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Study Design: Case report and literature review., Objective: To describe a unique case of large sacral aneurysmal bone cysts (ABCs) treated with denosumab and review the literature on this rare entity., Summary and Background Data: ABCs are expansile osteolytic lesions that typically contain blood-filled spaces separated by fibrous septa. Standard treatment includes surgical resection or curettage and packing; however, for some spinal lesions, the standard approach is not optimal. One therapeutic strategy is to treat spinal ABC with an agent that targets a pathway that is dysregulated in a disease with similar pathophysiology. The bone destruction in both giant cell tumors of bone and ABCs is mediated by RANK ligand (RANKL) produced by the tumor cells. Denosumab, a human monoclonal antibody to RANKL, is effective in the treatment of giant cell tumors of bone., Methods: We report a case of a large sacral ABC that responded to denosumab. A 27-year-old male developed increasing back pain. Imaging revealed a lytic lesion in the sacrum with no clear solid component and regions where the cortex was difficult to identify. ABC was diagnosed on biopsy. Surgery or radiation treatment was expected to be associated with serious morbidity; therefore, denosumab was given using the regimen for giant cell tumors of bone (120  mg monthly with a loading dose)., Results: The patient's pain gradually resolved after 2 months of treatment. New bone formation with a more clearly defined cortex was evident on computed tomographic scan at 16 weeks and continued to show evidence of improvement at 7 and 12 months. Biopsy at 12 months revealed a hypocellular fibrous stroma with new bone formation and no giant cells., Conclusion: We conclude that denosumab can result in symptomatic and radiological improvement in ABC and may be useful in select cases., Level of Evidence: 5.

Study Design: Retrospective study comparing cranial facet joint violation rates of open and percutaneous pedicle screws inserted using 3-dimensional image-guidance., Objective: To determine the rate of cranial facet joint violation in intraoperative computed tomography (CT) image-guided lumbar pedicle screw instrumentation and compare facet joint violation rates between CT image-guided open and percutaneous techniques., Summary of Background Data: Facet joint violation by pedicle screws can potentially result in a higher rate of adjacent segment degeneration. Reported cranial facet joint violation rates range from 7% to 100%. Intraoperative image-guidance, which has enhanced pedicle screw placement accuracy, may aid in avoiding impingement of the cranial facet joints., Methods: We reviewed 188 cases of 3-dimensional image-guided lumbar pedicle screw instrumentation from November 2006 to December 2011. The cranial screws of each construct were graded by 3 reviewers according to the Seo classification (0 = no impingement; 1 = screw head in contact/suspected to be in contact with joint; 2 = screw clearly invaded the joint) on intraoperative axial CT images. If there was a difference in evaluation, a consensus was reached to arrive at a single grade. The χ2 test was used to determine significance between the open and percutaneous group (α = 0.05)., Results: A total of 370 screws (245 open, 125 percutaneous) were graded. Overall facet joint violation rate was 18.9% (grade 1 = 16.2%, grade 2 = 2.7%). Open technique (grade 1 = 22.4%, grade 2 = 4.1%) had a significantly higher violation rate than percutaneous technique (grade 1 = 4%, grade 2 = 0%) (P < 0.0001). There is a trend of an increasing likelihood of facet joint violation from L1 to L5., Conclusion: The use of intraoperative CT image-guidance in lumbar pedicle screw placement resulted in a facet joint violation rate at the lower end of the reported range in literature. The percutaneous technique has a significantly lower facet violation rate than the open technique., Level of Evidence: 4.

Study Design: A retrospective cohort study reporting the use of intraoperative computed tomography (CT) and image-guided navigation system for the placement of pedicle screws in pediatric compared with adult patients., Objective: To evaluate the accuracy of open pedicle screw placement in pediatric patients using intraoperative CT and 3-dimensional (3D) image-guided navigation., Summary of Background Data: Pedicle screws are widely used in children for the correction of spinal deformity. Navigation systems and intraoperative CT are now available as an adjunct to fluoroscopy and anatomic techniques for placing pedicle screws and verifying screw position., Methods: From 2007 to 2010, 984 pedicle screws were placed in a consecutive series cohort of 50 pediatric patients for spinal deformity correction with the use of intraoperative CT (O-arm, Medtronic, Inc, Louisville, CO) and a computerized navigation system (Stealth, Medtronic, Inc, Louisville, CO). The primary outcome measure for this study is redirection or removal of screw on the basis of the intraoperative CT imaging. During the study period, 1511 screws were placed in adult patients using the same image guidance system., Results: A total of 984 pedicle screws were implanted using real-time navigation, with a mean of 20 screws per patient (range: 2-34). On the basis of intraoperative CT, 35 screws (3.6%) were revised (27 redirected and 8 removed), representing a 96.4% accuracy rate. No patients returned to the operating room because of screw malposition.Of the 1511 screws placed in adult patients, 28 (1.8%) were revised intraoperatively for malposition on CT imaging, for an overall 98.2% accuracy rate. Screw revision thus was more common in the pediatric population (P = 0.008). However, the pediatric screw accuracy rate is significantly higher than the findings from a recent meta-analysis of predominantly nonnavigated screws in children, reporting a 94.9% accuracy rate (P = 0.03)., Conclusion: We report 96.4% accuracy in pediatric pedicle screw placement using intraoperative CT and a 3D navigation system. This is similar to other reports and has better accuracy than a recent meta-analysis of nonnavigated screws in children.

Study Design: Human cadaveric study., Objective: The objective of the study was to determine the accuracy of intraoperative O-arm images in determining pedicle screw position using open dissection as the gold standard., Summary of Background Data: Pedicle screws are widely used in the treatment of various spinal disorders. Postoperative computed tomographic scans are the imaging gold standard to detect pedicle screw malposition. However, a second procedure is necessary if such malpositioned screws have to be revised. The O-arm is an intraoperative scanner that allows revision of a screw without having to return the patient to the operating room for a separate procedure. No previous studies have looked at the accuracy of intraoperative O-arm images in determining pedicle screw position., Methods: This factorial validation study utilized 9 cadavers in a comparison of intraoperative O-arm images and the dissection gold standard. Four hundred sixteen screws were inserted using 3-dimensional image (O-arm) guidance from C2 to S1. The screw positions were randomized into 3 groups: "IN" (fully contained within the pedicle), "OUT-lateral," or "OUT-medial." After screw insertion, O-arm images were obtained and reviewed in a blinded fashion by 3 independent observers. Dissection identified the true position of the screws. Specificity, sensitivity, positive predictive value (PPV), and negative predictive value (NPV) were calculated using dissection results as the gold standard. The interobserver reliability was also determined., Results: The overall accuracy, specificity, sensitivity, PPV, and NPV of O-arm images for the thoracic and lumbar spine were 73%, 76%, 71%, 74%, and 72%, respectively. Accuracy of surgeon perception in the cervical spine was significantly less than in the thoracic and lumbosacral spine. There was substantial interobserver agreement between the 3 readers., Conclusion: Intraoperative O-arm images accurately detect significant pedicle screw violations in the thoracic and lumbosacral spine but are less accurate for the cervical spine.

Study Design: Human Cadaveric Experimental Study., Objective: To determine the validity of surgeon perception of pedicle screw position inserted using intraoperative three-dimensional (O-arm) image-guided screw insertion., Summary of Background Data: A surgeon's ability to detect pedicle wall violations intraoperatively is crucial for optimal pedicle screw placement. Accuracy of use of a probe or sound to assess pedicle breach is not optimal and may require experience. Intraoperative navigation has been shown to improve screw placement accuracy. It has not been shown, however, whether navigation in combination with screw tract palpation can further increase the surgeon's ability to detect a pedicle breach in pedicle screw placement in the cervical, thoracic, and lumbosacral spine., Methods: Four hundred eighteen screws were inserted using three-dimensional image guidance transpedicularly from C2 to S1 in 10 fresh frozen cadavers. Screw tracts were created using navigation and then probed. After probing, the surgeon stated whether he perceived that the screw would be in, out laterally, or out medially. After screw insertion for all the levels, open dissection was then performed to determine the actual pedicle screw position. The surgeon's perception of screw position was compared to the dissection results., Results: The overall specificity, sensitivity, positive predictive value, and negative predictive value of the surgeon perception of pedicle screw position were 87%, 80%, 78% and 88%, respectively. Accuracy of surgeon perception of pedicle screw position was significantly less than in the cervical spine when compared with thoracic and lumbosacral spine., Conclusion: Surgeon perception of a navigated pedicle screw position is accurate in the thoracic and lumbar spine. Detection of pedicle screw violations by surgeon perception in the cervical spine is less accurate and does not reliably lead to accurate screw placement.

Study Design: A 20-year magnetic resonance imaging (MRI) and functional outcome follow-up study was performed on patients who had undergone anterior lumbar interbody fusion., Objectives: The objectives of the present study are to determine whether or not degeneration is related to adjacent level fusion and the clinical significance of this degeneration., Summary of Background Data: There are concerns that lumbar fusion leads to increase stress at the adjacent levels. However, the clinical significance of this remains unclear., Methods: Thirty-nine patients who underwent lower lumbar anterior lumbar interbody fusion and who had normal preoperative discograms at the level adjacent level were evaluated with a minimum of a 20-year follow-up. MRI scans were performed and independently evaluated for any evidence of degeneration. Functional status was assessed using the Low Back Outcome Scale., Results: Twenty-nine (74.3%) patients had some evidence of degeneration in their lumbar spine and advanced degeneration was identified in 12 (30.7%) patients. Nine (23.1%) patients had advanced degeneration isolated to the adjacent level and 7 (17.9%) patients had evidence of advanced degeneration with preservation at the level adjacent to the fusion. There was no association between function and radiographic degeneration. Only 3 patients required additional surgery as a result of adjacent level degeneration., Conclusion: The prevalence of degenerative changes is similar to other studies involving normal asymptomatic subjects. Furthermore, the majority of degenerative changes seen occurred over multiple levels or at levels not adjacent to the fusion, suggesting that changes seen may be more likely related to constitutional factors as opposed to the increased stresses arising from the original fusion.

Study Design: A convenience literature-based review of the different techniques of posterior lumbar fusion., Objective: To describe the history, specific techniques, and outcomes of different methods of posterior lumbar fusion. The specific methods that were described include 1) uninstrumented posterior, posterolateral, and facet fusion, and 2) instrumented fusion using pedicle screws or facet screws., Summary of Background Data: There are various posterior fusion techniques available for the treatment of degenerative lumbar spine conditions. Each individual technique has specific technical demands, indications, advantages, and disadvantages which should be taken into consideration when performing these procedures., Methods: The published scientific literature on the different methods of posterior lumbar fusion was reviewed. The history, indications, advantages, disadvantages, and clinical and radiographic outcomes were described based on the literature search., Results/conclusions: Posterior fusion techniques have been and will continue to be among the most commonly performed procedures in lumbar spine surgery. The different methods of fusion are well defined, as are the possible complications and outcomes. They are effective techniques when performed on appropriately selected patients by a surgeon knowledgeable in the techniques and indications. Further studies are needed regarding promising but relatively unproven developments such as minimally invasive surgery and the use of osteoinductive agents.

Study Design: A comparative study investigated the use of plain static radiographs, flexion-extension radiographs, and thin-section helical computed tomography (CT) scanning in the assessment of anterior lumbar interbody fusion using carbon fiber cages., Objective: To compare plain static radiographs, flexion-extension radiographs, and thin-section helical computed tomography scans in the assessment of lumbar interbody fusion using carbon fiber cages., Summary of Background Data: Lumbar interbody fusion has become a popular procedure for the treatment of discogenic back pain. However, there currently is no universally accepted radiologic assessment tool for determining fusion, and the definitive criteria for diagnosing a successful interbody fusion in the lumbar spine remains controversial., Methods: Plain static radiographs, flexion-extension radiographs, and helical computed tomography scans were performed on 32 patients (49 levels) 5 years after anterior lumbar interbody fusion using carbon fiber cages and autologous bone. A radiologist assessed fusion using the Hutter method to detect movement, whereas a spinal surgeon measured movement in degrees using the Simmons method. Helical computed tomography scans were assessed for the presence of bridging trabecular bone., Results: The fusion rate was 86% on plain radiographs and 84% with the Hutter method. The fusion rate was 74% with the 2 degrees cutoff, and 96% with the 5 degrees cutoff prescribed by the Food and Drug Administration. Fusion on helical computed tomography scans was observed in 65% of the patients., Conclusions: In the radiologic assessment of interbody fusion using carbon fiber cages, the use of plain radiographs and flexion-extension radiographs produced much higher fusion rates than assessment with thin-section helical computed tomography scans. The thin-section helical computed tomography studies clearly demonstrated the radiographic presence or absence of bridging bone, a property that was not seen with plain static radiographs or flexion-extension radiographs.