Biomechanical Evaluation of Distal Radioulnar Joint Instability and Adams Procedure.

PURPOSE: Distal radioulnar joint (DRUJ) instability may occur after an injury, resulting in pain and reduced strength. When primary repair is not possible or initial fixation has failed, chronic instability may result, requiring a reconstructive procedure such as the Adams procedure. The first purpose of this study was to evaluate the role of the triangular fibrocartilage complex and various components of the interosseous membrane as they were sectioned. The second purpose was to evaluate the Adams procedure in stabilizing the forearm. METHODS: Eight fresh cadaver forearms were dynamically moved through an average range of 56.8° pronation to 54.8° supination and tested first with the forearm intact and then after sectioning each of the following structures: the dorsal (DRUL) and palmar radioulnar ligaments (PRUL), the distal interosseous membrane, and the central band. Finally, they were tested after reconstruction using the Adams procedure. During each forearm motion and provocative shuck, the motion of the radius and ulna were measured and the locations of the radial attachments of the DRUL, PRUL, and sigmoid notch and ulnar fovea were computed. RESULTS: Significant increases in the gap between the ulnar fovea and the attachment sites of the DRUL and PRUL were observed with incremental sectioning, most notably after sectioning of the central band. Reconstruction significantly reduced the gap at the DRUL and PRUL sites during dynamic motion. CONCLUSIONS: This study reinforces the concept that DRUJ stability depends on more than the radioulnar ligaments, ulnocarpal ligaments, and triangular fibrocartilage complex, but is also significantly affected by the distal and central interosseous membrane. Reconstruction reduces gapping. CLINICAL RELEVANCE: These results suggest that the Adams reconstruction is a reasonable option to address DRUJ instability but may be an incomplete solution in the setting of a ruptured interosseous ligament.

Self-Assembly Simulations of Classic Claudins-Insights into the Pore Structure, Selectivity, and Higher Order Complexes.

Tight junction (TJ) protein assembly controls permeability across epithelial and endothelial cells; thus, biochemical interactions that control the TJ assembly have physiological and biomedical significance. In this work, we employed multiscale simulations to probe the TJ self-assembly of five classic claudins (-1, -2, -4, -15, and -19). Claudin proteins assembled into dimeric and occasionally trimeric interfaces that subsequently formed larger polymeric strands. Using orientation-angle analysis to decompose polymeric strands, we found that individual claudins prefer certain dimer interfaces to others. Despite variations in the exact dimer populations observed in individual claudins, there appears to be an overall conformational uniformity in the type of dimeric interactions formed by the claudin family of proteins. A detailed structural characterization of the trimeric assemblies revealed that they could be putative receptors for trimeric Clostridium perfringens enterotoxin. Full characterization of the claudin-2 dimer interface revealed a cysteine cross-linkable interaction, which could be assembled into a symmetric pore of 7.4 Å average diameter. We extended the analysis of pore structure to other classic claudins and found that the distribution of polar residues lining the pore volume varied considerably between the barrier- and pore-forming claudins, potentially delineating the functionality in classic claudins.