Kalil G. Abdullah

ASSOCIATION BETWEEN FOUR SNPS ON CHROMOSOME 9P21 AND MYOCARDIAL INFARCTION IS REPLICATED IN AN ITALIAN POPULATION

AbstractGenome-wide single nucleotide polymorphism (SNP) association studies recently identified four SNPs (rs10757274, rs2383206, rs2383207, and rs10757278) on chromosome 9p21 that were associated with coronary artery disease (CAD) and myocardial infarction (MI) in Caucasian populations from northern Europe and North America. Our aim was to determine whether these SNPs were associated with MI in a southern Europe/Mediterranean population. We employed a case–control association design involving 416 MI patients and 308 non-MI controls from Italy. Significant allelic association was identified between all four SNPs and MI. The association remained significant after adjusting for covariates for MI (P = 0.007–0.029). One risk haplotype (GGGG; P = 0.028) and one protective haplotype (AAAA; P = 0.047) were identified. Genotypic association analysis demonstrated that the SNPs conferred susceptibility to MI most likely in a dominant model (P = 0.0007–0.013). When the case cohort was divided into a group of MI patients with a family history (n = 248) and one group without it (n = 168), the positive, significant association was identified only in the group with the family history. These results indicate that chromosome 9p21 confers risk for development of MI in an Italian population.

Radiation exposure to the surgeon during percutaneous pedicle screw placement.

Study Design In-vitro radiation exposure study. Objective To determine the radiation exposure to the eyes, extremities, and deep tissue during percutaneous pedicle screw placement. Summary of Background Data Image-guided minimally invasive spinal surgery is typically performed with the use of fluoroscopy, exposing the surgeon and patient to ionizing radiation. The radiation dose to the surgeon has not been reported and risk to the surgeon performing this procedure over the long term is uncertain. Methods Percutaneous pedicle screws were placed in a cadaveric specimen from L2-S1 bilaterally using a cannulated pedicle screw system. Two fluoroscopes were used in the anteroposterior and lateral planes. The surgeon wore a thermolucent dosimeter ring on the right hand and badge over the left chest beneath the lead apron. Complete surgical time was recorded and a computed tomography scan was performed to assess screw placement. Radiation exposure was measured for total time of fluoroscopy use; average exposure per screw, surgical level, and dose to the eyes was calculated. This data was used to define the safety of percutaneous pedicle screw placement. Results Total fluoroscope time for placement of 10 percutaneous pedicle screws was 4 minutes 56 seconds (29 s per screw). The protected dosimeter recorded less than the reportable dose. The ring dosimeter recorded 103 mREM, or 10.3 mREM per screw placed. All screws were within the bone confines with acceptable trajectory. Exposure to the eyes was 2.35 mREM per screw. Conclusions On the basis of this data, percutaneous pedicle screw placement seems to be safe. A surgeon would exceed occupational exposure limit for the eyes and extremities by placing 4854 and 6396 screws percutaneously, respectively. Lead protected against radiation exposure during screw placement. The “hands-off” technique used in this study is recommended to minimize radiation exposure. Lead aprons, thyroid shields, and leaded glasses are recommended for this procedure.

The TaqMan Method for SNP Genotyping

Single nucleotide polymorphisms (SNPs) are common DNA sequence variations that occur at single bases within the genome. SNPs have been instrumental in elucidating the genetic basis of common, complex diseases using genome-wide association studies, candidate gene case-control association studies, and genome-wide linkage analyses. A key to these studies is genotyping of SNPs. Various methods for SNP genotyping have been developed. For a particular genotyping project, the choice of method is dependent on the number of SNPs (n) and the number of DNA samples (m) to be genotyped. For a genome-wide or large-scale project with very high n and small m, the Affymetrix SNP GeneChip and Illumina GoldenGate BeadChips assays are the ideal methods. For a project involving a small number of SNPs (small n) and a large population (high m), the TaqMan assay is the preferred technology as it has high throughput and is highly accurate, precise, time-efficient, and cost-effective. Here, we describe the detailed procedures for TaqMan SNP genotyping assay, including preparation of high-quality DNA samples, the operating protocol, clarification of technical issues, and discussion of several cautionary notes.

Radiation exposure to the spine surgeon in lumbar and thoracolumbar fusions with the use of an intraoperative computed tomographic 3-dimensional imaging system.

Study Design. A prospective clinical research article. Objective. The primary goals were to determine (1) radiation exposure to the spine surgeon with the use of an intraoperative 3-dimensional imaging system and (2) to define the safe distance from the computed tomographic scanner. Summary of Background. Intraoperative radiation exposure to the spinal surgeon has been assessed during 2-dimensional fluoroscopy but has not been investigated during intraoperative 3-dimensional imaging. Methods. Ten patients undergoing lumbar or thoracolumbar fusion were enrolled in a prospective trial to determine the radiation exposure to a spine surgeon standing in the substerile room, with the use of the O-ARM Imaging System (Medtronic, Memphis, TN). A thermolucent digital dosimeter was worn at chest level without a lead apron. Dosimeter readings and distance from the spine surgeon were recorded. Results. Average surgeon exposure was 44.22 ± 17.4 &mgr;rem (range: 17.71–70.76 &mgr;rem). The mean distance from the O-ARM was 4.56 ± .32 m, and the surgeon was exposed for an average of 19.6 ± 5.7 seconds (range: 8.05–28.7 s). The annual number of necessary procedures required to surpass the exposure limit, according to the data presented here, would be 113,071 operations using O-ARM. Hence, the number of necessary procedures for O-ARM use is predicted to be 1,130,710 annual procedures to reach the occupational exposure limits for extremity, skin, and all other organs and 339,213 procedures to reach the limits for the lens of eye. Conclusion. Radiation exposure is minimal to the surgical team during routine use of the O-ARM imaging system. The number of procedures required to surpass occupational exposure limits is high if using appropriate distance from the O-ARM.

Use of diffusion tensor imaging in glioma resection

Diffusion tensor imaging (DTI) is increasingly used in the resection of both high- and low-grade gliomas. Whereas conventional MRI techniques provide only anatomical information, DTI offers data on CNS connectivity by enabling visualization of important white matter tracts in the brain. Importantly, DTI allows neurosurgeons to better guide their surgical approach and resection. Here, the authors review basic scientific principles of DTI, include a primer on the technology and image acquisition, and outline the modalitys evolution as a frequently used tool for glioma resection. Current literature supporting its use is summarized, highlighting important clinical studies on the application of DTI in preoperative planning for glioma resection, preoperative diagnosis, and postoperative outcomes. The authors conclude with a review of future directions for this technology.

Reducing surgical site infections following craniotomy: examination of the use of topical vancomycin

OBJECT Although the use of topical vancomycin has been shown to be safe and effective for reducing postoperative infection rates in patients after spine surgery, its use in cranial wounds has not been studied systematically. The authors hypothesized that topical vancomycin, applied in powder form directly to the subgaleal space during closure, would reduce cranial wound infection rates. METHODS A cohort of 150 consecutive patients who underwent craniotomy was studied retrospectively. Seventy-five patients received 1 g of vancomycin powder applied in the subgaleal space at the time of closure. This group was compared with 75 matched-control patients who were accrued over the same time interval and did not receive vancomycin. The primary outcome measure was the presence of surgical site infection within 3 months. Secondary outcome measures included tissue pH from a subgaleal drain and vancomycin levels from the subgaleal space and serum. RESULTS Vancomycin was associated with significantly fewer surgical site infections (1 of 75) than was standard antibiotic prophylaxis alone (5 of 75; p < 0.05). Cultures were positive for typical skin flora species. As expected, local measured vancomycin concentrations peaked immediately after surgery (mean ± SD 499 ± 37 μg/ml) and gradually decreased over 12 hours. Vancomycin in the circulating serum remained undetectable. Subgaleal topical vancomycin was associated with a lower incidence of surgical site infections after craniotomy. The authors attribute this reduction in the infection rate to local vancomycin concentrations well above the minimum inhibitory concentration for antimicrobial efficacy. CONCLUSIONS Topical vancomycin is safe and effective for reducing surgical site infections after craniotomy. These data support the need for a prospective randomized examination of topical vancomycin in the setting of cranial surgery.

Reoperation rates after anterior cervical discectomy and fusion versus posterior cervical foraminotomy: a propensity-matched analysis.

BACKGROUND CONTEXT Anterior cervical discectomy and fusion (ACDF) and posterior cervical foraminotomy (PCF) are both used to surgically treat patients with cervical radiculopathy and have been shown to have similar outcomes. Nonetheless, ACDF has become increasingly more commonplace compared with PCF, in part because of a pervasive belief that PCF has a higher incidence of required reoperations. PURPOSE To determine the reoperation rate at the index level of ACDF versus PCF 2 years postoperatively. STUDY DESIGN A retrospective case-control. PATIENT SAMPLE All patients that underwent ACDF and PCF for radiculopathy (excluding myelopathy indications) between January 2005 and December 2011. OUTCOME MEASURES Revision surgery within 2 years, at the index level, was recorded. METHODS Propensity score analysis between the ACDF and PCF groups was done, matching for age, gender, race, body mass index, tobacco use, median income and insurance status, primary surgeon, level of surgery, surgery duration, and length of hospital stay. RESULTS Seven hundred ninety patients met the inclusion/exclusion criteria, including 627 ACDF and 163 PCF. Before propensity matching, the PCF group was found to be significantly older and more likely to be male. After matching, there were no significant differences between groups for any baseline characteristics. Reoperation rate at the index level was 4.8% for the ACDF group and 6.4% for the PCF group (p=.7) within 2 years of the initial surgery. Using equivalence testing, based on an a priori null hypothesis that a clinically meaningful difference between the two groups would be ≥5%, we found that the absolute difference of 1.6% was significantly (p=.01) less than our hypothesized difference. CONCLUSIONS This study demonstrates that even after accounting for patient demographics, operative characteristics, and primary surgeon, there are no significant differences in 2-year reoperation rates at the index level between ACDF and PCF. The reoperation rates are statistically equivalent. Thus, spine surgeons can operate via the posterior approach without putting patients at increased risk for revision surgery at the index level.

Morphometric and volumetric analysis of the lateral masses of the lower cervical spine.

Study Design. Morphometric and volumetric analysis. Objective. To define the morphometric and volumetric variance of the lateral masses of C5, C6, and C7. Summary of Background Data. Lateral mass screws are routinely placed throughout the subaxial cervical spine but the morphology of the C7 lateral mass is associated with greater difficulty in obtaining adequate purchase. Previous studies have suggested that modified techniques may be associated with better screw purchase in the C7 lateral mass and subsequent avoidance of complications such as foraminal intrusion and C7–T1 facet joint violation. It is necessary to systematically examine the morphometric and volumetric differences among lower cervical lateral masses in order to define the morphologic differences as this has implication with C7 lateral mass instrumentation. Methods. Morphometric and volumetric analysis was performed on computed tomography scans of the of the lateral masses of C5, C6, and C7 in 25 male and 25 female patients in the axial, coronal, and sagittal planes. Volumetric analysis was conducted by tracing the lateral mass at progressive 1 mm axial slices and images were linked for complex volume calculation. Results. At all levels and for all measurements, men and women differed significantly (P < 0.05). Between C5 and C6, sagittal height differed in both men and women, whereas axial articular process (AP) diameter differed only in males (9.2 mm at C5 vs. 10.5 mm at C6). C7 differed statistically from C5 and C6 as measurements increased in sagittal height, sagittal diagonal height, coronal height (women only), and axial AP diameter (women only). C7 measurements decreased relative to the other levels in medial-to-lateral measurements in the axial plane (12.8 vs. 11.5 mm in men, 11.4 vs. 10.5 mm in women), sagittal thickness and axial AP diameter only differed in women. Importantly, the angulation of the lower cervical spine decreases by approximately 6° moving toward C7. There was no statistical difference in lateral mass volume between any of the vertebrae. Conclusion. The degree of cervical angulation represents a consistent and significant anatomic relationship in the lower cervical spine and may necessitate a modified surgical approach.

Rates of anterior cervical discectomy and fusion after initial posterior cervical foraminotomy

BACKGROUND CONTEXT In select patients, posterior cervical foraminotomy (PCF) and anterior cervical discectomy and fusion (ACDF) result in similar clinical outcomes when used to treat cervical radiculopathy. Nonetheless, ACDF is performed more frequently, in part because of surgeon perception that PCF requires operative revisions more frequently. The present study investigates the rate of ACDF reoperation at the index level after initial PCF. PURPOSE To determine the rate of ACDF after initial PCF and to further describe any patient characteristics or preoperative or operative data that increase the rate of reoperation after PCF. STUDY DESIGN Retrospective chart review. METHODS Demographic, operative, and reoperation information was collected from the electronic medical records for all patients who underwent PCF at one institution between 2004 and 2011. All patients were subsequently contacted by telephone to identify postoperative complications and more conclusively determine whether any revision operation was performed at the index level. RESULTS One hundred seventy-eight patients who underwent a PCF were reviewed, with an average follow-up of 31.7 months. Nine (5%) patients underwent an ACDF revision operation at the index level. The reason for reoperation in these patients included cervical radiculopathy, foraminal stenosis, disc herniation, and cervical spondylosis. Patients who subsequently underwent ACDF at the index level were significantly younger (25 vs. 35 years, p=.03), had lower body mass index (25 vs. 29, p=.01), and more likely to take anxiolytic (56% vs. 22%, p=.04) or antidepressant medication (67% vs. 27%, p=.02), compared with those that did not have a revision operation. CONCLUSIONS This is the first study to determine conversion to ACDF after PCF. The present study demonstrates that PCF is associated with a low reoperation rate, similar to the historical reoperation for ACDF. Accordingly, spine surgeons can operate via a PCF approach without a significant increased risk for ACDF revision surgery at the index level.

The state of lumbar fusion extenders

Study Design. Review of literature. Objective. To evaluate the available literature supporting the use of lumbar fusion extenders in clinical practice. Summary of Background Data. Because of the morbidity associated with the harvest of autologous iliac crest bone grafts, the search for lumber fusion extenders and replacements has accelerated. Many formulations of lumbar fusion extenders have been developed, and it is essential to evaluate clinical literature and available outcome metrics of these extenders. Methods. A review of English-language literature was performed between 1990 and January of 2010 for all literature presenting clinical outcomes of lumbar fusion extenders. After controlling for inclusion and exclusion criteria and assigning levels of evidence, 19 clinical studies were fully reviewed including those for demineralized bone matrix, recombinant human bone morphogenetic protein 2 (rhBMP-2), &bgr;-tricalcium phosphate, and calcium sulfate. Results. The most extensively studied of the lumbar fusion extenders is &bgr;-tricalcium phosphate, especially with regard to its use in adolescent scoliosis correction. The use of rhBMP-2 and demineralized bone matrix is supported only by two and three clinical studies, respectively. Calcium sulfate and other miscellaneous extenders are not conclusively or consistently supported by available clinical studies. Conclusion. Calcium phosphate is the most supported of the lumbar fusion extenders. rhBMP-2 and demineralized bone matrix are supported by smaller bodies of evidence. These formulations are supported by these initial studies but in some cases need to be better examined with regard to side effect profiles.