Purpose Six different mono-axial and poly-axial distal humeral plating systems with an anatomical plate design were compared. The aim of the biomechanical tests was to examine differences regarding system stiffness, median fatigue limit, and failure mechanisms. Methods Different configurations of two double plate fixation systems by two manufacturers for the treatment of complex distal humeral fractures (AO/OTA type C2.3) were biomechanically tested in a physiologically relevant setup. Results The 180°Stryker configuration presented itself as the system with the highest stiffness, being significantly stiffer (p < 0.001) than every system other than the poly-axial 180°aap system (p = 0.378). For the median fatigue limit the 180°S tryker and poly-axial aap systems were ranked first and second. The failure mechanism for all 90°systems was a fatigue breakage of the posterolateral plate. The 180°aap systems demonstrated breakage of the most distal screws of the lateral plate. The 180°Stryker system demonstrated screw breakage on both the medial and lateral plates. Discussion Breakage of the posterolateral plate as a failure mechanism for the 90°systems was expected. The 180°s ystems demonstrated a higher stiffness compared to the 90°c onstructs for the axial loading. In conclusion, both poly-axial anatomical plating systems provide sufficient stability in this scenario, and the 180°configurations demonstrated superior stiffness.
Hexapod-ring-fixators have a characteristic rattling sound during load changes due to play in the hexapod struts. This play is perceived as unpleasant by patients and can lead to frame instability. Using slotted-ball-instead of universal-joints for the ring-strut connection could potentially resolve this problem. The purpose of the study was to clarify if the use of slotted-ball-joints reduces play and also fracture gap movement. A hexapod-fixator with slotted-ball-joints and aluminum struts (Ball-Al) was compared to universal-joint-fixators with either aluminum (Uni Al) or steel struts (Uni Steel). Six fixator frames each were loaded in tension, compression, torsion, bending and shear and mechanical performance was analyzed in terms of movement, stiffness and play. The slotted-ball-joint fixator was the only system without measurable axial play (<0.01 mm) compared to Uni-Al (1.2 ± 0.1) mm and Uni-Steel (0.6 ± 0.2) mm (p≤0.001). In both shear directions the Uni-Al had the largest play (p≤0.014). The resulting axial fracture gap movements were similar for the two aluminum frames and up to 25% smaller for the steel frame, mainly due to the highest stiffness found for the Uni-Steel in all loading scenarios (p≤0.036). However, the Uni-Steel construct was also up to 29% (450 g) heavier and had fewer usable mounting holes. In conclusion, the slotted-ball-joints of the Ball-Al fixator reduced play and minimized shear movement in the fracture while maintaining low weight of the construct. The heavier and stiffer Uni-Steel fixator compensates for existing play with a higher overall stiffness.
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