Comparison of outcomes and operative course between septic and aseptic nonunion in long bones.

PURPOSE: The treatment of nonunion of long bones is difficult particularly in the presence of infection, which often involves staged surgical management. There is limited literature to compare the post operative course and outcomes of patients treated for septic versus aseptic nonunion. Thus, the purpose of this study was to determine if a difference exists between the number of surgical procedures, time to union, and rate of successful union for these two groups. METHODS: A retrospective cohort study was performed at a single tertiary care center. Patients suffering nonunion of the humerus, tibia and femur were included. Patient demographic data and characteristics of the post operative course were collected to include number and reason for repeat operations, antibiotic course, time to union, and development of a successful union. RESULTS: About 28 of 122 patients had septic nonunion. After diagnosis of nonunion, the septic group averaged 3.9 surgeries compared to 1.5 in the aseptic group (p < 0.001). There was no difference in the rate of successful union (79.8% versus 85.7%; p = 0.220), though the septic group took 129 days longer on average for successful union. (376 versus 247; p = 0.018). CONCLUSION: Septic nonunion of long bones is associated with the need for significantly more operations as well as time to union, though union rates remain similar. The identification of infection is critical for both the appropriate treatment as well as counseling patients on the expected post operative course.

Mimicking Ribosomal Unfolding of RNA Pseudoknot in a Protein Channel.

Pseudoknots are a fundamental RNA tertiary structure with important roles in regulation of mRNA translation. Molecular force spectroscopic approaches such as optical tweezers can track the pseudoknot's unfolding intermediate states by pulling the RNA chain from both ends, but the kinetic unfolding pathway induced by this method may be different from that in vivo, which occurs during translation and proceeds from the 5' to 3' end. Here we developed a ribosome-mimicking, nanopore pulling assay for dissecting the vectorial unfolding mechanism of pseudoknots. The pseudoknot unfolding pathway in the nanopore, either from the 5' to 3' end or in the reverse direction, can be controlled by a DNA leader that is attached to the pseudoknot at the 5' or 3' ends. The different nanopore conductance between DNA and RNA translocation serves as a marker for the position and structure of the unfolding RNA in the pore. With this design, we provided evidence that the pseudoknot unfolding is a two-step, multistate, metal ion-regulated process depending on the pulling direction. Most notably, unfolding in both directions is rate-limited by the unzipping of the first helix domain (first step), which is Helix-1 in the 5' → 3' direction and Helix-2 in the 3' → 5' direction, suggesting that the initial unfolding step in either pulling direction needs to overcome an energy barrier contributed by the noncanonical triplex base-pairs and coaxial stacking interactions for the tertiary structure stabilization. These findings provide new insights into RNA vectorial unfolding mechanisms, which play an important role in biological functions including frameshifting.

Nanopore electric snapshots of an RNA tertiary folding pathway.

The chemical properties and biological mechanisms of RNAs are determined by their tertiary structures. Exploring the tertiary structure folding processes of RNA enables us to understand and control its biological functions. Here, we report a nanopore snapshot approach combined with coarse-grained molecular dynamics simulation and master equation analysis to elucidate the folding of an RNA pseudoknot structure. In this approach, single RNA molecules captured by the nanopore can freely fold from the unstructured state without constraint and can be programmed to terminate their folding process at different intermediates. By identifying the nanopore signatures and measuring their time-dependent populations, we can "visualize" a series of kinetically important intermediates, track the kinetics of their inter-conversions, and derive the RNA pseudoknot folding pathway. This approach can potentially be developed into a single-molecule toolbox to investigate the biophysical mechanisms of RNA folding and unfolding, its interactions with ligands, and its functions.