Disease Management in the Genomics Era-Summaries of Focus Issue Papers.

The genomics revolution has contributed enormously to research and disease management applications in plant pathology. This development has rapidly increased our understanding of the molecular mechanisms underpinning pathogenesis and resistance, contributed novel markers for rapid pathogen detection and diagnosis, and offered further insights into the genetics of pathogen populations on a larger scale. The availability of whole genome resources coupled with next-generation sequencing (NGS) technologies has helped fuel genomics-based approaches to improve disease resistance in crops. NGS technologies have accelerated the pace at which whole plant and pathogen genomes have become available, and made possible the metagenomic analysis of plant-associated microbial communities. Furthermore, NGS technologies can now be applied routinely and cost effectively to rapidly generate plant and/or pathogen genome or transcriptome marker sequences associated with virulence phenotypes in the pathogen or resistance phenotypes in the plant, potentially leading to improvements in plant disease management. In some systems, investments in plant and pathogen genomics have led to immediate, tangible benefits. This focus issue covers some of the systems. The articles in this focus issue range from overall perspective articles to research articles describing specific genomics applications for detection and control of diseases caused by nematode, viral, bacterial, fungal, and oomycete pathogens. The following are representative short summaries of the articles that appear in this Focus Issue .

Projection of the lumbar pedicle and its morphometric analysis.

STUDY DESIGN: This study defined the projection point of the lumbar pedicle on its posterior aspect and its relation to a reliable landmark and reported pedicle dimensions based on 50 lumbar spines. OBJECTIVES: To establish the best starting point for a pedicle screw for passing the screw down the center (axis) of the pedicle; to describe quantitatively the relations of the pedicle projection point to a reliable landmark; and to evaluate the linear and angular dimensions of the lumbar pedicle. SUMMARY OF BACKGROUND DATA: Posterior transpedicular screw fixation has been most widely used for management of the unstable lumbar spine. Several studies of pedicular anatomy exist, but little quantitative data regarding the location of the lumbar pedicle axis for each level have been reported. METHODS: Fifty dry lumbar specimens (250 lumbar vertebrae) were obtained for study of the lumbar pedicle. Anatomic evaluation focused on determination of the projection point of the lumbar pedicle axis on the junction of the superior facet and the transverse process and measured the distance from the projection point to the midline of the transverse process for each level of the lumbar vertebrae. Pedicle dimensions, including linear and angular, also were measured. RESULTS: Differences in dimensions between men and women were not found to be statistically significant. The average distance from the projection point to the midline of the transverse process consistently changed from L1 to L5. Above L4, the projection point for men and women averaged 3.9 mm for L1, 2.8 mm for L2, and 1.4 mm for L3 superior to the midline of the transverse process, respectively. At L4, the projection point was close to the midline of the transverse process (0.5 mm inferior). At L5, the projection point was an average of 1.5 mm inferior to the midline of the transverse process. CONCLUSIONS: The average distance from the projection point of the lumbar pedicle axis to the midline of the transverse process consistently varied at different levels. This information may prove helpful in the placement of screws into the lumbar pedicle.

Projection of the S2 pedicle onto the posterolateral surface of the ilium. A technique for lag screw fixation of sacral fractures or sacroiliac joint dislocations.

STUDY DESIGN: This study analyzed the sacroiliac articulation at the level of the second sacral vertebra (S2). Anthropometric measurements were performed on 20 cadaveric pelves to determine the optimal starting point for lag screw fixation of the sacroiliac joint at S2. OBJECTIVES: The measurements were utilized to identify a region on the outer table of the posterior ilium which will provide a starting point for consistent safe placement of a lag screw across the sacroiliac joint into the ala of S2. SUMMARY OF BACKGROUND DATA: Previous studies have defined the optimal starting point on the outer table of the ilium for the projection of lag screws into the ala of S1. No data are available for lag screw fixation of the sacroiliac joint at S2. METHODS: Twenty human cadaveric pelves, disarticulated at the sacroiliac joint and fixed in a holding frame designed to maintain the sacrum and ilium in anatomic reduction, were utilized to identify a point on the outer table of the posterior ilium at which an interfragmentary screw could be inserted into the center of the pedicle of the second sacral vertebra. RESULTS: The starting point on the posterolateral ilium for screw insertion into the center of the S2 pedicle was found to exist 1.5 +/- 0.31 cm superior and 2.5 +/- 0.3 cm posterior to the apex of the greater sciatic notch only when the screw or guide pin was advanced at an angle perpendicular to the long axis of the sacrum. CONCLUSION: During lag screw fixation of posterior pelvic ring disruptions, aberrant screw placement may impose considerable risk to adjacent vascular, visceral, or neural structures. After anatomic reduction of the sacroiliac joint, safe and accurate screw fixation can be achieved by utilizing the starting point and insertion trajectory described in this paper.

Anatomic consideration of C2 pedicle screw placement.

STUDY DESIGN: This anatomic study tested placement of C2 pedicle screws using cadaver specimens. OBJECTIVES: To further assess the safety of transpedicular screw placement in the axis by comparing two surgical techniques. SUMMARY OF BACKGROUND DATA: Transpedicular screw fixation of traumatic spondylolisthesis of the axis has been described in the literature. Recently, anatomic studies and clinical applications of transpedicular screw fixation for traumatic lesions of middle and lower cervical spine have been described. No previous study assessing the safety of C2 pedicle screw placement is available. METHODS: Sixteen embalmed cadaveric specimens were used for this study. In the first eight specimens (Method A), the point of entry for screw placement was chosen to be about 5 mm inferior to the superior border of C2 lamina and 7 mm lateral to the lateral border of the spinal canal. The screw direction was chosen to be about 30 degrees medial to the sagittal plane and 20 degrees cephalad to the transverse plane. A 3.5-mm cortical screw of appropriate length, determined with depth gauge, was placed bilaterally into the C2 pedicle. In the next eight specimens (Method B), the direction of the drill bit was guided directly by the medial and superior aspect of the individual C2 pedicle. Gross dissection was done to view violation of dura, nerve roots, vertebral artery, and penetration of medial, lateral, superior, and inferior cortex of the C2 pedicle. Radiographs and computed tomography scans were obtained to evaluate screw placement in the C2 pedicle. RESULTS: In Method A, four screws had lateral violations into the vertebral artery. In Method B, only two cases of minimal penetration of pedicle cortex were found. No medial, superior, or inferior violation of the pedicle cortex was found in the present study. CONCLUSIONS: The present anatomic study suggests that transpedicular screw fixation may be performed safely in the C2 pedicle by using the second technique. Using the first technique is not safe.