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In the United States, nearly 1.2 million people > 12 years old have human immunodeficiency virus (HIV), which is associated with postoperative complications following orthopedic procedures. Little is known about how asymptomatic HIV (AHIV) patients fare postoperatively. This study compares complications after common spine surgeries between patients with and without AHIV. The Nationwide Inpatient Sample (NIS) was retrospectively reviewed from 2005-2013, identifying patients aged > 18 years who underwent 2-3-level anterior cervical discectomy and fusion (ACDF), ≥4-level thoracolumbar fusion (TLF), or 2-3-level lumbar fusion (LF). Patients with AHIV and without HIV were 1:1 propensity score-matched. Univariate analysis and multivariable binary logistic regression were performed to assess associations between HIV status and outcomes by cohort. 2-3-level ACDF ( n = 594 total patients) and ≥4-level TLF ( n = 86 total patients) cohorts demonstrated comparable length of stay (LOS), rates of wound-related, implant-related, medical, surgical, and overall complications between AHIV and controls. 2-3-level LF ( n = 570 total patients) cohorts had comparable LOS, implant-related, medical, surgical, and overall complications. AHIV patients experienced higher postoperative respiratory complications (4.3% vs. 0.4%,). AHIV was not associated with higher risks of medical, surgical, or overall inpatient postoperative complications following most spine surgical procedures. The results suggest the postoperative course may be improved in patients with baseline control of HIV infection.

Study Design: A cross section of Web sites accessible to the general public was surveyed., Objective: To evaluate the quality and accuracy of information on scoliosis that a patient might access on the Internet., Summary of Background Data: The Internet is a rapidly expanding communications network with an estimated 765 million users worldwide by the year 2005. Medical information is one of the most common sources of inquires on the Web. More than 100 million Americans accessed the Internet for medical information in the year 2000. Undoubtedly, the use of the Internet for patient information needs will continue to expand as Internet access becomes more readily available. This expansion combined with the Internet's poorly regulated format can lead to problems in the quality of information available. Since the Internet operates on a global scale, implementing and enforcing standards have been difficult. The largely uncontrolled information can potentially negatively influence consumer health outcomes., Methods: To identify potential sites, five search engines were selected and the word "scoliosis" was entered into each search engine. A total of 50 Web sites were chosen for review. Each Web site was evaluated according to the type of Web site, quality content, and informational accuracy by three board-certified academic orthopedic surgeons, fellowship trained in spinal surgery, who each has been in practice for a minimum of 8 years. Each Web site was categorized as academic, commercial, physician, nonphysician health professional, and unidentified. In addition, each Web site was evaluated according to scoliosis-specific content using a point value system of 32 disease-specific key words pertinent to the care of scoliosis on an ordinal scale. A list of these words is given. Point values were given for the use of key words related to disease summary, classifications, treatment options, and complications. The accuracy of the individual Web site was evaluated by each spine surgeon using a scale of 1 to 4. A score of 1 represents that the examiner agreed with less than 25% of the information while a score of 4 represents greater than 75% agreement., Results: Of the total 50 Web sites evaluated, 44% were academic, 18% were physician based, 16% were commercial, 12% were unidentified, and 10% were nonphysician health professionals. The quality content score (maximum, 32 points) for academic sites was 12.6 +/- 3.8, physician sites 11.3 +/- 4.0, commercial sites 11 +/- 4.2, unidentified 7.6 +/- 3.9, and nonphysician health professional site 7.0 +/- 1.8. The accuracy score (maximum, 12 points) was 6.6 +/- 2.4 for academic sites, 6.3 +/- 3.0 for physician-professional sites, 6.0 +/- 2.7 for unidentified sites, 5.5 +/- 3.8 for nonphysician professional sites, and 5.0 +/- 1.5 for commercial Web sites. The academic Web sites had the highest mean scores in both quality and accuracy content scores., Conclusion: The information about scoliosis on the Internet is of limited quality and poor information value. Although the majority of the Web sites were academic, the content quality and accuracy scores were still poor. The lowest scoring Web sites were the nonphysician professionals and the unidentified sites, which were often message boards. Overall, the highest scoring Web site related to both quality and accuracy of information was www.srs.org. This Web site was designed by the Scoliosis Research Society. The public and the medical communities need to be aware of these existing limitations of the Internet. Based on our review, the physician must assume primary responsibility of educating and counseling their patients.

Background Context: Posterior screw placement techniques have been previously described. Each technique differs with respect to starting point, lateral angulation and sagittal orientation., Purpose: To examine the potential for injury to critical anatomic structures, such as nerve roots and vertebral arteries, during posterior cervical screw placement and to determine safe screw placement., Study Design/setting: An anatomic study was conducted to determine the optimal screw angulation for posterior cervical lateral mass screws. SPECIMEN SAMPLE: Ten fresh-frozen human cadaveric cervical spine specimens were used, consisting of four females and six males, ranging in age from 32 to 68 years., Outcome Measures: Angular measurements and distance from nerve root and vertebral arteries were measured with a single caliper and recorded. One millimeter of proximity to a vital structure was considered a violation of that structure., Methods: Ten fresh-frozen human cadaveric cervical spine specimens were instrumented from C2 to C7 by a single surgeon. Kirschner wires (2.0 mm) were used to reproduce the Roy-Camille, Anderson and Magerl screw trajectories. The wire was drilled through each lateral mass, simulating overdrill error. Each technique was instrumented according to the original description and with additional modifications. The modification consisted of varying the angle of screw placement in the axial plane of the original description from 0 to 30 degrees. Distances to the closest neurovascular structures were averaged for all assays., Results: The Magerl technique is safe at the standard position and modified positions of 20 degrees and 30 degrees from C3-C6. The Roy-Camille technique frequently violates neurovascular structures below C3, especially the nerve root with more lateral screw angulation. The standard technique is noted to have good bone purchase only at C2 and C3. The Anderson technique is safe at 20 degrees and 30 degrees modified positions from C3-C7. Posterior screw placement at the C7 vertebral level was safe only with a modified Anderson technique of 20 degrees and 30 degrees of lateral screw angulation., Conclusions: The present study indicates that there are significant differences of potential neurovascular injury, which is dependent on the technique used for screw entry, the level instrumented and the angle of screw trajectory in the parasagittal plane.

Background Context: The goal of spinal instrumentation is to stabilize involved motion segments while fusion occurs. Although some degree of load sharing is necessary for fusion, the ability of the instrumentation system to transfer the load may vary., Purpose: The purpose of this study is to formulate a mathematical relationship between load sharing and load transfer of specific spinal instrumentation systems using a well-accepted mechanical model., Study Design/setting: Forty-eight American Society for Testing Materials standard ultra high molecular weight polyethylene cylinders were used as per designation F 1717-96, standard test methods for static and fatigue for spinal implant constructs in a corpectomy model., Methods: Twenty-four spinal assemblies consisting of anterior plates, anterior rod, and posterior rods were subjected to compression bending tests using a MTS Bionix servo-hydraulic material testing apparatus. Each implant was tested in compression bending with and without the addition of a titanium load-sharing cage. The force applied was the independent variable, and the displacement was the dependent variable. The stiffness was determined for each setup with and without the addition of an anterior load-sharing cage., Results: The average axial compressive stiffness of a system increased by a factor of 8.5 with the addition of the load-sharing cage. An inverse relationship existed between the compressive stiffness of the construct and its relative increase achieved with the addition of the load-sharing cage. The compressive stiffness of the system with the addition of the load-sharing cage approached that of the anterior device itself as the system flexibility increased. The ability of instrumentation systems to load share or load transfer and their respective stiffness was determined., Conclusions: The 5-mm rod screw posterior system was compared with the 7-mm Ti posterior system with the addition of one and two devices for transverse traction (DTTs). The rods with the increased diameter had a stiffness of 1723 n/mm with one DTT and 1815 n/mm with two DTTs. The addition of an anterior cage had little effect on the stiffness of these systems. Anterior plate and screw/rod systems were analyzed and showed similar mechanical behavior to the 5-mm posterior rod/screw systems. A significant increase in stiffness was realized with the addition of an anterior cage. A means to determine the load sharing/transferring properties of a spinal instrumentation system is presented. This technique will allow the amount of load transferred from the fusion mass to the instrumentation to be predicted.

Study Design: A three-group design with consistent pullout strength measures., Objectives: To determine pullout strength of three fixation types (unicortical screws, bicortical screws, wires) and to investigate their correlation with respect to occipital morphology., Summary of Background Data: A secured, multidirectional occipitocervical fusion requires internal fixation. Devices secured at occipital protuberance were suggested to offer the greatest pullout strength because of this region's thickness., Methods: Twelve fresh human cadaveric occiputs were sketched with a grid delineating 21 fixation sites. Each site was drilled and hand-tapped. Four specimens were instrumented with unicortical screws on one side of the midline and bicortical screws on the other. Another four were instrumented with bicortical screws and wires, and the remaining four were instrumented with unicortical screws and wires. Two points on each specimen were secured with identical fixation to examine side-to-side symmetry. An MTS materials testing apparatus (MTS Systems Corporation, Eden Prairie, MN) was used to displace the fixators. Pullout strengths at different anatomic locations were recorded., Results: The greatest pullout strength was at the occipital protuberance for all fixation types. The bicortical pullout strength was 50% greater than unicortical. The wire pullout strength was not significantly different from that of the unicortical screw (P > 0.05). Seventy-eight percent of wires broke at 1100 N. Unicortical pullout strength at occipital protuberance was comparable with that of the bicortical screw at other locations., Conclusions: Unicortical screw fixation at occipital protuberance offers acceptable pullout strength without the potential complications of bicortical screws or wire fixation.

Study Design: One hundred twelve fresh cadaveric spines were harvested using a newly described technique., Objectives: To develop and describe a technique for the expeditious excision of intact human cadaveric spines for biomechanical testing, to educate the dissector on the health and safety issues involved in harvesting spinal specimens, and to review the present recommendations for storage and preservation of spinal segments., Summary of the Background Data: As the need for biomechanical spinal research continues to expand, the demand for fresh human cadaveric vertebral specimens increases. Previous techniques for harvesting are simplistic and sparse. This technique offers a reliable and expeditious method for procurement of spinal vertebral segments of any size., Methods: Human cadaveric spines were harvested using an adaptation of previous posterior spinal approaches. Techniques for sectioning each vertebral region were developed. Detailed description of these techniques was meticulously documented. The procured spinal segments have been used for multiple biomechanical investigations., Results: The technique has been used successfully in more than 100 spinal harvests. Approximate time required is 30 minutes. The harvested segments have been reliable biomechanical specimens in many published studies., Conclusions: A new technique for the rapid extraction of human cadaveric spines has been developed. Dissectors may benefit from the recommendations offered for sectioning of each region.

Study Design: The authors present the results of an anatomic study of the human occiput to delineate appropriate screw placement sites., Objectives: Occipital bone morphologic characteristics were evaluated to determine whether significant variability exists and to determine the position of greatest bone thickness for safe and effective internal fixation., Summary of Background Data: New instrumentation and techniques for occipital fixation are being developed in response to concerns about occipital bone variability. Thirty cadaveric occiputs were evaluated to determine if such variability exists and the location of greatest bone thickness. Radial thickness, occipital locations, and gender differences, were determined., Methods: Twenty-six skulls were sectioned sagittally to determine the contributions of the inner, middle, and outer tables to overall occipital thickness. The angle required to gain maximal cortical purchase was determined. Mean values and variance were analyzed statistically to determine variability and thickness. Data was plotted in three dimensions. Variability in morphologic features was minimal., Results: The internal occipital protuberance-external occipital protuberance was thickest at 17.55 mm (SD = 3.18 mm) and was consistently located on the superior nuchal line 43 degrees from the horizontal skull base line. Bone thickness decreased radially from the central internal occipital protuberance position. Bone thickness above the superior nuchal line exceeded that below by 2.74 mm (P < 0.05) vertically and at the oblique positions (P < 0.05). Bone to the right of the midline was only 1 mm thicker than that to the left. Gender differences were minimal. The inner table contributed only 10% to overall occipital thickness. As occipital thickness decreased, the optimal purchase angle increased., Conclusions: Unicortical purchase at and above the superior nuchal line is warranted with a low risk of intracranial venous penetration. Internal fixation devices developed in response to occipital bone variability should be considered with respect to occipital bone thickness distributions. Attention to cervical morphologic characteristics should result in higher success rates in occipitocervical arthrodesis.

Study Design: Computed tomography scans of the dens were performed on patients who had no atlantoaxial pathology., Objectives: To determine whether one or two screws is optimal for fracture fixation and whether two screws can always negotiate the intramedullary odontoid cavity., Summary of Background Data: Fixation of Type II dens fractures traditionally has used C1-C2 posterior wiring and fusion. Two screws placed across an odontoid fracture as a method of rigid internal fixation also has been described. However, it is not known whether two screws can always negotiate the odontoid canal., Methods: Ninety-two consecutive computerized tomography scans of the dens were performed on adults who had no atlantoaxial pathology. Measurements were taken from the scan and compared with the cross-sectional diameter of two odontoid screws., Results: The critical diameter for the placement of two 3.5-mm cortical screws with tapping was 9.0 mm. This dimension was present in 95% of the patients studied., Conclusions: Correct orientation of the computerized tomography scanner is critical for accurate measurements. Two 3.5-mm screws can be used in internal fixation of Type II dens fractures in 95% of the patients if the inner cortex is tapped.