Accuracy of Stereovision-Updated Versus Preoperative CT-Based Image Guidance in Multilevel Lumbar Pedicle Screw Placement: A Cadaveric Swine Study.

Change in vertebral position between preoperative imaging and the surgical procedure reduces the accuracy of image-guided spinal surgery, requiring repeated imaging and surgical field registration, a process that takes time and exposes patients to additional radiation. We developed a handheld, camera-based, deformable registration system (intraoperative stereovision, iSV) to register the surgical field automatically and compensate for spinal motion during surgery without further radiation exposure. Methods: We measured motion-induced errors in image-guided lumbar pedicle screw placement in 6 whole-pig cadavers using state-of-the-art commercial spine navigation (StealthStation; Medtronic) and iSV registration that compensates for intraoperative vertebral motion. We induced spinal motion by using preoperative computed tomography (pCT) of the lumbar spine performed in the supine position with accentuated lordosis and performing surgery with the animal in the prone position. StealthStation registration of pCT occurred using metallic fiducial markers implanted in each vertebra, and iSV data were acquired to perform a deformable registration between pCT and the surgical field. Sixty-eight pedicle screws were placed in 6 whole-pig cadavers using iSV and StealthStation registrations in random order of vertebral level, relying only on image guidance without invoking the surgeon's judgment. The position of each pedicle screw was assessed with post-procedure CT and confirmed via anatomical dissection. Registration errors were assessed on the basis of implanted fiducials. Results: The frequency and severity of pedicle screw perforation were lower for iSV registration compared with StealthStation (97% versus 68% with Grade 0 medial perforation for iSV and StealthStation, respectively). Severe perforation occurred only with StealthStation (18% versus 0% for iSV). The overall time required for iSV registration (computational efficiency) was ∼10 to 15 minutes and was comparable with StealthStation registration (∼10 min). The mean target registration error was smaller for iSV relative to StealthStation (2.81 ± 0.91 versus 8.37 ± 1.76 mm). Conclusions: Pedicle screw placement was more accurate with iSV registration compared with state-of-the-art commercial navigation based on preoperative CT when alignment of the spine changed during surgery. Clinical Relevance: The iSV system compensated for intervertebral motion, which obviated the need for repeated vertebral registration while providing efficient, accurate, radiation-free navigation during open spinal surgery.

A level-wise spine registration framework to account for large pose changes.

PURPOSES: Accurate and efficient spine registration is crucial to success of spine image guidance. However, changes in spine pose cause intervertebral motion that can lead to significant registration errors. In this study, we develop a geometrical rectification technique via nonlinear principal component analysis (NLPCA) to achieve level-wise vertebral registration that is robust to large changes in spine pose. METHODS: We used explanted porcine spines and live pigs to develop and test our technique. Each sample was scanned with preoperative CT (pCT) in an initial pose and rescanned with intraoperative stereovision (iSV) in a different surgical posture. Patient registration rectified arbitrary spinal postures in pCT and iSV into a common, neutral pose through a parameterized moving-frame approach. Topologically encoded depth projection 2D images were then generated to establish invertible point-to-pixel correspondences. Level-wise point correspondences between pCT and iSV vertebral surfaces were generated via 2D image registration. Finally, closed-form vertebral level-wise rigid registration was obtained by directly mapping 3D surface point pairs. Implanted mini-screws were used as fiducial markers to measure registration accuracy. RESULTS: In seven explanted porcine spines and two live animal surgeries (maximum in-spine pose change of 87.5 mm and 32.7 degrees averaged from all spines), average target registration errors (TRE) of 1.70 ± 0.15 mm and 1.85 ± 0.16 mm were achieved, respectively. The automated spine rectification took 3-5 min, followed by an additional 30 secs for depth image projection and level-wise registration. CONCLUSIONS: Accuracy and efficiency of the proposed level-wise spine registration support its application in human open spine surgeries. The registration framework, itself, may also be applicable to other intraoperative imaging modalities such as ultrasound and MRI, which may expand utility of the approach in spine registration in general.

Hand-Held Stereovision System for Image Updating in Open Spine Surgery.

BACKGROUND: Image guidance in open spinal surgery is compromised by changes in spinal alignment between preoperative images and surgical positioning. We evaluated registration of stereo-views of the surgical field to compensate for vertebral alignment changes. OBJECTIVE: To assess accuracy and efficiency of an optically tracked hand-held stereovision (HHS) system to acquire images of the exposed spine during surgery. METHODS: Standard midline posterior approach exposed L1 to L6 in 6 cadaver porcine spines. Fiducial markers were placed on each vertebra as "ground truth" locations. Spines were positioned supine with accentuated lordosis, and preoperative computed tomography (pCT) was acquired. Spines were re-positioned in a neutral prone posture, and locations of fiducials were acquired with a tracked stylus. Intraoperative stereovision (iSV) images were acquired and 3-dimensional (3D) surfaces of the exposed spine were reconstructed. HHS accuracy was assessed in terms of distances between reconstructed fiducial marker locations and their tracked counterparts. Level-wise registrations aligned pCT with iSV to account for changes in spine posture. Accuracy of updated computed tomography (uCT) was assessed using fiducial markers and other landmarks. RESULTS: Acquisition time for each image pair was <1 s. Mean reconstruction time was <1 s for each image pair using batch processing, and mean accuracy was 1.2 ± 0.6 mm across 6 cases. Mean errors of uCT were 3.1 ± 0.7 and 2.0 ± 0.5 mm on the dorsal and ventral sides, respectively. CONCLUSION: Results suggest that a portable HHS system offers potential to acquire accurate image data from the surgical field to facilitate surgical navigation during open spine surgery.

Measuring protein biomarker concentrations using antibody tagged magnetic nanoparticles.

Under physiological conditions biomarker concentrations tend to rise and fall over time e.g. for inflammation. Ex vivo measurements provide a snapshot in time of biomarker concentrations, which is useful, but limited. Approaching real time monitoring of biomarker concentration(s) using a wearable, implantable or injectable in vivo sensor is therefore an appealing target. As an early step towards developing an in vivo biomarker sensor, antibody (AB) tagged magnetic nanoparticles (NPs) are used here to demonstrate the in vitro measurement of ~5 distinct biomarkers with high specificity and sensitivity. In previous work, aptamers were used to target a given biomarker in vitro and generate magnetic clusters that exhibit a characteristic rotational signature quite different from free NPs. Here the method is expanded to detect a much wider range of biomarkers using polyclonal ABs attached to the surface of the NPs. Commercial ABs exist for a wide range of targets allowing accurate and specific concentration measurements for most significant biomarkers. We show sufficient detection sensitivity, using an in-house spectrometer to measure the rotational signatures of the NPs, to assess physiological concentrations of hormones, cytokines and other signaling molecules. Detection limits for biomarkers drawn mainly from pain and inflammation targets were: 10 pM for mouse Granzyme B (mGZM-B), 40 pM for mouse interferon-gamma (mIFN-γ), 7 pM for mouse interleukin-6 (mIL-6), 40 pM for rat interleukin-6 (rIL-6), 40 pM for mouse vascular endothelial growth factor (mVEGF) and 250 pM for rat calcitonin gene related peptide (rCGRP). Much lower detection limits are certainly possible using improved spectrometers and nanoparticles.

Trends in Lumbar Fusion Procedure Rates and Associated Hospital Costs for Degenerative Spinal Diseases in the United States, 2004 to 2015.

STUDY DESIGN: Analysis of National Inpatient Sample (NIS), 2004 to 2015. OBJECTIVE: Describe recent trends in US rates of lumbar fusion procedures and associated costs, by surgical indication. SUMMARY OF BACKGROUND DATA: Spinal fusion is appropriate for spinal deformity and instability, but evidence of effectiveness is limited for primary disc herniation and spinal stenosis without instability. It remains controversial for treatment of axial pain secondary to degenerative disc disease. There are potential non-instability, non-deformity indications for fusion surgery, including but not limited to severe foraminal stenosis and third-time disc herniation. METHODS: Elective lumber fusion trends were reported using Poisson regression, grouped by indication as degenerative scoliosis, degenerative spondylolisthesis, spinal stenosis, disc herniation, and disc degeneration. Generalize linear regression was used to estimate trends in hospital costs, adjusted for age, sex, indication, comorbidity, and inflation. RESULTS: Volume of elective lumbar fusion increased 62.3% (or 32.1% per 100,000 US adults), from 122,679 cases (60.4 per 100,000) in 2004 to 199,140 (79.8 per 100,000) in 2015. Increases were greatest among age 65 or older, increasing 138.7% by volume (73.2% by rate), from 98.3 per 100,000 (95% confidence interval [CI] 97.2, 99.3) in 2004 to 170.3 (95% CI 169.2, 171.5) in 2015. Although the largest increases were for spondylolisthesis (+47,390 operations, 111%) and scoliosis (+16,129 operations, 186.6%), disc degeneration, herniation, and stenosis combined to accounted for 42.3% of total elective lumbar fusions in 2015. Aggregate hospital costs increased 177% during these 12 years, exceeding $10 billion in 2015, and averaging more than $50,000 per admission. CONCLUSION: While the prevalence of spinal pathologies is not known, the rate of elective lumbar fusion surgery in the United States increased most for spondylolisthesis and scoliosis, indications with relatively good evidence of effectiveness. The proportion of fusions coded for indications with less evidence of effectiveness has slightly decreased in the most recent years. LEVEL OF EVIDENCE: 3.

Understanding the value of minimally invasive procedures for the treatment of lumbar spinal stenosis: the case of interspinous spacer devices.

BACKGROUND CONTEXT: Minimally invasive lumbar spinal stenosis procedures have uncertain long-term value. PURPOSE: This study sought to characterize factors affecting the long-term cost-effectiveness of such procedures using interspinous spacer devices ("spacers") relative to decompression surgery as a case study. STUDY DESIGN: Model-based cost-effectiveness analysis. PATIENT SAMPLE: The Medicare Provider Analysis and Review database for the years 2005-2009 was used to model a group of 65-year-old patients with spinal stenosis who had no previous spine surgery and no contraindications to decompression surgery. OUTCOME MEASURES: Costs, quality-adjusted life years (QALYs), and cost per QALY gained were the outcome measures. METHODS: A Markov model tracked health utility and costs over 10 years for a 65-year-old cohort under three care strategies: conservative care, spacer surgery, and decompression surgery. Incremental cost-effectiveness ratios (ICER) reported as cost per QALY gained included direct medical costsfor surgery. Medicare claims data were used to estimate complication rates, reoperation, and related costs within 3 years. Utilities and long-term reoperation rates for decompression were derived frompublished studies. Spacer failure requiring reoperation beyond 3 years and post-spacer health utilities are uncertain and were evaluated through sensitivity analyses. In the base-case, the spacer failure rate was held constant for years 4-10 (cumulative failure: 47%). In a "worst-case" analysis, the 10-year cumulative reoperation rate was increased steeply (to 90%). Threshold analyses were performed to determine the impact of failure and post-spacer health utility on the cost-effectiveness of spacer surgery. RESULTS: The spacer strategy had an ICER of $89,500/QALY gained under base-case assumptions, and remained under $100,000 as long as the 10-year cumulative probability of reoperation did not exceed 54%. Under worst-case assumptions, the spacer ICER was $482,000/QALY and fell below $100,000 only if post-spacer utility was 0.01 greater than post-decompression utility or the cost of spacer surgery was $1,600 less than the cost of decompression surgery. CONCLUSIONS: Spacers may provide a reasonably cost-effective initial treatment option for patients with lumbar spinal stenosis. Their value is expected to improve if procedure costs are lower in outpatient settings where these procedures are increasingly being performed. Decision analysis is useful for characterizing the long-term cost-effectiveness potential for minimally invasive spinal stenosis treatments and highlights the importance of complication rates and prospective health utility assessment.

Early Effects of Medicare's Bundled Payment for Care Improvement Program for Lumbar Fusion.

STUDY DESIGN: Retrospective analysis of Medicare claims linked to hospital participation in the Center for Medicare and Medicaid Innovation's episode-based Bundled Payment for Care Improvement (BPCI) program for lumbar fusion. OBJECTIVE: To describe the early effects of BPCI participation for lumbar fusion on 90-day reimbursement, procedure volume, reoperation, and readmission. SUMMARY OF BACKGROUND DATA: Initiated on January 1, 2013, BPCI's voluntary bundle payment program provides a predetermined payment for services related to a Diagnosis-Related Group-defined "triggering event" over a defined time period. As an alternative to fee-for-service, these reforms shift the financial risk of care on to hospitals. METHODS: We identified fee-for-service beneficiaries over age 65 undergoing a lumbar fusion in 2012 or 2013, corresponding to the years before and after BPCI initiation. Hospitals were grouped based on program participation status as nonparticipants, preparatory, or risk-bearing. Generalized estimating equation models adjusting for patient age, sex, race, comorbidity, and hospital size were used to compare changes in episode costs, procedure volume, and safety indicators based on hospital BPCI participation. RESULTS: We included 89,605 beneficiaries undergoing lumbar fusion, including 36% seen by a preparatory hospital and 7% from a risk-bearing hospital. The mean age of the cohort was 73.4 years, with 59% women, 92% White, and 22% with a Charlson Comorbidity Index of 2 or more. Participant hospitals had greater procedure volume, bed size, and total discharges. Relative to nonparticipants, risk-bearing hospitals had a slightly increased fusion procedure volume from 2012 to 2013 (3.4% increase vs. 1.6% decrease, P = 0.119), did not reduce 90-day episode of care costs (0.4% decrease vs. 2.9% decrease, P = 0.044), increased 90-day readmission rate (+2.7% vs. -10.7%, P = 0.043), and increased repeat surgery rates (+30.6% vs. +7.1% points, P = 0.043). CONCLUSION: These early, unintended trends suggest an imperative for continued monitoring of BPCI in lumbar fusion. LEVEL OF EVIDENCE: 3.

Use of Stereovision for Intraoperative Coregistration of a Spinal Surgical Field: A Human Feasibility Study.

BACKGROUND: The use of image guidance during spinal surgery has been limited by several anatomic factors such as intervertebral segment motion and ineffective spine immobilization. In its current form, the surgical field is coregistered with a preoperative computed tomography (CT), often obtained in a different spinal confirmation, or with intraoperative cross-sectional imaging. Stereovision offers an alternative method of registration. OBJECTIVE: To demonstrate the feasibility of stereovision-mediated coregistration of a human spinal surgical field using a proof-of-principle study, and to provide preliminary assessments of the technique's accuracy. METHODS: A total of 9 subjects undergoing image-guided pedicle screw placement also underwent stereovision-mediated coregistration with preoperative CT imaging. Stereoscopic images were acquired using a tracked, calibrated stereoscopic camera system mounted on an operating microscope. Images were processed, reconstructed, and segmented in a semi-automated manner. A multistart registration of the reconstructed spinal surface with preoperative CT was performed. Registration accuracy, measured as surface-to-surface distance error, was compared between stereovision registration and a standard registration. RESULTS: The mean surface reconstruction error of the stereovision-acquired surface was 2.20 ± 0.89 mm. Intraoperative coregistration with stereovision was performed with a mean error of 1.48 ± 0.35 mm compared to 2.03 ± 0.28 mm using a standard point-based registration method. The average computational time for registration with stereovision was 95 ± 46 s (range 33-184 s) vs 10to 20 min for standard point-based registration. CONCLUSION: Semi-automated registration of a spinal surgical field using stereovision is possible with accuracy that is at least comparable to current landmark-based techniques.

Validation of Using Claims Data to Measure Safety of Lumbar Fusion Surgery.

STUDY DESIGN: Retrospective analysis of patients undergoing elective lumbar fusion operations, comparing rates of repeat spine surgery based on method of ascertainment. OBJECTIVE: We report the accuracy of a claims-based approach for reporting repeat surgery compared with medical records abstraction as the "gold standard." SUMMARY OF BACKGROUND DATA: Previous studies have reported the validity of a claims-based algorithm for grouping patients by surgical indication and classifying operative features, but their accuracy in measuring surgical quality indicators has not been widely examined. METHODS: We identified a subset of patients undergoing elective lumbar fusion operations at a single institution from 1996 to 2011, excluding those with spinal fracture, spinal cord injury, or cancer. From the medical record we abstracted the incidence of repeat spine operation or rehospitalization at 1 year. We cross-classified each event record with its corresponding value derived from claims. The sensitivity and specificity of the claims-based approach were calculated for reoperation within 30, 90, and 365 days, and all-cause hospital readmission within 30 days. RESULTS: Medical records linked to claims data were obtained for 520 patients undergoing elective lumbar fusion. Reoperation rates based on chart review were 1.0%, 1.3%, 3.6%, compared with 0.8%, 1.7%, and 3.8% based on the final claims methods at 30, 90, and 365 days, respectively. The claims-based algorithm had sensitivities of 80.0%, 100%, and 94.1% and specificities of 100%, 99.6%, 99.2% for repeat surgery within 30, 90, and 365 days, respectively. The sensitivity for all-cause readmission was 50%. CONCLUSION: Health care quality improvement efforts often rely on administrative data to report surgical safety. We found that claims-based ascertainment of safety at a single institution was very accurate. However, accuracy depended on careful attention to the timing of outcomes, as well as the definitions and coding of repeat surgery, including how orthopedic device removal codes are classified. LEVEL OF EVIDENCE: 3.

Bone Morphogenetic Protein Use and Cancer Risk Among Patients Undergoing Lumbar Arthrodesis: A Case-Cohort Study Using the SEER-Medicare Database.

BACKGROUND: Recombinant bone morphogenetic proteins (BMPs) are growth factors utilized in lumbar arthrodeses. Limited data from randomized trials suggest that BMP may increase cancer risk. We sought to evaluate cancer risk and mortality following the use of BMP in lumbar arthrodesis. METHODS: Within the linked Surveillance, Epidemiology, and End Results (SEER) Program-Medicare cohort, we conducted a case-cohort study of 7,278 individuals who were ≥65 years of age and had undergone a lumbar arthrodesis from 2004 to 2011. Of these patients, 3,627 were individuals in a 5% random subcohort of Medicare enrollees in SEER areas including 191 who developed cancer, and there were 3,651 individuals outside the subcohort who developed cancer. Weighted Cox proportional-hazards regression was used to estimate hazard ratios (HRs) and 95% confidence intervals (95% CIs) for cancer on the basis of exposure to BMP. RESULTS: In the SEER-Medicare subcohort, 30.7% of individuals who underwent a lumbar arthrodesis received BMP. BMP was not associated with overall cancer risk in univariate analyses (HR, 0.92 [95% CI, 0.82 to 1.02]) or after adjustment for demographic characteristics, comorbidities, hospital size, history of cancer, and calendar year (adjusted HR, 0.94 [95% CI, 0.84 to 1.05]). Individual cancer types were also not significantly elevated (p > 0.05 for all) in BMP users compared with nonusers. In addition, BMP use was not associated with a new cancer in people who had cancer prior to undergoing lumbar arthrodesis (adjusted HR, 1.04 [95% CI, 0.71 to 1.52]) or with mortality after a cancer diagnosis (adjusted HR, 1.05 [95% CI, 0.93 to 1.19]). CONCLUSIONS: In a large population of elderly U.S. adults undergoing lumbar arthrodesis, BMP use was not associated with cancer risk or mortality. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

C2 Vertebral Fractures in the Medicare Population: Incidence, Outcomes, and Costs.

BACKGROUND: Cervical 2 (C2) fractures in the elderly are common, and the incidence of these fractures has been increasing. Surgical and nonoperative treatments are associated with high complication and mortality rates, and these rates have not been evaluated at the population level, to our knowledge. The purpose of this study was to use the Medicare claims database to determine trends in treatment, surgical and nonoperative outcomes, and Medicare reimbursement for treatment of these fractures. METHODS: We examined the Medicare claims database from 2000 to 2011 to identify patients admitted for the treatment of a C2 fracture. The incidence of fractures and the rates of nonoperative and surgical treatment were determined across the study period. We compared rates of mortality and life-threatening complications between patients treated nonoperatively and surgically. Centers for Medicare & Medicaid Services (CMS) payments for the initial admission as well as for subsequent inpatient admissions during the ninety-day post-admission period were compared between treatment groups. We used multivariate analysis to control for differences in patient characteristics between groups. RESULTS: There were 81,596 admissions for C2 fracture identified, and 53,338 met inclusion criteria. The incidence of C2 fractures increased 135% from 2000 to 2011, but the rate of surgical treatment remained constant at 16%. There was significantly lower mortality at thirty days for the surgical group at 8.3% compared with the nonoperative group at 16.2% (p < 0.001) and at one year for the surgical group at 21.7% compared with the nonoperative group at 32.3% (p < 0.001). Life-threatening complications within thirty days of admission were slightly more common in the surgical group at 10.9% compared with the nonoperative group at 9.0% (p < 0.05). Medicare reimbursements for the initial inpatient admission were significantly higher (p < 0.001) in U.S. dollars for the surgical group at $21,487 compared with the nonoperative group at $8469, and this significant difference (p < 0.001) persisted in the ninety-day post-discharge period at $10,487 for the surgical group compared with $8410 for the nonoperative group. CONCLUSIONS: Although the incidence of C2 fractures in the Medicare population increased from 2000 to 2011, the rate of surgery stayed relatively constant. After controlling for baseline differences, patients treated with surgery had significantly lower thirty-day and one-year mortality rates compared with patients treated nonoperatively. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.

Effects of a Commercial Insurance Policy Restriction on Lumbar Fusion in North Carolina and the Implications for National Adoption.

STUDY DESIGN: An analysis of the State Inpatient Database of North Carolina, 2005 to 2012, and the Nationwide Inpatient Sample, including all inpatient lumbar fusion admissions from nonfederal hospitals. OBJECTIVE: The aim of the study was to examine the influence of a major commercial policy change that restricted lumbar fusion for certain indications and to forecast the potential impact if the policy were adopted nationally. SUMMARY OF BACKGROUND DATA: Few studies have examined the effects of recent changes in commercial coverage policies that restrict the use of lumbar fusion. METHODS: We included adults undergoing elective lumbar fusion or re-fusion operations in North Carolina. We aggregated data into a monthly time series to report changes in the rates and volume of lumbar fusion operations for disc herniation or degeneration, spinal stenosis, spondylolisthesis, or revision fusions. Time series regression models were used to test for significant changes in the use of fusion operation following a major commercial coverage policy change initiated on January 1, 2011. RESULTS: There was a substantial decline in the use of lumbar fusion for disc herniation or degeneration following the policy change on January 1, 2011. Overall rates of elective lumbar fusion operations in North Carolina (per 100,000 residents) increased from 103.2 in 2005 to 120.4 in 2009, before declining to 101.9 by 2012. The population rate (per 100,000 residents) of fusion among those under age 65 increased from 89.5 in 2005 to 101.2 in 2009, followed by a sharp decline to 76.8 by 2012. There was no acceleration in the already increasing rate of fusion for spinal stenosis, spondylolisthesis, or revision procedures, but there was a coincident increase in decompression without fusion. CONCLUSION: This commercial insurance policy change had its intended effect of reducing fusion operations for indications with less evidence of effectiveness without changing rates for other indications or resulting in an overall reduction in spine surgery. Nevertheless, broader adoption of the policy could significantly reduce the national rates of fusion operations and associated costs. LEVEL OF EVIDENCE: 3.

Intraoperative CT as a registration benchmark for intervertebral motion compensation in image-guided open spinal surgery.

PURPOSE: An accurate and reliable benchmark of registration accuracy and intervertebral motion compensation is important for spinal image guidance. In this study, we evaluated the utility of intraoperative CT (iCT) in place of bone-implanted screws as the ground-truth registration and illustrated its use to benchmark the performance of intraoperative stereovision (iSV). METHODS: A template-based, multi-body registration scheme was developed to individually segment and pair corresponding vertebrae between preoperative CT and iCT of the spine. Intervertebral motion was determined from the resulting vertebral pair-wise registrations. The accuracy of the image-driven registration was evaluated using surface-to-surface distance error (SDE) based on segmented bony features and was independently verified using point-to-point target registration error (TRE) computed from bone-implanted mini-screws. Both SDE and TRE were used to assess the compensation accuracy using iSV. RESULTS: The iCT-based technique was evaluated on four explanted porcine spines (20 vertebral pairs) with artificially induced motion. We report a registration accuracy of 0.57 [Formula: see text] 0.32 mm (range 0.34-1.14 mm) and 0.29 [Formula: see text] 0.15 mm (range 0.14-0.78 mm) in SDE and TRE, respectively, for all vertebrae pooled, with an average intervertebral rotation of [Formula: see text] (range 1.5[Formula: see text]-7.9[Formula: see text]). The iSV-based compensation accuracy for one sample (four vertebrae) was 1.32 [Formula: see text] 0.19 mm and 1.72 [Formula: see text] 0.55 mm in SDE and TRE, respectively, exceeding the recommended accuracy of 2 mm. CONCLUSION: This study demonstrates the effectiveness of iCT in place of invasive fiducials as a registration ground truth. These findings are important for future development of on-demand spinal image guidance using radiation-free images such as stereovision and ultrasound on human subjects.

Patient Registration Using Intraoperative Stereovision in Image-guided Open Spinal Surgery.

Despite its widespread availability and success in open cranial neurosurgery, image-guidance technology remains more limited in use in open spinal procedures, in large part, because of patient registration challenges. In this study, we evaluated the feasibility of using intraoperative stereovision (iSV) for accurate, efficient, and robust patient registration in an open spinal fusion surgery. Geometrical surfaces of exposed vertebrae were first reconstructed from iSV. A classical multistart registration was then executed between point clouds generated from iSV and preoperative computed tomography images of the spine. With two pairs of feature points manually identified to facilitate the registration, an average registration accuracy of 1.43 mm in terms of surface-to-surface distance error was achieved in eight patient cases using a single iSV image pair sampling 2-3 vertebral segments. The iSV registration error was consistently smaller than the conventional landmark approach for every case (average of 2.02 mm with the same error metric). The large capture ranges (average of 23.8 mm in translation and 46.0° in rotation) found in the iSV patient registration suggest the technique may offer sufficient robustness for practical application in the operating room. Although some manual effort was still necessary, the manually-derived inputs for iSV registration only needed to be approximate as opposed to be precise and accurate for the manual efforts required in landmark registration. The total computational cost of the iSV registration was 1.5 min on average, significantly less than the typical ∼30 min required for the landmark approach. These findings support the clinical feasibility of iSV to offer accurate, efficient, and robust patient registration in open spinal surgery, and therefore, its potential to further increase the adoption of image guidance in this surgical specialty.

SPORT: Does incidental durotomy affect longterm outcomes in cases of spinal stenosis?

BACKGROUND: Incidental durotomy is a familiar encounter during surgery for lumbar spinal stenosis. The impact of durotomy on long-term outcomes remains a matter of debate. OBJECTIVE: To determine the impact of durotomy on the long-term outcomes of patients in the Spine Patient Outcomes Research Trial (SPORT). METHODS: The SPORT cohort participants with a confirmed diagnosis of spinal stenosis, without associated spondylolisthesis, undergoing standard, first-time, open decompressive laminectomy, with or without fusion, were followed up from baseline at 6 weeks, and 3, 6, and 12 months and yearly thereafter at 13 spine clinics in 11 US states. Patient data from this prospectively gathered database were reviewed. As of May 2009, the mean follow-up among all analyzed patients was 43.8 months. RESULTS: Four hundred nine patients underwent first-time open laminectomy with or without fusion. Thirty-seven of these patients (9%) had an incidental durotomy. No significant differences were observed with or without durotomy in age; sex; race; body mass index; the prevalence of smoking, diabetes mellitus, and hypertension; decompression level; number of levels decompressed; or whether an additional fusion was performed. The durotomy group had significantly increased operative duration, operative blood loss, and inpatient stay. There were, however, no differences in incidence of nerve root injury, mortality, additional surgeries, or primary outcomes (Short Form-36 Bodily Pain or Physical Function scores or Oswestry Disability Index) at yearly follow-ups to 4 years. CONCLUSIONS: Incidental durotomy during first-time lumbar laminectomy for spinal stenosis did not impact long-term outcomes in affected patients.

Use of bone morphogenetic protein among patients undergoing fusion for degenerative diagnoses in the United States, 2002 to 2012.

BACKGROUND CONTEXT: Use of bone morphogenetic protein (BMP) as an adjunct to spinal fusion surgery proliferated after Food and Drug Administration (FDA) approval in 2002. Major safety concerns emerged in 2008. PURPOSE: The purpose of this study was to examine whether published concerns about the safety of BMP altered clinical practice. STUDY DESIGN/SETTING: The study design involved the analysis of the National Inpatient Sample from 2002 through 2012. PATIENT SAMPLE: Adults (older than 20 years) undergoing an elective fusion operation for common degenerative diagnoses were identified using codes from the International Classification of Diseases, ninth revision, Clinical Modification. OUTCOME MEASURES: Outcome measures were proportion of cervical and lumbar fusion operations, over time, that involved BMP. METHODS: We aggregated the data into a monthly time series and reported the proportion of cervical and lumbar fusion operations, over time, that involved BMP. Autoregressive Integrated Moving Average, a regression model for time series data, was used to test whether there was a statistically significant change in the overall rate of BMP use after an FDA Public Health Notification in 2008. RESULTS: Use of BMP in spinal fusion procedures increased rapidly until 2008, involving up to 45.2% of lumbar and 13.5% of cervical fusions. Bone morphogenetic protein use significantly decreased after the 2008 FDA Public Health Notification and revelations of financial payments to surgeons involved in the pivotal FDA-approved trials. For lumbar fusion, the average annual increase was 7.9 percentage points per year from 2002 to 2008, followed by an average annual decrease of 11.7 percentage points thereafter (p≤.001). Use of BMP in cervical fusion increased 2.0% per year until the FDA Public Health Notification, followed by a 2.8% per year decrease (p=.035). CONCLUSIONS: Use of BMP in spinal fusion surgery declined subsequent to published safety concerns and revelations of financial conflicts of interest for investigators involved in the pivotal clinical trials.

The SPORT value compass: do the extra costs of undergoing spine surgery produce better health benefits?

BACKGROUND: The Spine Patient Outcomes Research Trial aimed to determine the comparative effectiveness of surgical care versus nonoperative care by measuring longitudinal values: outcomes, satisfaction, and costs. METHODS: This paper aims to summarize available evidence from the Spine Patient Outcomes Research Trial by addressing 2 important questions about outcomes and costs for 3 types of spine problem: (1) how do outcomes and costs of spine patients differ depending on whether they are treated surgically compared with nonoperative care? (2) What is the incremental cost per quality adjusted life year for surgical care over nonoperative care? RESULTS: After 4 years of follow-up, patients with 3 spine conditions that may be treated surgically or nonoperatively have systematic differences in value endpoints. The average surgical patient enjoys better health outcomes and higher treatment satisfaction but incurs higher costs. CONCLUSIONS: Spine care is preference sensitive and because outcomes, satisfaction, and costs vary over time and between patients, data on value can help patients make better-informed decisions and help payers know what their dollars are buying.

Developing a toolkit for comparing safety in spine surgery.

Safety information in spine surgery is important for informed patient choice and performance-based payment incentives, but measurement methods for surgical safety assessment are not standardized. Published reports of complication rates for common spinal procedures show wide variation. Factors influencing variation may include differences in safety ascertainment methods and procedure types. In a prospective cohort study, adverse events were observed in all patients undergoing spine surgery at two hospitals during a 2-year period. Multiple processes for adverse occurrence surveillance were implemented, and the associations between surveillance methods, surgery invasiveness, and observed frequencies of adverse events were examined. The study enrolled 1,723 patients. Adverse events were noted in 48.3% of the patients. Reviewers classified 25% as minor events and 23% as major events. Of the major events, the daily rounding team reported 38.4% of the events using a voluntary reporting system, surgeons reported 13.4%, and 9.1% were identified during clinical conferences. A review of medical records identified 86.7% of the major adverse events. The adverse events occurred during the inpatient hospitalization for 78.1% of the events, within 30 days for an additional 12.5%, and within the first year for the remaining 9.4%. A unit increase in the invasiveness index was associated with an 8.2% increased risk of a major adverse event. A Current Procedural Terminology-based algorithm for quantifying invasiveness correlated well with medical records-based assessment. Increased procedure invasiveness is associated with an increased risk of adverse events. The observed frequency of adverse events is influenced by the ascertainment modality. Voluntary reports by surgeons and other team members missed more than 50% of the events identified through a medical records review. Increased surgery invasiveness, measured from medical records or billing codes, is quantitatively associated with an increased risk of adverse events.

Indications for spine surgery: validation of an administrative coding algorithm to classify degenerative diagnoses.

STUDY DESIGN: Retrospective analysis of Medicare claims linked to a multicenter clinical trial. OBJECTIVE: The Spine Patient Outcomes Research Trial (SPORT) provided a unique opportunity to examine the validity of a claims-based algorithm for grouping patients by surgical indication. SPORT enrolled patients for lumbar disc herniation, spinal stenosis, and degenerative spondylolisthesis. We compared the surgical indication derived from Medicare claims with that provided by SPORT surgeons, the "gold standard." SUMMARY OF BACKGROUND DATA: Administrative data are frequently used to report procedure rates, surgical safety outcomes, and costs in the management of spinal surgery. However, the accuracy of using diagnosis codes to classify patients by surgical indication has not been examined. METHODS: Medicare claims were link to beneficiaries enrolled in SPORT. The sensitivity and specificity of 3 claims-based approaches to group patients on the basis of surgical indications were examined: (1) using the first listed diagnosis; (2) using all diagnoses independently; and (3) using a diagnosis hierarchy on the basis of the support for fusion surgery. RESULTS: Medicare claims were obtained from 376 SPORT participants, including 21 with disc herniation, 183 with spinal stenosis, and 172 with degenerative spondylolisthesis. The hierarchical coding algorithm was the most accurate approach for classifying patients by surgical indication, with sensitivities of 76.2%, 88.1%, and 84.3% for disc herniation, spinal stenosis, and degenerative spondylolisthesis cohorts, respectively. The specificity was 98.3% for disc herniation, 83.2% for spinal stenosis, and 90.7% for degenerative spondylolisthesis. Misclassifications were primarily due to codes attributing more complex pathology to the case. CONCLUSION: Standardized approaches for using claims data to group patients accurately by surgical indications have widespread interest. We found that a hierarchical coding approach correctly classified more than 90% of spine patients into their respective SPORT cohorts. Therefore, claims data seem to be a reasonably valid approach to classifying patients by surgical indication. LEVEL OF EVIDENCE: 3.