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Ryan M. Kretzer, Christopher Chaput, Daniel M. Sciubba, Ira M. Garonzik, George I. Jallo, Paul C. McAfee, Bryan W. Cunningham and P. Justin Tortolani

Object

The objective of this study was to establish normative data for thoracic pedicle anatomy in the US adult population. To this end, CT scans chosen at random from an adult database were evaluated to determine the ideal pedicle screw (PS) length, diameter, trajectory, and starting point in the thoracic spine. The role of patient sex and side of screw placement were also assessed. The authors postulated that this information would be of value in guiding safe implant size and placement for surgeons in training.

Methods

One hundred patients (50 males and 50 females) were selected via retrospective review of a hospital trauma registry database over a 6-month period. Patients included in the study were older than 18 years of age, had axial bone-window CT images of the thoracic spine, and had no evidence of spinal trauma. For each pedicle, the pedicle width, pedicle-rib width, estimated screw length, trajectory, and ideal entry point were measured using eFilm Lite software. Statistical analysis was performed using the Student t-test.

Results

The shortest mean estimated PS length was at T-1 (33.9 ± 3.3 mm), and the longest was at T-9 (44.9 ± 4.4 mm). Pedicle screw length was significantly affected by patient sex; men could accommodate a PS from T1–12 a mean of 4.0 ± 1.0 mm longer than in women (p < 0.001). Pedicle width showed marked variation by spinal level, with T-4 (4.4 ± 1.1 mm) having the narrowest width and T-12 (8.3 ± 1.7 mm) having the widest. Pedicle width had an obvious affect on potential screw diameter; 65% of patients had a least 1 pedicle at T-4 that was < 5 mm in diameter and therefore would not accept a 4.0-mm screw with 1.0 mm of clearance, as compared with only 2% of patients with a similar status at T-12. Sex variation was also apparent, as thoracic pedicles from T-1 to T-12 were a mean of 1.4 ± 0.2 mm wider in men than in women (p < 0.001). The PS trajectory in the axial plane was measured, showing a marked decrease from T-1 to T-4, stabilization from T-5 to T-10, followed by a decrease at T11–12. When screw trajectory was stratified by side of placement, a mean of 1.7° ± 0.5° of increased medialization was required for ideal pedicle cannulation from T-3 to T-12 on the left as compared with the right side, presumably because of developmental changes in the vertebral body caused by the aorta (p < 0.05 for T3–12, except for T-5, where p = 0.051). The junction of the superior articular process, lamina, and the superior ridge of the transverse process was shown to be a conserved surface landmark for PS placement.

Conclusions

Preoperative CT evaluation is important in choosing PS length, diameter, trajectory, and entry point due to variation based on spinal level, patient sex, and side of placement. These data are valuable for resident and fellow training to guide the safe use of thoracic PSs.

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Risheng Xu, Matthew J. McGirt, Edward G. Sutter, Daniel M. Sciubba, Jean-Paul Wolinsky, Timothy F. Witham, Ziya L. Gokaslan and Ali Bydon

Object

The aim of this study was to conduct the first in vitro biomechanical comparison of immediate and postcyclical rigidities of C-7 lateral mass versus C-7 pedicle screws in posterior C4–7 constructs.

Methods

Ten human cadaveric spines were treated with C4–6 lateral mass screw and C-7 lateral mass (5 specimens) versus pedicle (5 specimens) screw fixation. Spines were potted in polymethylmethacrylate bone cement and placed on a materials testing machine. Rotation about the axis of bending was measured using passive retroreflective markers and infrared motion capture cameras. The motion of C-4 relative to C-7 in flexion-extension and lateral bending was assessed uninstrumented, immediately after instrumentation, and following 40,000 cycles of 4 Nm of flexion-extension and lateral bending moments at 1 Hz. The effect of instrumentation and cyclical loading on rotational motion across C4–7 was analyzed for significance.

Results

Preinstrumented spines for the 2 cohorts were comparable in bone mineral density and range of motion in both flexion-extension (p = 0.33) and lateral bending (p = 0.16). Lateral mass and pedicle screw constructs significantly reduced motion during flexion-extension (11.3°–0.26° for lateral mass screws, p = 0.002; 10.51°–0.30° for pedicle screws, p = 0.008) and lateral bending (7.38°–0.27° for lateral mass screws, p = 0.003; 11.65°–0.49° for pedicle screws, p = 0.03). After cyclical loading in both cohorts, rotational motion over C4–7 was increased during flexion-extension (0.26°–0.68° for lateral mass screws; 0.30°–1.31° for pedicle screws) and lateral bending (0.27°–0.39° and 0.49°–0.80°, respectively), although the increase was not statistically significant (p > 0.05). There was no statistical difference in postcyclical flexion-extension (p = 0.20) and lateral bending (0.10) between lateral mass and pedicle screws.

Conclusions

Both C-7 lateral mass and C-7 pedicle screws allow equally rigid fixation of subaxial lateral mass constructs ending at C-7. Immediately and within a simulated 6-week postfixation period, C-7 lateral mass screws may be as effective as C-7 pedicle screws in biomechanically stabilizing long subaxial lateral mass constructs.

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Daniel M. Sciubba, E. Clif Burdette, Jennifer J. Cheng, William A. Pennant, Joseph C. Noggle, Rory J. Petteys, Christopher Alix, Chris J. Diederich, Gabor Fichtinger, Ziya L. Gokaslan and Kieran P. Murphy

Object

Radiofrequency ablation (RFA) has proven to be effective for treatment of malignant and benign tumors in numerous anatomical sites outside the spine. The major challenge of using RFA for spinal tumors is difficulty protecting the spinal cord and nerves from damage. However, conforming ultrasound energy to match the exact anatomy of the tumor may provide successful ablation in such sensitive locations. In a rabbit model of vertebral body tumor, the authors have successfully ablated tumors using an acoustic ablator placed percutaneously via computed tomography fluoroscopic (CTF) guidance.

Methods

Using CTF guidance, 12 adult male New Zealand White rabbits were injected with VX2 carcinoma cells in the lowest lumbar vertebral body. At 21 days, a bone biopsy needle was placed into the geographical center of the lesion, down which an acoustic ablator was inserted. Three multisensor thermocouple arrays were placed around the lesion to provide measurement of tissue temperature during ablation, at thermal doses ranging from 100 to 1,000,000 TEM (thermal equivalent minutes at 43°C), and tumor volumes were given a tumoricidal dose of acoustic energy. Animals were monitored for 24 hours and then sacrificed. Pathological specimens were obtained to determine the extent of tumor death and surrounding tissue damage. Measured temperature distributions were used to reconstruct volumetric doses of energy delivered to tumor tissue, and such data were correlated with pathological findings.

Results

All rabbits were successfully implanted with VX2 cells, leading to a grossly apparent spinal and paraspinal tissue mass. The CTF guidance provided accurate placement of the acoustic ablator in all tumors, as corroborated through gross and microscopic histology. Significant tumor death was noted in all specimens without collateral damage to nearby nerve tissue. Tissue destruction just beyond the margin of the tumor was noted in some but not all specimens. No neurological deficits occurred in response to ablation. Reconstruction of measured temperature data allowed accurate assessment of volumetric dose delivered to tissues.

Conclusions

Using a rabbit intravertebral tumor model, the authors have successfully delivered tumoricidal doses of acoustic energy via a therapeutic ultrasound ablation probe placed percutaneously with CTF guidance. The authors have thus established the first technical and preclinical feasibility study of controlled ultrasound ablation of spinal tumors in vivo.

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Ryan M. Kretzer, Nianbin Hu, Hidemasa Umekoji, Daniel M. Sciubba, George I. Jallo, Paul C. McAfee, P. Justin Tortolani and Bryan W. Cunningham

Object

Thoracic pedicle screw instrumentation is often indicated in the treatment of trauma, deformity, degenerative disease, and oncological processes. Although classic teaching for cervical spine constructs is to bridge the cervicothoracic junction (CTJ) when instrumenting in the lower cervical region, the indications for extending thoracic constructs into the cervical spine remain unclear. The goal of this study was to determine the role of ligamentous and facet capsule (FC) structures at the CTJ as they relate to stability above thoracic pedicle screw constructs.

Methods

A 6-degree-of-freedom spine simulator was used to test multidirectional range of motion (ROM) in 8 human cadaveric specimens at the C7–T1 segment. Flexion-extension, lateral bending, and axial rotation at the CTJ were tested in the intact condition, followed by T1–6 pedicle screw fixation to create a long lever arm inferior to the C7–T1 level. Multidirectional flexibility testing of the T1–6 pedicle screw construct was then sequentially performed after sectioning the C7–T1 supraspinous ligament/interspinous ligament (SSL/ISL) complex, followed by unilateral and bilateral FC disruption at C7–T1. Finally, each specimen was reconstructed using C5–T6 instrumented fixation and ROM testing at the CTJ performed as previously described.

Results

Whereas the application of a long-segment thoracic construct stopping at T-1 did not significantly increase flexion-extension peak total ROM at the supra-adjacent level, sectioning the SSL/ISL significantly increased flexibility at C7–T1, producing 35% more motion than in the intact condition (p < 0.05). Subsequent FC sectioning had little additional effect on ROM in flexion-extension. Surprisingly, the application of thoracic instrumentation had a stabilizing effect on the supra-adjacent C7–T1 segment in axial rotation, leading to a decrease in peak total ROM to 83% of the intact condition (p < 0.05). This is presumably due to interaction between the T-1 screw heads and titanium rods with the C7–T1 facet joints, thereby limiting axial rotation. Incremental destabilization served only to restore peak total ROM near the intact condition for this loading mode. In lateral bending, the application of thoracic instrumentation stopping at T-1, as well as SSL/ISL and FC disruption, demonstrated trends toward increased supraadjacent ROM; however, these trends did not reach statistical significance (p > 0.05).

Conclusions

When stopping thoracic constructs at T-1, care should be taken to preserve the SSL/ISL complex to avoid destabilization of the supra-adjacent CTJ, which may manifest clinically as proximal-junction kyphosis. In an analogous fashion, if a T-1 laminectomy is required for neural decompression or surgical access, consideration should be given to extending instrumentation into the cervical spine. Facet capsule disruption, as might be encountered during T-1 pedicle screw placement, may not be an acutely destabilizing event, due to the interaction of the C7–T1 facet joints with T-1 instrumentation.

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Oral Presentations

2010 AANS Annual Meeting Philadelphia, Pennsylvania May 1–5, 2010

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Daniel M. Sciubba, Rory J. Petteys, Mark B. Dekutoski, Charles G. Fisher, Michael G. Fehlings, Stephen L. Ondra, Laurence D. Rhines and Ziya L. Gokaslan

With continued growth of the elderly population and improvements in cancer therapies, the number of patients with symptomatic spinal metastases is likely to increase, and this is a condition that commonly leads to debilitating neurological dysfunction and pain. Advancements in surgical techniques of resection and spinal reconstruction, improvements in clinical outcomes following various treatment modalities, generally increased overall survival in patients with metastatic spine disease, and a recent randomized trial by Patchell and colleagues demonstrating the superiority of a combined surgical/radiotherapeutic approach over a radiotherapy-only strategy have led many to suggest increasingly aggressive interventions for patients with such lesions. Optimal management of spinal metastases encompasses numerous medical specialties, including neurosurgery, orthopedic surgery, medical and radiation oncology, radiology, and rehabilitation medicine. In this review, the clinical presentation, diagnosis, and management of spinal metastatic disease are discussed. Ultimately, the goal of treatment in patients with spinal metastases remains palliative, and clinical judgment is required to select the appropriate patients for surgical intervention.

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Ryan M. Kretzer, Christopher Chaput, Daniel M. Sciubba, Ira M. Garonzik, George I. Jallo, Paul C. McAfee, Bryan W. Cunningham and P. Justin Tortolani

Object

Translaminar screws (TLSs) offer an alternative to pedicle screw (PS) fixation in the upper thoracic spine. Although cadaveric studies have described the anatomy of the laminae and pedicles at T1–2, CT imaging is the modality of choice for presurgical planning. In this study, the goal was to determine the diameter, maximal screw length, and optimal screw trajectory for TLS placement at T1–2, and to compare this information to PS placement in the upper thoracic spine as determined by CT evaluation.

Methods

One hundred patients (50 men and 50 women), whose average age was 41.7 ± 19.6 years, were selected by retrospective review of a trauma registry database over a 6-month period. Patients were included in the study if they were over the age of 18, had standardized axial bone-window CT imaging at T1–2, and had no evidence of spinal trauma. For each lamina and pedicle, width (outer cortical and cancellous), maximal screw length, and optimal screw trajectory were measured using eFilm Lite software. Statistical analysis was performed using the Student t-test.

Results

The T-1 lamina was estimated to accommodate, on average, a 5.8-mm longer screw than the T-2 lamina (p < 0.001). At T-1, the maximal TLS length was similar to PS length (TLS: 33.4 ± 3.6 mm, PS: 33.9 ± 3.3 mm [p = 0.148]), whereas at T-2, the maximal PS length was significantly greater than the TLS length (TLS: 27.6 ± 3.1 mm, PS: 35.3 ± 3.5 mm [p < 0.001]). When the lamina outer cortical and cancellous width was compared between T-1 and T-2, the lamina at T-2 was, on average, 0.3 mm wider than at T-1 (p = 0.007 and p = 0.003, respectively). In comparison with the corresponding pedicle, the mean outer cortical pedicle width at T-1 was wider than the lamina by an average of 1.0 mm (lamina: 6.6 ± 1.1 mm, pedicle: 7.6 ± 1.3 mm [p < 0.001]). At T-2, however, outer cortical lamina width was wider than the corresponding pedicle by an average of 0.6 mm (lamina: 6.9 ± 1.1 mm, pedicle: 6.3 ± 1.2 mm [p < 0.001]). At T-1, 97.5% of laminae measured could accept a 4.0-mm screw with 1.0 mm of clearance, compared with 99.5% of T-1 pedicles; whereas at T-2, 99% of laminae met this requirement, compared with 94.5% of pedicles. The ideal screw trajectory was also measured (T-1: 49.2 ± 3.7° for TLS and 32.8 ± 3.8° for PS; T-2: 51.1 ± 3.5° for TLS and 20.5 ± 4.4° for PS).

Conclusions

Based on CT evaluation, there are no anatomical limitations to the placement of TLSs compared with PSs at T1–2. Differences were noted, however, in lamina length and width between T-1 and T-2 that must be considered when placing TLS at these levels.

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Geoffrey P. Colby, Alexander L. Coon, Daniel M. Sciubba, Ali Bydon, Philippe Gailloud and Rafael J. Tamargo

Spinal dural arteriovenous fistulas (DAVFs) are the most common type of spinal arteriovenous malformation and are an important, underdiagnosed cause of progressive myelopathy and morbidity in patients with spine disorders. Successful microsurgical management of these lesions is dependent on the surgeon's ability to identify vessels of the fistula and to confirm its successful obliteration postintervention. Indocyanine green (ICG) fluorescent angiography is an emerging tool for delineating intraoperative vascular anatomy, and it has significant potential utility in the treatment of vascular disease in the spine.

The authors present the case of a 76-year-old man with progressive and debilitating bilateral lower-extremity weakness and numbness on exertion, in whom a left T-8 spinal DAVF was diagnosed based on results of conventional spinal angiography. Unfavorable anatomy based on angiographic findings precluded endovascular embolization of the fistula, and the patient subsequently underwent T7–9 bilateral laminectomies for microsurgical clip occlusion. Intraoperative ICG fluorescent angiography was used before clip placement to identify the arterialized veins of the fistula, and after clip placement to confirm obliteration of the fistulous connection and restoration of normal blood flow.

Intraoperative ICG angiography serves an important role in the microsurgical treatment of DAVF. It can be used to map the anatomy of the fistula in real time during surgery and to verify fistula obliteration rapidly after clip placement. This report adds to the growing body of literature demonstrating the importance of ICG angiography in vascular neurosurgery of the spine.

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Daniel M. Sciubba, Rory J. Petteys, Sophia F. Shakur, Ziya L. Gokaslan, Edward F. McCarthy, Michael T. Collins, Matthew J. McGirt, Patrick C. Hsieh, Clarke S. Nelson and Jean-Paul Wolinsky

En bloc spondylectomy represents a radical resection of a spinal segment most often reserved for patients presenting with a primary extradural spine tumor or a solitary metastasis in the setting of an indolent, well-controlled systemic malignancy. The authors report a case in which en bloc spondylectomy was conducted to control a metabolically active spine tumor. A 56-year-old woman, who suffered from severe tumor-induced osteomalacia, was found to have a fibroblast growth factor-23–secreting phosphaturic mesenchymal tumor in the T-8 vertebral body. En bloc resection was conducted, leading to resolution of her tumor-induced osteomalacia. This case suggests that radical spondylectomy may be beneficial in the management of metabolically or endocrinologically active tumors of the spine.

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Giannina L. Garcés-Ambrossi, Matthew J. McGirt, Vivek A. Mehta, Daniel M. Sciubba, Timothy F. Witham, Ali Bydon, Jean-Paul Wolinksy, George I. Jallo and Ziya L. Gokaslan

Object

With the introduction of electrophysiological spinal cord monitoring, surgeons have been able to perform radical resection of intramedullary spinal cord tumors (IMSCTs). However, factors associated with tumor resectability, tumor recurrence, and long-term neurological outcome are poorly understood.

Methods

The authors retrospectively reviewed 101 consecutive cases of IMSCT resection in adults and children at a single institution. Neurological function and MR images were evaluated preoperatively, at discharge, 1 month after surgery, and every 6 months thereafter. Factors associated with gross-total resection (GTR), progression-free survival (PFS), and long-term neurological improvement were assessed using multivariate regression analysis.

Results

The mean age of the patients was 41 ± 18 years and 17 (17%) of the patients were pediatric. Pathological type included ependymoma in 51 cases, hemangioblastoma in 15, pilocytic astrocytoma in 16, WHO Grade II astrocytoma in 10, and malignant astrocytoma in 9. A GTR was achieved in 60 cases (59%). Independent of histological tumor type, an intraoperatively identifiable tumor plane (OR 25.3, p < 0.0001) and decreasing tumor size (OR 1.2, p = 0.05) were associated with GTR. Thirty-four patients (34%) experienced acute neurological decline after surgery (associated with increasing age [OR 1.04, p = 0.02] and with intraoperative change in motor evoked potentials [OR 7.4, p = 0.003]); in 14 (41%) of these patients the change returned to preoperative baseline within 1 month. In 31 patients (31%) tumor progression developed by last follow-up (mean 19 months). Tumor histology (p < 0.0001) and the presence of an intraoperatively identified tumor plane (hazard ratio [HR] 0.44, p = 0.027) correlated with improved PFS. A GTR resulted in improved PFS for hemangioblastoma (HR 0.004, p = 0.04) and ependymoma (HR 0.2, p = 0.02), but not astrocytoma. Fifty-five patients (55%) maintained overall neurological improvement by last follow-up. The presence of an identifiable tumor plane (HR 3.1, p = 0.0004) and improvement in neurological symptoms before discharge (HR 2.3, p = 0.004) were associated with overall neurological improvement by last follow-up (mean 19 months).

Conclusions

Gross-total resection can be safely achieved in the vast majority of IMSCTs when an intraoperative plane is identified, independent of pathological type. The incidence of acute perioperative neurological decline increases with patient age but will improve to baseline in nearly half of patients within 1 month. Long-term improvement in motor, sensory, and bladder dysfunction may be achieved in a slight majority of patients and occurs more frequently in patients in whom a surgical plane can be identified. A GTR should be attempted for ependymoma and hemangioblastoma, but it may not affect PFS for astrocytoma. For all tumors, the intraoperative finding of a clear tumor plane of resection carries positive prognostic significance across all pathological types.