.5 , p=0.025), correlating with C7 plumb-line offset (R=0.581, p=0.018). Thoracic Cobb, thoracic kyphosis, and C7 plumb-line were predictors of change in COM excursion. Mediolateral COM excursion post-surgery may reflect an attempt to reduce kinetic demands with improved spinal alignment. Although AIS correction has historically focused on the coronal plane, sagittal parameters may be more important for motion than previously theorized.

STRUCTURED ABSTRACT: Study Design. Animal modelObjective. Determine whether Amicar and TXA inhibit spine fusion volumeSummary of Background Data. Amicar and TXA are antifibrinolytics used to reduce perioperative bleeding. Prior in vitro data showed that antifibrinolytics reduce osteoblast bone mineralization. This study tested whether antifibrinolytics Amicar and TXA inhibit spine fusion.Methods. Posterolateral L4-L6 fusion was performed in fifty mice, randomized into groups of ten, that received the following treatment before and after surgery: (1) Saline; (2) TXA 100mg/kg; (3) TXA 1000mg/kg; (4) Amicar 100 mg/kg; (5) Amicar 1000 mg/kg. High-resolution plane radiography was performed after 5 weeks and micro-CT was performed at the end of the 12-week study. Radiographs were graded using the Lenke scale. Micro-CT was used to quantify fusion mass bone volume. One-way analysis of variance (ANOVA) by ranks with Kruskal-Wallis testing was used to compare the radiographic scores. One-way ANOVA with least-significant differences (LSD) post-hoc testing was used to compare the micro-CT bone volume.Results. The average (+/- SD) bone volume/total volume (%) measured in the saline, TXA 100 mg/kg, TXA 1000 mg/kg, Amicar 100 mg/kg and Amicar 1000 mg/kg groups were 10.8+/-2.3, 9.7+/-2.2, 13.4+/-3.2, 15.5+/-5.2 and 17.9+/-3.5%, respectively. There was a significant difference in the Amicar 100 mg/kg (p < 0.05) and Amicar 1000 mg/kg (p < 0.001) groups compared to saline. There was greater bone volume in the Amicar groups compared to the TXA group (p < 0.001). There was more bone volume in the TXA 1000 mg/kg group compared to TXA 100 mg/kg (p < 0.05) but the bone volume in neither of the TXA groups was different to saline (p = 0.49). There were no between-group differences observed using plane radiographic scoring.Conclusions. Amicar significantly enhanced the fusion bone mass in a dose-dependent manner while TXA did not have a significant effect on fusion compared to saline control.These data are in contrast to prior in vitro data that antifibrinolytics inhibit osteoblast bone mineralization.

BACKGROUND: Postoperative venous thromboembolic events (VTEs), which include pulmonary emboli and deep venous thromboses, are potentially preventable causes of death. The aim of this study was to investigate the patient and procedure-related risk factors for the occurrence of VTEs in patients undergoing spinal fusion.METHODS: We used ICD-9-CM (International Classification of Diseases, 9th Revision, Clinical Modification) procedure codes to identify patients in the Nationwide Inpatient Sample (NIS) database for 2001 through 2010 who were treated with spinal fusion. The occurrence of a symptomatic VTE was identified with use of ICD-9-CM diagnosis codes. Patient demographics, hospital characteristics, and comorbidities in the VTE and non-VTE groups were analyzed, and independent risk factors for VTE were identified.RESULTS: A total of 710,154 spinal fusion procedures were identified in the NIS from 2001 to 2010, and 3525 (0.50%) of these patients were recorded as having 3777 VTEs, consisting of 2038 deep venous thromboses (0.29%) and 1739 pulmonary emboli (0.24%). Patients with a VTE were older on average (57.63 years compared with 52.88 years for patients without a VTE) and more often male (VTE incidence, 0.58% compared with 0.42% for female) and black (VTE incidence, 0.78% compared with 0.47% for white). Postoperative VTE occurrence was associated with a longer hospital stay (18.0 compared with 3.94 days) and higher total hospital charges ($207,253 compared with $66,823). A number of comorbidities and procedure-related factors were identified as independent risk factors for VTE.CONCLUSIONS: We present a VTE Risk Index, based on the independent risk factors identified in this study, for the VTE following spinal fusion. In conjunction with current guidelines, this risk index can be used to guide clinical decision-making regarding VTE prophylaxis in patients undergoing spinal fusion.LEVEL OF EVIDENCE: Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.