Anatomical and Technical Considerations of Robot-Assisted Cervical Pedicle Screw Placement: A Cadaveric Study.

STUDY DESIGN: Cadaver study. OBJECTIVES: Assess the feasibility of robot-assisted cervical pedicle screw (RA-CPS) placement and understand the anatomical considerations of this technique. METHODS: Four cadaver specimens free from bony pathology were acquired. Anatomical considerations, such as pedicle width (PW) and height (PH), transverse pedicle angle (TPA), and maximal screw length (MSL), were recorded from preoperative computational tomography (CT) scans. Intraoperative cone-beam CT was acquired and registered to the robotic system. After cervical levels were segmented, screw sizes and trajectories were planned, and RA-CPS were placed. Accuracy was assessed using Gertzbein and Robbin's classification on postoperative CT scans. RESULTS: Thirty-five RA-CPS were placed. Major breaches (≥Grade C) occurred in 28.57% screws. Grade A or B accuracy was found in 71.43% of screws, with the most common direction of breach being medial (81.3%). The greatest proportion of breach per level occurred in the upper subaxial levels, (C3:71.4%, C4 66.6%, C5:50%) which had the smallest PW (C3: 4.34 ± .96 mm, C4: 4.48 ± .60, C5: 5.76 ± 1.11). PH was greatest at C2 (8.14 ± 1.89 mm) and ranged subaxial from 6.36 mm (C3) to 7.48 mm (C7). The mean PW was 5.37 mm and increased caudally from 4.34 mm (C3) to 6.31 mm (C7). The mean TPA was 39.9° and decreased moving caudally 46.9°) to C7 (34.4°). The MSL was 37.1 mm and increased from C2 (26.3 mm) to C7 (41.0 mm). CONCLUSION: RA-CPS has the potential to be feasible, but technological and instrument modifications are necessary to increase the accuracy in the cervical region.

Chromatin architecture around stroke haplotypes provides evidence that genetic risk is conferred through vascular cells.

Introduction: Genome-wide association studies (GWAS) have identified numerous stroke-associated SNPs. To understand how SNPs affect gene expression related to increased stroke risk, we studied epigenetic landscapes surrounding 26 common, validated stroke-associated loci. Methods: We mapped the SNPs to linkage disequilibrium (LD) blocks and examined H3K27ac, H3K4me1, H3K9ac, and H3K4me3 histone marks and transcription-factor binding-sites in pathologically relevant cell types (hematopoietic and vascular cells). Hi-C data were used to identify topologically associated domains (TADs) encompassing the LD blocks and overlapping genes. Results: Fibroblasts, smooth muscle, and endothelial cells showed significant enrichment for enhancer-associated marks within stroke-associated LD blocks. Genes within encompassing TADs reflected vessel homeostasis, cellular turnover, and enzymatic activity. Conclusions: Stroke-associated genetic variants confer risk predominantly through vascular cells rather than hematopoietic cell types.

Previous studies have found several variations in the DNA sequence (known as single nucleotide polymorphisms) linked to higher stroke risk. But the mechanisms behind how they increase risk is unknown. One hypothesis is that they affect non-coding DNA elements (i.e., epigenetics), which in turn drive abnormal changes in gene expression leading to increased stroke risk. To investigate this potential mechanism, we mined publicly available, cell-type specific databases. We searched for overlap between the regions with polymorphisms and regions where DNA transcription machinery bind (i.e., enhancers, transcription factor binding sites). We found that fibroblasts and smooth muscle cells (cells in vessel walls) had more of these DNA elements in regions associated with stroke risk. Bioinformatics analyses of genes that could be affected by changes in these elements were linked to stroke-related mechanisms.

Epigenetic landscapes of intracranial aneurysm risk haplotypes implicate enhancer function of endothelial cells and fibroblasts in dysregulated gene expression.

BACKGROUND: Genome-wide association studies have identified many single nucleotide polymorphisms (SNPs) associated with increased risk for intracranial aneurysm (IA). However, how such variants affect gene expression within IA is poorly understood. We used publicly-available ChIP-Seq data to study chromatin landscapes surrounding risk loci to determine whether IA-associated SNPs affect functional elements that regulate gene expression in cell types comprising IA tissue. METHODS: We mapped 16 significant IA-associated SNPs to linkage disequilibrium (LD) blocks within human genome. Using ChIP-Seq data, we examined these regions for presence of H3K4me1, H3K27ac, and H3K9ac histone marks (typically associated with latent/active enhancers). This analysis was conducted in several cell types that are present in IA tissue (endothelial cells, smooth muscle cells, fibroblasts, macrophages, monocytes, neutrophils, T cells, B cells, NK cells). In cell types with significant histone enrichment, we used HiC data to investigate topologically associated domains (TADs) encompassing the LD blocks to identify genes that may be affected by IA-associated variants. Bioinformatics were performed to determine the biological significance of these genes. Genes within HiC-defined TADs were also compared to differentially expressed genes from RNA-seq/microarray studies of IA tissues. RESULTS: We found that endothelial cells and fibroblasts, rather than smooth muscle or immune cells, have significant enrichment for enhancer marks on IA risk haplotypes (p < 0.05). Bioinformatics demonstrated that genes within TADs subsuming these regions are associated with structural extracellular matrix components and enzymatic activity. The majority of histone marked TADs (83% fibroblasts [IMR90], 77% HUVEC) encompassed at least one differentially expressed gene from IA tissue studies. CONCLUSIONS: These findings provide evidence that genetic variants associated with IA risk act on endothelial cells and fibroblasts. There is strong circumstantial evidence that this may be mediated through altered enhancer function, as genes in TADs encompassing enhancer marks have also been shown to be differentially expressed in IA tissue. These genes are largely related to organization and regulation of the extracellular matrix. This study builds upon our previous (Poppenberg et al., BMC Med Genomics, 2019) by including a more diverse set of data from additional cell types and by identifying potential affected genes (i.e. those in TADs).