Descriptive analysis of Fibulin-3 and the extracellular vesicle marker, Alix, in drusen from a small cohort of postmortem human eyes.

Fibulin-3 (Fib3) is a secreted glycoprotein that is expressed in the retina and has been associated with drusen formation in age-related macular degeneration (AMD). The purpose of this study was to assess whether Fib3 is associated with extracellular vesicles (EVs) in drusen from non-diseased and AMD human donors. De-identified sections of human eyes were received from the National Disease Research Institute (NDRI, Philadelphia). Donor eyes were either non-diseased (no known ocular pathology) or had been diagnosed with AMD. Retinal cryostat sections were labeled with primary antibodies targeted to Fib3, Apolipoprotein E (ApoE; a drusen marker), and ALG-2 interacting protein X (Alix, an EV marker) for confocal imaging (Leica TCS SP8). Fib3-positive (Fib3+) puncta were detected on the apical region of the RPE layer and within large AMD drusen. Alix-positive (Alix+) puncta were also detected in a single AMD druse, where a number were Fib3+ and the remaining were Fib3-negative. Similarly, there were Fib3+ puncta that were Alix-negative. Fib3 and Alix also showed a degree of colocalization in the photoreceptor outer segments of the neural retina. Our data suggest that the Alix+ puncta are EV-rich populations that accumulate, together with Fib3, within the drusen matrix during AMD. The EV population is likely heterogeneous, such that there are sub-populations with different cargo content.

The biomechanical cost of variable angle locking screws.

INTRODUCTION: Variable angle (VA) locking plates in fracture fixation surgery allow screws to be fastened to the plate within a conical "locus of vectors" in order to avoid existing prostheses, joint surfaces, or poor quality bone. Clinical failures of VA constructs in which screws have rotated at the plate/screw interface have been reported raising the concern that there may be a biomechanical cost for the increased flexibility that VA provides. The objective of this study was to test the mechanical properties of one commonly used VA locking mechanism with screws placed in both nominal and off-axis trajectories and compare these against the standard locking mechanism. METHODS: VA locking screws were inserted into plates for distal femur fractures (VA Curved Condylar) at various angles (0° to 15° away from perpendicular). A control group of standard locking screws/plates was also tested. Maximum moment at the screw/plate interface and moment at two reference displacements were determined. RESULTS: VA screws locked perpendicular to the plate provided the greatest maximum moment and moment at the reference displacements when using the VA system, and demonstrated lower moments compared to standard locking screws/plates (p<0.001). Based on linear regression, there was an average decrease of approximately 0.4 Nm screw-plate interface strength for every 1° increase in screw-plate angle (p<0.001). Decreases (p<0.05) were discovered in both maximum moment and moment at the reference displacements for screws locked at 5° relative to those locked at 0°, 10° relative to 0°, and 15° relative to 10°. DISCUSSION: Standard locking systems provided greater resistance to rotational failure at the screw/plate interface than variable angle locking systems. Variable angle systems provided the greatest resistance to rotation when the screw was inserted perpendicular to the plate. As the off-axis angle increased, the resistance to rotation at the screw/plate interface decreased almost linearly. It is unknown if these differences are clinically significant in an actual fracture construct, but recent reported failures in the distal femur suggest that they might be. CONCLUSION: Surgeons should weigh the risks and benefits of VA systems and attempt to minimize the off-axis angle magnitude when VA systems are selected.