Quantitative Assessment of Myelopathy Patients Using Motor Evoked Potentials Produced by Transcranial Magnetic Stimulation

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Proceedings of the NASS 25th Annual Meeting / The Spine Journal 10 (2010) 1S–149S

assessment of vertebrae endplate stiffness at discrete sites before surgery would allow improve postoperative outcome. PURPOSE: To test hypothesis: 1) human lumbar vertebrae endplate strength topography depends on the 3-dimentional structural features of the vertebral body; 2) strength of human lumbar vertebrae endplate at discrete sites can be evaluated using models based on bone characteristics obtained from quantitative computer tomography images. STUDY DESIGN/SETTING: Basic research experimental study. PATIENT SAMPLE: Eight vertebrae (6- L5 and 2 L4) from 6 subjects (5 male and 1 female; age 54–78 years) were studied. OUTCOME MEASURES: Correlations between bone stiffness and micro-CT characteristics at tested sites. METHODS: Stiffness (N/mm) was assessed at 9 discrete sites of cranial and caudal surfaces by indentation test (IT). Tested sites were defined according to specially developed Cartesian map system. Before and after the IT microCT scanning of each vertebra was performed. Micro-CT characteristic of cortical and cancellous bone were defined at each region of interest (ROI) defined by a 3-dimentional coordinate system including: endplate thickness (mm), endplate density (mg/cc), trabecular thickness (mm), trabecular density (mg/cc), trabeculae separation (mm), trabecular number (/mm), cortical shell thickness (mm), cortical shell bone density, mg/cc. Osteoporotic status of the vertebrae was defined using QCT criteria. Predictive models of the local stiffness were created using bone structural and density characteristics. RESULTS: Stiffness across tested surfaces was highly variable and was significantly decreased in osteoporotic vertebrae. Endplate thickness and density combined with trabecular density and trabecular number of adjacent cancellous bone were found to be good predictors of local stiffness. Three models based on different combinations of bone structural characteristics were created. The average square root error was 620 N/mm, the 95% CI was639.4 N/mm. Predictive values (R2) of the created models were in range of 0.72–0.92. CONCLUSIONS: Obtained results confirm the study hypothesis that stiffness at discrete sites of human lumbar vertebrae depends on 3-dementional structure and density of the cortical and cancellous bone and that local stiffness can be evaluated using models based on vertebrae bone characteristics obtained from quantitative computed tomography images. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. doi: 10.1016/j.spinee.2010.07.289

P14. Development and Validation of a Noninvasive Spinal Motion Measurement System Shaun K. Stinton, MS1, R. Carter Cassidy, MD1, Robert Shapiro, PhD1, David Mullineaux, PhD1, David Pienkowski, PhD, MBA1, William Shaffer, MD2; 1University of Kentucky, Lexington, KY, USA; 2Northwest Iowa Bone, Joint & Sports, Spencer, IA, USA BACKGROUND CONTEXT: 750,000 Americans are estimated to suffer one or more spinal fractures each year due to osteoporosis and 25% of people who suffer a vertebral fracture will suffer another vertebral fracture within 5 years. It is probable that static (posture) and dynamic (gait) related abnormal loading of the spine interact with age-weakened tissue to produce a series of degenerative effects that culminate in disc degeneration and spine fractures. To reduce the incidence and severity of spontaneous vertebral compression fractures, it is first necessary to identify motion and postural patterns that could lead to increased loading of the vertebrae resulting in fractures over time. PURPOSE: To examine the feasibility of an accurate, non-invasive spinal motion measurement system that could be used to determine abnormal spinal motion. Future fractures could be predicted and prevented in subjects deemed to be at risk for fracture. STUDY DESIGN/SETTING: Cadaver torsos were used to compare motion measured by markers attached to bone pins and markers placed adhesively to the skin to determine the effect of skin sliding on vertebral motion.

PATIENT SAMPLE: Three cadaver torsos were tested. METHODS: Bone pins were implanted into 4 levels of the cadaver spines (T7, T12, L3, L5). The T7 level had 2 pins implanted. Retroreflective 4 mm marker triads were attached to the bone pins and additional marker triads were placed adhesively on the skin over the spinous process of the same vertebral levels (Figure 1). The instrumented torso was attached to a testing fixture with metal bands that wrapped around metal bars on the fixture and through the obturator foramen of the pelvis. The fixture allowed for flexion/extension, lateral bending, and axial rotation. Digital cameras with were used to record the 3D coordinates of the markers throughout the motion. Software was used to calculate the 3D angles of each vertebra throughout the entire motion relative to the lab axis. The x, y, and z axes represent roll, pitch and yaw. The angles between the pin and skin triads were compared to determine the accuracy of using skin markers versus the gold standard of bone pins. RESULTS: The average differences between the joint angle measured by the skin and pin marker triads were generally less that 0.5 degrees for around the x and y axes and less than 0.9 degrees around the z axis. The shape matching between the skin and pin curves in the angle plots was good in almost every case even in trials with larger differences between pin and skin marker angles. CONCLUSIONS: This research shows a potential method for spinal motion measurement and the accuracy to which the motion of the vertebrae can be determined. The results are promising in that skin markers provide an accurate representation of vertebral motion in cadaver torsos. Based on the results of the cadaver study, testing will be completed using the same skin markers on human subjects. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. doi: 10.1016/j.spinee.2010.07.290

P15. Quantitative Assessment of Myelopathy Patients Using Motor Evoked Potentials Produced by Transcranial Magnetic Stimulation Toshio Nakamae1, Nobuhiro Tanaka, MD1, Kazuyoshi Nakanishi, MD, PhD1, Yoshinori Fujimoto, MD2, Naosuke Kamei, MD, PhD1, Risako Yamamoto, MD1, Bunichiro Izumi, MD1, Yuki Fujioka, MD1, Ryo Ohta, MD1, Mitsuo Ochi, MD1; 1Department of Orthopedic Surgery, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan; 2Department of Orthopedic Surgery, Hiroshima General Hospital, Hatsukaichi, Japan BACKGROUND CONTEXT: In the diagnosis of myelopathy, conventional diagnostic methods such as neurologic findings, image study such as MRI and myelograms are usually performed, but conclusive diagnosis is sometimes difficult because many symptoms tend to be separate from the existing disease. And the MR images demonstrate morphological abnormalities of the cord but not functional impairment, and not all cord compression shown by MR images is associated with cord dysfunction. Transcranial magnetic stimulation (TMS) is applied as a quick and noninvasive technique to study conduction in the descending corticospinal pathways. Motor evoked potentials (MEPs) study using TMS may give a functional assessment of corticospinal conduction. But there are no large studies about MEPs using TMS in myelopathy patients. PURPOSE: The purpose of this study is to confirm the usefulness of MEPs for the assessment of the myelopathy and to investigate the use of MEPs using TMS as a screening tool for myelopathy. STUDY DESIGN/SETTING: Retrospective study. PATIENT SAMPLE: Eight hundred thirty-one patients with symptoms and signs suggestive of myelopathy were evaluated. OUTCOME MEASURES: MEP latency and central motor conduction time (CMCT) using transcranial magnetic brain stimulation were measured. METHODS: The MEPs from the abductor digiti minimi (ADM) and abductor hallucis (AH) muscles were evoked by transcranial magnetic brain

All referenced figures and tables will be available at the Annual Meeting and will be included with the post-meeting online content.

Proceedings of the NASS 25th Annual Meeting / The Spine Journal 10 (2010) 1S–149S stimulation. CMCT is calculated by subtracting the peripheral conduction time from the MEP latency. Later, 349 patients had surgery for myelopathy (operative group) and 482 patients were treated conservatively (nonoperative group). CMCTs in the operative group and nonoperative group were assessed. RESULTS: MEPs were prolonged in 711 patients (86%) and CMCTs were prolonged in 493 patients (59%) compared with the control patients. CMCTs from the ADM and AH in the operative group were significantly more prolonged than that in the nonoperative group. All patients in the operative group showed prolongation of MEPs or CMCTs or multiphase of the MEP wave. There were no complications concerning the examination. CONCLUSIONS: MEP studies using TMS have been reported as a quantitative and noninvasive evaluation of the descending corticospinal pathways. With the evidence provided by this large study presenting with symptoms and signs suggestive of myelopathy, MEPs were prolonged in 711 patients (86%) and CMCTs were prolonged in 493 patients (59%). An MEP study with TMS is a useful and non-invasive screening tool for an electrophysiological evaluation of myelopathy patients. Moreover, MEPs may be effective parameters in spinal pathology when considering details of the operative treatment. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. doi: 10.1016/j.spinee.2010.07.291

P16. Diagnostic Algorithm for Lumbar Foraminal Stenosis Using an Aggravating Activities Questionnaire Donald Corenman, MD, DC, Karen K. Briggs, MPH, MBA, Eric Strauch, PA, Kira C. Barclay, MPH; Steadman Philippon Research Institute, Vail, CO, USA BACKGROUND CONTEXT: Imaging is presently used to confirm a diagnosis of foraminal stenosis. However, imaging is costly and therefore not always used by primary care physicians to confirm or rule out foraminal stenosis. A diagnostic algorithm may assist physicians in patient evaluation and thereby reduce health care costs and improve patient care. PURPOSE: To establish a diagnostic algorithm for lumbar foraminal stenosis. STUDY DESIGN/SETTING: Cross sectional. PATIENT SAMPLE: 663 lumbar spine patients, 67 of which had foraminal stenosis. OUTCOME MEASURES: Diagnostic study. METHODS: During a 2 year period, all patients presenting to a private spine clinic with lumbar issues were asked to complete a questionnaire that included 56 questions about activities that aggravated their symptoms. After the patients were evaluated, diagnoses were made for each patient. The aggravating activities of those patients who were diagnosed with foraminal stenosis were compared to those who were not diagnosed with foraminal stenosis using Pearson’s chi-square test. RESULTS: Of the 56 questions asked, only 5 questions were significantly associated with the diagnosis of foraminal stenosis. These questions include aggravating symptoms when walking 30 minutes, standing 30 minutes, sleeping in the fetal position, and sleeping, and resolution of symptoms when bending to push a shopping cart (RS_SC). Sleeping and RS_SC had the highest positive likelihood ratio (See Table 1). If patients reported one or both of these symptoms, the sensitivity was 0.72, the specificity was 0.85, and the positive likelihood ratio was 4.8 [CI 3.8 to 5.8]. The area under the ROC curve was 0.785, indicating a good to excellent diagnostic performance of these two symptoms. (Figure 1). CONCLUSIONS: Questions about aggravating activities have predictive value in diagnosing foraminal stenosis. This study showed that, with the use of 2 questions which address an activity that resolves symptoms and one that aggravates symptoms, physicians can predict which patients are at a high likelihood of having foraminal stenosis. These 2 questions

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showed excellent diagnostic performance which may assist primary care physicians in the diagnosis and referral of patients with foraminal stenosis. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. doi: 10.1016/j.spinee.2010.07.292 P17. Complications Associated with Axial Lumbar Interbody Fusion Matthew McCullough, BS, Emily M. Lindley, PhD, Courtney Brown, MD, Evalina L. Burger, MD, Vikas V. Patel, MA, MD; University of Colorado Denver, Aurora, CO, USA BACKGROUND CONTEXT: Axial Lumbar Interbody Fusion (AxiaLIF) is a novel minimally invasive approach for fusion of the L5 vertebra to the sacrum. This technique uses the presacral space for percutaneous access to the anterior sacrum. AxiaLIF has the potential to decrease patient recovery time, length of hospital stay, and overall occurrence of surgical complication. It can be used alone or in combination with minimally invasive or traditional open fusion procedures. PURPOSE: The purpose of this study was to evaluate complications of the AxiaLIF procedure. STUDY DESIGN/SETTING: Retrospective chart review. PATIENT SAMPLE: Sixty-six patients treated with AxiaLIF surgery between October 2005 and June 2009 at the authors’ two institutions. OUTCOME MEASURES: Surgical complications. METHODS: Patients that underwent AxiLIF surgery at the two institutions were identified and their charts were reviewed, including operative reports and postoperative medical records, to determine what complications were encountered. RESULTS: A total of 66 patients underwent AxiaLIF surgery. Complications occurred in 14 (7 males and 7 females; mean age 56.4) of the 66 patients (21.2%). These complications included superficial infection (4.5%), deep infection (1.5%), pseudoarthrosis (4.5%), sacral fracture (1.5%), pseudoarthrosis and sacral fracture (3%), pelvic hematoma (3%), failure of wound closure (1.5%), and rectal perforation (1.5%). CONCLUSIONS: The complication rate associated with AxiaLIF in the present study was relatively low (21.2%) and was lower than previously published complication rates for transforaminal lumbar interbody fusion (33.6%) and anterior lumbar interbody fusion (38.3%). The most common complications were superficial infection and pseudoarthrosis. We had one case of rectal perforation that required exploratory laprotomy and a loop colonoscopy for repair of the perforation. It is important for surgeons to be aware of the potential for these complications. Many of these complications can likely be avoided with proper patient selection and operative planning. Pre-operative MRI, a detailed patient physical and history, adequate bowel preparation, improved access instrumentation, and the use of live fluoroscopy can all help to prevent complications with AxiaLIF surgery. FDA DEVICE/DRUG STATUS: This abstract does not discuss or include any applicable devices or drugs. doi: 10.1016/j.spinee.2010.07.293

P18. Kinematic Evaluation of the Adjacent Segments after Lumbar Instrumented Surgery Yuichiro Morishita, Hideki Ohta, MD, Yoshiyuki Matsumoto, MD, George Huang, MD, Tsubasa Sakai, MD, Yoshiharu Takemitsu, MD, Hirotaka Kida, MD, PhD; Oita Orthopedic Hospital, Oita, Japan BACKGROUND CONTEXT: Recently, several experiments have been devised to measure the positive effects of dynamic non-fusion stabilization techniques. It has been proposed that non-fusion motion preservation techniques may prevent accelerated adjacent segment degeneration because of the protective effect of the persisting segmental motion. However, biomechanical and kinematical effects on instrumented and adjacent segments are still a matter of discussion, and most of them evaluated lumbar

All referenced figures and tables will be available at the Annual Meeting and will be included with the post-meeting online content.