Percutaneous lumbar pedicle screw placement aided by computer-assisted fluoroscopy-based navigation: perioperative results of a prospective, comparative, multicenter study.

STUDY DESIGN: Institutional review board-approved, prospective, multicenter, comparative study. OBJECTIVE: To assess the accuracy and utility of a computer-assisted fluoroscopic navigation method for percutaneous placement of lumbar pedicle screws compared with conventional fluoroscopic placement. SUMMARY OF BACKGROUND DATA: Recent reports indicate that cortical breaches during percutaneous pedicle screw placement can exceed 15%. Computed tomography (CT)- and fluoroscopy-based navigation systems may facilitate increased placement accuracy with reduced radiation exposure and operative times. METHODS: Patients were alternately assigned to either the Guidance or Control group. The Guidance group underwent lumbar pedicle screw placement using the oblique visualization technique and computer-assisted fluoroscopic navigation. The Control group underwent lumbar pedicle screw placement per standard percutaneous technique aided by fluoroscopy alone. Baseline demographics, visual analog scale (VAS) pain scores, and American Spinal Injury Association scores were obtained preoperatively and in the immediate postoperative period. Fluoroscopy times and guidewire insertion times were recorded intraoperatively. All postoperative CT scans were reviewed by an independent spine surgeon to grade screw placement accuracy. RESULTS: Forty-two patients (210 screws) were assigned to the Guidance group and 34 patients (152 screws) were assigned to the Control group. Use of Guidance resulted in reduced average fluoroscopy usage per pedicle [6.6 sec (SD = 5.1) vs. 9.6 sec (SD 6.2), P < 0.001] and more expedient placement of guidewires per pedicle [3.65 min (SD = 2.31) vs. 4.43 min (SD = 2.56), P = 0.003]. The Guidance group experienced less than half of the breach rate of the Control group (3.0% vs. 7.2%, P = 0.055) and reduced breach magnitudes. None of the breaches resulted in a corresponding neurological deficit or required revision. All patient-reported outcomes were significantly improved after surgery and there were no significant differences in average postoperative VAS scores between treatment groups. CONCLUSION: Use of Guidance reduces fluoroscopy and insertion times with increased accuracy compared with conventional fluoroscopic methods of percutaneous pedicle screw insertion.

Thoracic pedicle subtraction osteotomy for fixed sagittal spinal deformity.

STUDY DESIGN.: A retrospective clinical study. OBJECTIVE.: To find the corrective capacity of a thoracic pedicle subtraction osteotomy (PSO), determine if segmental correction is dependent on level, and to compute the impact of thoracic PSO on regional and global spinal balance. SUMMARY OF BACKGROUND DATA.: PSO is a technique popularized in the lumbar spine primarily for the correction of fixed sagittal imbalance. Despite several studies describing the clinical and radiographic outcome of lumbar PSO, there is no study in literature reporting its application in the thoracic spine. METHODS.: We retrospectively analyzed patients with fixed thoracic kyphosis who underwent thoracic PSOs for sagittal realignment. Segmental pedicle screw instrumentation and intraoperative neurophysiologic monitoring was used in all patients. Data acquisition was performed by reviewing medical charts and radiographs to determine sagittal correction (segmental/regional/global) and complications. Clinical outcome using the Scoliosis Research Society-22 (SRS-22) instrument was determined by interview. RESULTS.: A total of 25 thoracic PSOs were performed (mean: 1.7 PSOs/patient, range: 1-3) in 15 patients (9 M/6 F). The study population had an average age of 56 years (range, 36-81 years) and was followed up after surgery for a mean of 3.5 years (range, 24-75 months). The osteotomies were carried out in the proximal thoracic spine (T2-T4, n = 6), midthoracic spine (T5-T8, n = 12), and distal thoracic spine (T9-T12, n = 7). Mean correction at the PSO for all 25 levels was 16.3 degrees +/- 9.6 degrees . Stratified by region of the spine, thoracic PSO correction was as follows: T2-T4 = 10.7 degrees +/- 15.8 degrees , T5-T8 = 14.7 degrees +/- 4.6 degrees , and T9-T12 = 23.9 degrees +/- 4.1 degrees . Mean thoracic kyphosis (T2-T12 Cobb angle) was improved from 75.7 degrees +/- 30.9 degrees to 54.3 degrees +/- 21.4 degrees resulting in a significant regional sagittal correction of 21.4 degrees +/- 13.7 degrees (P < 0.005). Global sagittal balance was improved from 106.1 +/- 56.6 to 38.8 +/- 37.0 mm yielding a mean correction of 67.3 +/- 54.7 mm (P < 0.005). One patient, in whom there was segmental translation during osteotomy closure, had a decline in intraoperative somatosensory-evoked potentials. No patient sustained a temporary or permanent neurologic deficit after surgery. The mean SRS-22 Questionnaire score at final follow-up was 82.4 +/- 10.2. CONCLUSION.: Thoracic PSO can be performed safely. Segmental sagittal correction appears to vary based on the region of the thoracic spine the PSO is performed. The distal thoracic segments, which more closely resemble lumbar segments in morphology, rendered the greatest sagittal correction after PSO, approximately 24 degrees . There was no case of neurologic injury associated with thoracic PSO, and clinical outcomes according to the SRS-22 instrument were generally favorable.

Surgical management of superficial siderosis.

BACKGROUND CONTEXT: Superficial siderosis is a rare condition resulting from the presence of chronic bleeding into the subarachnoid space usually causing gait instability and deafness. The surgical management of superficial siderosis depends on localizing the source of hemorrhage. PURPOSE: The surgical treatment of this rare condition has not been well described in the literature. We present a case illustrating the surgical treatment for superficial siderosis. STUDY DESIGN: Case report. PATIENT SAMPLE: The authors describe the case report of a 70-year-old gentleman with gait instability and deafness found to have an abnormal communication between the spinal epidural venous plexus and the subarachnoid space. METHODS: The source of hemorrhage into the subarachnoid space was identified to be a fistula in the ventral thoracic dural. A costotransversectomy approach was undertaken at the T4-T5 level to expose the fistula. The abnormal communication was patched and sealed. RESULTS: The patient's symptoms remained stable on follow-up at 15 months with no worsening of his symptoms. CONCLUSIONS: Superficial siderosis is a neurologic disorder that arises from chronic hemosiderin deposition into the subarachnoid space. The progressive nature of the disease can be halted if a source of hemorrhage can be found and treated surgically.

A novel mathematical model of the sagittal spine: application to pedicle subtraction osteotomy for correction of fixed sagittal deformity.

BACKGROUND CONTEXT: The C7 plumb line method oversimplifies the true complexity of the spine. In a previous study, we mathematically modeled the normal spine using the spline function, enabling quantification of previously undescribed measurements such as area under the curve (AUC) and average sagittal position. The spine in fixed sagittal imbalance and the results of surgical correction have not been studied in a similar manner. PURPOSE: To quantitatively evaluate changes in spinal conformation in patients who underwent pedicle subtraction osteotomy (PSO) using measures derived from the spline model and to correlate these changes with functional outcome. STUDY DESIGN: Application of a mathematical model to a cohort of patients who underwent deformity surgery. PATIENT SAMPLE: Thirty-four consecutive patients with fixed sagittal imbalance who underwent PSO from 2001 to 2003. OUTCOME MEASURES: Preoperative and postoperative 22-item Scoliosis Research Society (SRS-22) Outcomes Questionnaire scores were used for functional assessment. METHODS: Radiographs of the 34 patients who underwent thoracic or lumbar PSO with at least 2 years of follow-up were examined at three time points. The posterosuperior aspect of each vertebral body was chosen as a representative point for the spinal sagittal curve. A cubic spline function was derived from these points. From this function, the AUCs and average sagittal positions of the thoracic, lumbar, and thoracolumbar segments were calculated. RESULTS: The average sagittal position does not overlap the C7 plumb line in deformity patients, but is a much more stable measure. In the lumbar PSO cohort, the lumbar AUC and average sagittal position were not significantly different among normal, preoperative, and postoperative groups. The thoracic and thoracolumbar AUCs and average sagittal positions were dramatically more positive in the preoperative cohort compared with normals; these values significantly decreased toward neutrality after lumbar PSO, but remained abnormal. In the thoracic PSO cohort, the lumbar, thoracic, and thoracolumbar AUCs and average sagittal positions were not significantly different among normal, preoperative, and postoperative groups. The changes in thoracolumbar AUC and average sagittal position were better predictors of the SRS-22 total score than the change in C7 plumb line. CONCLUSIONS: The average sagittal position more comprehensively captures the nuances of a nonlinear spinal curve. Subcurve analysis enabled by the spline model is particularly helpful in assessing deformity and surgical correction on a segmental level. Increased sensitivity to the nuances of the spinal curve in this model results in superior correlation with clinical outcomes when compared with the C7 plumb line. We feel that a critical examination of the spinal curve will lead to improved understanding of deformity and planning for an optimal correction.

Unruptured arteriovenous malformation in a patient presenting with obstructive hydrocephalus. Case report and review of the literature.

The authors report on a patient harboring an unruptured cortical arteriovenous malformation (AVM), who had presented with obstructive hydrocephalus due to compression of the cerebral aqueduct by a large venous varix. Although patients with ruptured AVMs are known to either present with or later suffer from obstructive hydrocephalus, those with unruptured AVMs who present in this manner are quite rare. Moreover, hydrocephalus caused by a venous varix draining an AVM, to our knowledge, has never been previously reported in the literature. This report serves to illustrate two primary points, namely, that tortuous venous varices draining AVMs can result in obstructive hydrocephalus and that this unusual circumstance can be fostered in the setting of venous outflow obstruction.

A novel mathematical model of the sagittal spine.

STUDY DESIGN: Development of a mathematical model with application to a cohort of healthy volunteers. OBJECTIVES: To derive a smooth mathematical function representing the sagittal spinal curve from individual vertebral elements. To generate normative data using this model. SUMMARY OF BACKGROUND DATA: Current concepts of spinal sagittal balance center on the C7 plumb line. While elegant in its ease of use, this method oversimplifies the true complexity of the spine. If the spinal curve could be expressed as a smooth mathematical function, the ability to analyze sagittal balance would be greatly enhanced. METHODS: Lateral full-length radiographs of 18 normal volunteers were examined. The posterosuperior aspect of each vertebral body was chosen as a representative point for the spinal sagittal curve. A cubic spline function was derived from these points. From this function, the area under the curve (AUC) and average sagittal positions of the thoracic, lumbar, and thoracolumbar segments were calculated. RESULTS: Assuming an average vertebral column height of 60 cm with anterior being positive, the average position of the posterosuperior aspect of C7 relative to S1 was -2.8 cm (+/-3.0). The average thoracolumbar AUC was -161 cm2 (+/-83). The average lumbar and thoracic AUCs were 0 cm2 (+/-17) and -157 cm2 (+/-68), respectively. The average sagittal position over the thoracolumbar curve was -3.3 cm (+/-1.7). The average sagittal positions of the lumbar and thoracic subcurves were 0.1 cm (+/-1.1) and -5.1 cm (+/-2.2), respectively. Intraobserver and interobserver reliabilities were excellent. CONCLUSIONS: A mathematical model of the sagittal spine that retains the spine's segmental nuances was derived using cubic spline interpolation. The average sagittal position of the thoracolumbar spine, a calculation based on the AUC, is a less variable measure of sagittal balance than the C7 plumb line. The model and normative data generated from it will allow more insightful investigations of spinal deformity and more quantitative evaluations of corrective outcomes.

Endovascular treatment strategies for cerebral vasospasm.

Cerebral vasospasm is a significant cause of morbidity and mortality in patients who have sustained a subarachnoid hemorrhage from aneurysm rupture. Symptomatic cerebral vasospasm is also a strong predictor of poor clinical outcome and has thus drawn a great deal of interest from cerebrovascular surgeons. Although medical management is the cornerstone of treatment for this condition, endovascular intervention may be warranted for those in whom this treatment fails and in whom symptomatic vasospasm subsequently develops. The rapid advancements in endovascular techniques and pharmacological agents used to combat this pathological state continue to offer promise in broadening the available treatment armamentarium. In this article the authors discuss the rationale and basis for using the various endovascular options for the treatment of cerebral vasospasm, and they also discuss the limitations, complications, and efficacy of these treatment strategies in regard to neurological condition and outcome.

A method for calculating the exact angle required during pedicle subtraction osteotomy for fixed sagittal deformity: comparison with the trigonometric method.

OBJECTIVE: Pedicle subtraction osteotomy (PSO) has emerged as a powerful procedure for correcting fixed sagittal deformity. There has only been one attempt to quantify the magnitude of correction needed to restore sagittal balance; the trigonometric method for calculating the desired PSO angle is an approximation. We propose a method for calculating the exact angle required for PSO and explore how this angle differs from that obtained via the trigonometric method in illustrative cases. METHODS: We conducted a mathematical analysis of the spine with application in illustrative cases. The trigonometric method calculates the necessary angular correction at the axial level of the PSO, but along the sacral vertical line. However, the angular measurement should take place at the true axis of rotation, the apex of the PSO. Measurements were taken from full-length standing x-rays, and both methods were explored. RESULTS: The trigonometric method for calculating PSO angle is an exact measurement only if the apex of the PSO site lies on the sacral vertical line. As the apex of the PSO site moves anterior to that line, the trigonometric approximation underestimates the actual angle. As the apex of the PSO moves posterior to that line, the trigonometric approximation overestimates the actual angle. CONCLUSION: The trigonometric method for calculating the PSO angle required for surgical deformity correction is an approximation, but its validity in clinical practice was confirmed by this study. The exact angle is obtained by a method centered on the apex of the PSO site. Although the difference between these angles is small, it is an important conceptual point for spine surgeons. Measurement of the exact angle is easily performed and should replace the trigonometric method for calculating the required PSO angle when standard digital measurement tools are available.

Clinical and radiographic outcomes of thoracic and lumbar pedicle subtraction osteotomy for fixed sagittal imbalance.

OBJECT: The authors conducted a study to evaluate the radiographically documented and functional outcomes obtained in patients who underwent pedicle subtraction osteotomy (PSO). They also compared outcomes after classification of cases into thoracic and lumbar PSO subgroups. METHODS: The authors analyzed data obtained in 35 consecutive PSO-treated patients with sagittal imbalance. One surgeon performed all surgeries. The minimal follow-up period was 2 years. Events during the perioperative course and complications were noted. Standing long-film radiographs of the spine were obtained and measurements were made preoperatively, immediately postoperatively, and at most recent follow-up examination. The modified Prolo Scale and the 22-item Scoliosis Research Society (SRS-22) Outcomes Questionnaire were administered. Early complications after PSO included neurological injury, wound-related problems, and nosocomial infections. Late complications were limited to pseudarthrosis and attendant instrumentation failure. Early and late complication rates ranged from 10 to 30% for both thoracic and lumbar PSO cohorts. Lumbar PSO was associated with improvements in local, segmental, and global measures of sagittal balance, whereas thoracic PSO was only associated with local improvement. Most patients rated their functional status as fair to good according to the modified Prolo Scale and reported, according to the SRS-22 Outcomes Questionnaire, that they were satisfied with the overall treatment of their back condition. CONCLUSIONS: The ability to perform a PSO at both lumbar and thoracic levels is a powerful asset for the spine surgeon treating spinal deformity. In the present study radiographic and clinical outcomes were superior when PSO was used to treat lumbar deformity rather than thoracic deformity because of several anatomical and technical obstacles that hindered the thoracic procedure. Nevertheless, the thoracic PSO proved a useful addition with which to produce regional improvement in sagittal balance for patients with a fixed thoracic kyphosis.

Cerebral cavernous malformations: clinical insights from genetic studies.

Familial disease is responsible for one third to one half of cerebral cavernous malformation (CCM) cases presenting to clinical attention. Much has been learned in the past decade about the genetics of these cases, which are all inherited in an autosomal dominant pattern, at three known chromosome loci. Unique features of inherited CCMs in Hispanic-Americans of Mexican descent have been described. The respective genes for each locus have been identified and preliminary observations on disease pathways and mechanisms are coming to light, including possible explanations for selectivity of neural milieu and relationships to endothelial layer abnormalities. Mechanisms of lesion genesis in cases of genetic predisposition are being investigated, with evidence to support a two-hit model emerging from somatic mutation screening of the lesions themselves and from lesion formation in transgenic murine models of the disease. Other information on potential inflammatory factors has emerged from differential gene expression studies. Unique phenotypic features of solitary versus familial cases have emerged: different associations with venous developmental anomaly and the exceptionally high penetrance rates that are found in inherited cases when high-sensitivity screening is performed with gradient echo magnetic resonance imaging. This information has changed the landscape of screening and counseling for patients and their families, and promises to lead to the development of new tools for predicting, explaining, and modifying disease behavior.

Contrast-enhanced MR angiography of the carotid and vertebrobasilar circulations.

BACKGROUND AND PURPOSE: Contrast-enhanced MR angiography (CE MRA) is a proven diagnostic tool in evaluation of the carotid arteries; however, few studies have addressed its accuracy in the vertebrobasilar system. The purpose of this study was to assess the sensitivity and specificity of CE MRA compared with digital subtraction angiography (DSA) for detection of vertebrobasilar disease. METHODS: Forty patients with suspected atherosclerotic disease of the carotid and vertebrobasilar circulations underwent CE MRA on a 1.5 T MR imaging scanner by use of a coronal 3D gradient-echo pulse sequence after intravenous injection of gadolinium diethylene triamine penta-acetic acid. All patients had correlative DSA within a 1-month period. CE MRA images were randomized and then independently assessed by 2 observers who were blinded to the DSA results. DSA examinations were analyzed in a similar manner. Each observer was asked to report the presence or absence of clinically significant stenosis (>50%), occlusion, fistula, aneurysm, and dissection. The MRA findings were then correlated with DSA. RESULTS: The sensitivity and specificity of MRA for detection of disease in the entire carotid and vertebrobasilar systems were 90% and 97%, respectively; for the carotid system alone, the sensitivity and specificity were 94% and 97%, respectively; and for the vertebrobasilar system they were 88% and 98% respectively. The overall interobserver reliability was 98% (kappa = 0.92). CONCLUSION: CE MRA is accurate at detecting disease not only in the carotid vessels, but also in the vertebrobasilar circulation, and has the potential to provide a comprehensive and noninvasive evaluation of the head and neck arteries in a single study.