Anubhav G. Amin

Accuracy of Free-Hand Pedicle Screws in the Thoracic and Lumbar Spine: Analysis of 6816 Consecutive Screws

BACKGROUND:Pedicle screws are used to stabilize all 3 columns of the spine, but can be technically demanding to place. Although intraoperative fluoroscopy and stereotactic-guided techniques slightly increase placement accuracy, they are also associated with increased radiation exposure to patient and surgeon as well as increased operative time. OBJECTIVE:To describe and critically evaluate our 7-year institutional experience with placement of pedicle screws in the thoracic and lumbar spine using a free-hand technique. METHODS:We retrospectively reviewed records of all patients undergoing free-hand pedicle screw placement without fluoroscopy in the thoracic or lumbar spine between June 2002 and June 2009. Incidence and extent of cortical breach by misplaced pedicle screw was determined by review of postoperative computed tomography scans. We defined breach as more than 25% of the screw diameter residing outside of the pedicle or vertebral body cortex. RESULTS:A total of 964 patients received 6816 free-hand placed pedicle screws in the thoracic or lumbar spine. Indications for hardware placement were degenerative/deformity disease (51.2%), spondylolisthesis (23.7%), tumor (22.7%), trauma (11.3%), infection (7.6%), and congenital (0.9%). A total of 115 screws (1.7%) were identified as breaching the pedicle in 87 patients (9.0%). Breach occurred more frequently in the thoracic than the lumbar spine (2.5% and 0.9%, respectively; P < .0001) and was more often lateral (61.3%) than medial (32.8%) or superior (2.5%). T4 (4.1%) and T6 (4.0%) experienced the highest breach rate, whereas L5 and S1 had the lowest breach rate. Eight patients (0.8%) underwent revision surgery to correct malpositioned screws. CONCLUSION:Free-hand pedicle screw placement based on external anatomy alone can be performed with acceptable safety and accuracy and allows avoidance of radiation exposure encountered in fluoroscopic techniques. Image-guided assistance may be most valuable when placing screws between T4 and T6, where breach rates are highest.

Implications of spinopelvic alignment for the spine surgeon.

The relation of the pelvis to the spine has previously been overlooked as a contributor to sagittal balance. However, it is now recognized that spinopelvic alignment is important to maintain an energy-efficient posture in normal and disease states. The pelvis is characterized by an important anatomic landmark, the pelvic incidence (PI). The PI does not change after adolescence, and it directly influences pelvic alignment, including the parameters of pelvic tilt (PT) and sacral slope (SS) (PI = PT 1 SS), overall sagittal spinal balance, and lumbar lordosis. In the setting of an elevated PI, the spineadapts with increased lumbar lordosis. To prevent or limit sagittal imbalance, the spine may also compensate with increased PT or pelvic retroversion to attempt to maintain anupright posture. Abnormal spinopelvic parameters contribute to multiple spinal conditions including isthmic spondylolysis, degenerative spondylolisthesis, deformity, and impact outcome after spinal fusion. Sagittal balance, pelvic incidence, and all spinopelvic parameters are easily and reliably measured on standing, full-spine (lateral) radiographs, and it is essential to accurately assess and measure these sagittal values to understand their potential role in the disease process, and to promote spinopelvic balance at surgery. In this article, we provide a comprehensive review of the literature regarding the implications of abnormal spinopelvic parameters and discuss surgical strategies for correction of sagittal balance. Additionally, the authors rate and critique the quality of the literature cited in a systematic review approach to give the reader an estimate of the veracity of the conclusions reached from these reports.

Outcomes following surgical intervention for impending and gross instability caused by multiple myeloma in the spinal column

OBJECT Multiple myeloma is the most common primary tumor of the spine and is the most common primary malignant tumor of bone. Although spinal myeloma is classically a radiosensitive lesion, clinical or radiographic signs of instability merit surgical intervention. The authors present the epidemiology, surgical indications, and outcome data of a series of consecutive cases involving 31 surgically treated patients with diagnoses of multiple myeloma and plasmacytoma of the spine (the largest such series reported to date). METHODS Surgical instability was the criterion for operative intervention in this patient cohort. The Spinal Instability Neoplastic Score (SINS) was used to make this assessment of instability. The cases were analyzed using location of the lesion, spinal levels involved, Frankel score, adjuvant therapy, functional outcome, and patient survival. RESULTS All patients undergoing surgical intervention were determined to have indeterminate or gross spinal column instability according to SINS criteria. The median survival was 78.9 months. No significant difference in survival was seen for patients with higher SINS scores or for older patients (> 55 years). There was a statistically significant difference in survival benefit observed for patients receiving chemotherapy and radiation versus radiation alone as an adjuvant to surgery (p = 0.02). CONCLUSIONS In this 10-year analysis, the authors report outcomes of surgical intervention for patients with indeterminate or gross spinal instability due to multiple myeloma and plasmacytoma of the spine with improved neurological function following surgery and low rates of instrumentation failure.

Incidence and clinical significance of vascular encroachment resulting from freehand placement of pedicle screws in the thoracic and lumbar spine: analysis of 6816 consecutive screws.

Study Design. Retrospective case series. Objective. Evaluate the incidence and clinical significance of vascular encroachment resulting from freehand placement of pedicle screws in the thoracic and lumbosacral spine. Summary of Background Data. Pedicle screws are routinely used to effectively stabilize all 3 columns of the spine but can be technically demanding to place in the setting of variable anatomy. There is a paucity of data regarding iatrogenic major vascular injuries during posterior instrumentation procedures. Methods. We retrospectively reviewed the records of all patients undergoing freehand pedicle screw placement without image guidance in the thoracic or lumbar spine during a 7-year period. The incidence and extent of vascular encroachment by a pedicle screw was determined by review of routine postoperative computed tomographic scans obtained within 24 hours of all surgical procedures. Vascular encroachment was defined as a pedicle screw that was touching or deforming the wall of a major vessel. Results. A total of 964 patients received 6816 freehand-placed pedicle screws in the thoracolumbar spine. Fifteen (0.22%) screws that encroached a major vascular structure were identified. Ten (0.29%) thoracic pedicle screws encroached on the aorta, 4 (0.14%) lumbar screws on the common iliac vein, and 1 S1 screw (0.19%) on the internal iliac vein. In consultation with vascular surgery, it was determined whether revision surgery and the technique/approach for the revision procedure should be recommended. Two (0.21%) patients required revision surgery to remove the encroaching pedicle screw (T5 and T8) due to concern for vascular injury. Both patients were asymptomatic and recovered without further complications after revision surgery. Conclusion. Vascular encroachment of major vessels occurs rarely in the setting of freehand pedicle screw placement in the thoracolumbar spine. Although rare, delayed vascular injury from errant pedicle screw placement has been reported in the literature. The aorta seems to be the vessel at the highest risk of injury. Routine intraoperative or postoperative computed tomographic scanning allows for early identification of pedicle screws encroaching on vascular structures thereby facilitating early revision surgery. Level of Evidence: 4

Safety and efficacy of pedicle screw placement using intraoperative computed tomography: consecutive series of 1148 pedicle screws.

OBJECT A number of imaging techniques have been introduced to minimize the risk of pedicle screw placement. Intraoperative CT has been recently introduced to assist in spinal instrumentation. The aim of this study was to study the effectiveness of intraoperative CT in enhancing the safety and accuracy of pedicle screw placement. METHODS The authors included all cases from December 2009 through July 2012 in which intraoperative CT scanning was used to confirm pedicle screw placement. RESULTS A total of 203 patients met the inclusion criteria. Of 1148 screws, 103 screws (8.97%) were revised intraoperatively in 72 patients (35.5%): 14 (18.42%) were revised in the cervical spine (C-2 or C-7), 25 (7.25%) in the thoracic spine, and 64 (8.80%) in the lumbar spine. Compared with screws in the thoracic and lumbar regions, pedicle screws placed in the cervical region were statistically more likely to be revised (p = 0.0061). Two patients (0.99%) required reoperations due to undetected misplacement of pedicle screws. CONCLUSIONS The authors describe one of the first North American experiences using intraoperative CT scanning to confirm the placement of pedicle screws. Compared with a similar cohort of patients from their institution who had pedicle screws inserted via the free-hand technique with postoperative CT, the authors found that the intraoperative CT lowers the threshold for pedicle screw revision, resulting in a statistically higher rate of screw revision in the thoracic and lumbar spine (p < 0.0001). During their 2.5-year experience with the intraoperative CT, the authors did not find a reduction in rates of reoperation for misplaced pedicle screws.

Subependymoma: clinical features and surgical outcomes.

Abstract Objective: Subependymomas are rare, indolent neoplasms that have been described in the brain and the spinal cord. The purpose of this study is to report the clinical and radiolographic features, and surgical outcomes of this entity. Methods: Twenty-six patients with pathologically-verified subependymomas were treated from 1990 through 2009, with a mean follow-up of 39 months. The clinical and radiological records were reviewed and outcomes analyzed. Results: There were 15 fourth ventricle tumors, 6 lateral ventricle tumors, and 5 spinal tumors. For the intracranial tumors, headaches, changes in vision, and difficulties with balance were the most common symptoms. Most tumors were heterogeneously enhancing and hypointense or isointense to gray matter on T1-imaging and hyperintense on T2-imaging. All patients with tumors in the fourth ventricle underwent a suboccipital craniotomy and seven patients received an additional C1 laminectomy. Patients with lateral ventricular tumors underwent craniotomy with primarily a transcallosal resection. Patients with spinal tumors underwent laminectomy with intramedullary tumor resection. All tumors were resected employing microsurgical techniques. Overall, six patients had a sub-total resection. No recurrence of tumor or symptoms was noted at last follow-up for any patient, suggesting that maximal safe resection is often sufficient to provide symptomatic relief. Three patients had long-term complications from surgery. Tumor location was not associated with age at presentation, resection achieved, or development of complications. Conclusions: Subependymomas are indolent tumors that when symptomatic can present with cerebrospinal fluid (CSF) obstructive symptoms in the brain and myelopathy in the spinal cord. There is no one symptom diagnostic for subependymomas. Surgical treatment can provide long term tumor control.

Classification Schemes of Cranial Dural Arteriovenous Fistulas

The clinical presentation of dural arteriovenous fistulas (DAVFs), in particular the associated risk of intracranial hemorrhage, shows a strong correlation with their pattern of venous drainage. The two most commonly used and clinically accepted DAVF classifications are the Merland-Cognard classification and the Borden classification, both based on the morphology of the venous drainage. A revised classification that grades DAVFs through a combination of angiographic and clinical features has also been proposed. This article offers a review of these various classification schemes, and discusses their application to treatment decision making.

Thromboembolic events and spinal surgery.

Management of patients undergoing neurosurgical spinal procedures requires balancing the competing risks of hemorrhage and thrombosis. Deep venous thrombosis (DVT) and pulmonary embolism (PE) may be significant complications following spinal surgery. The authors reviewed 30 studies regarding thromboembolic events following spinal surgery for various etiologies and analysed all the methods used to prevent thromboembolic events. Despite the low incidence of DVT (2.7%) and PE (2%), most spinal surgeons routinely treat patients with a non-invasive prophylactic method such as pneumatic sequential compression devices or compression stockings. Chemoprophylaxis is another effective method to prevent thromboembolic episodes. Inferior vena cava filters may be a safe and effective method to prevent thromboembolic episodes in this patient cohort when chemoprophylaxis and mechanical compression is contraindicated.

Surgical anatomy of the diaphragm in the anterolateral approach to the spine: A cadaveric study

Study Design: Laboratory cadaveric study. Objective: To delineate the pertinent surgical anatomy of the diaphragm during access to the anterolateral thoracolumbar junction. Summary of Background Data: The general anatomy of the thoracic diaphragm is well described. The specific surgical anatomy as it pertains to the lateral and thoracoabdominal approaches to the thoracolumbar junction is not well described. Methods: Dissections were performed on adult fresh cadaveric specimens. Special attention was paid to the diaphragmatic attachments to the lower rib cage and to the spinal thoracolumbar junction. Results: The pertinent diaphragmatic attachments to the rib cage are at the 11th and 12th ribs. Whether the diaphragm is incised or mobilized ventrally, the pertinent spinal attachments are the lateral and medial arcuate ligaments. Identifying and sectioning these structures allows for direct access to the thoracolumbar junction, particularly the L1 vertebral body. Conclusions: An understanding of the diaphragmatic-costal and diaphragmatic-spinal attachments is key for the safe and effective implementation of diaphragm mobilization during the lateral and thoracoabdominal approaches to the spine.

Impact of tethered cord release on symptoms of Chiari II malformation in children born with a myelomeningocele

PurposeThe role of distal traction in the form of a tethered spinal cord in exacerbating anatomical findings or symptoms of Chiari II malformation (CIIM) has been debated for decades. Despite the association of Chiari II malformation with myelomeningocele, the impact of tethered cord release on CIIM symptoms in patients has not been explored.MethodsA retrospective review of 59 patients born with a myelomeningocele was performed. A total of 92 untethering procedures were performed in which symptoms of CIIM were present in 29 cases. In 57 out of 92 cases, the patients did not have symptoms of CIIM prior to untethering. Six cases were excluded because cervicomedullary decompression was performed prior to untethering. The response of CIIM symptoms, syrinx size, and cerebellar tonsil position were examined before and after spinal cord untethering.ResultsForty-four characteristic signs and symptoms of CIIM were present prior to 29 untetherings. Thirty-three of 44 (75%) symptoms improved following spinal cord untethering, though no symptom resolved completely. Syrinx size and cerebellar tonsil position were unchanged following untethering.ConclusionThe authors conclude that mild to moderate symptoms of CIIM may respond positively to spinal cord untethering, potentially by normalization cerebrospinal fluid flow dynamics. Symptom improvement occurs despite the lack of radiographic evidence of CIIM resolution.