A biomechanical analysis of plate fixation using unicortical and bicortical screws in transverse metacarpal fracture models subjected to 4-point bending and dynamical bending test.

In the published literature there are controversial data to the biomechanical stability of monocortical comparing to the bicortical fixation of metacarpal fractures. The aim of this study was to compare the biomechanical stability of monocortical and bicortical locking osteosynthesis in quasi-static and dynamic 4-point bending tests of composite third metacarpal bone (4th Gen third metacarpal, Sawbones, Malmö, Sweden) fixed with 7-hole locking plate (XXS System, Biotech-Ortho, Wright, Memphis, TN). The tests to determine quasi-static yield and bending strength as well as fatigue strength were conducted in 4 groups of 10 samples after creating standardized mid-shaft transverse osteotomies using a diamont belt grinder (0.3 mm saw blade). The force applied was the dorsal apex loading, similar to the forces applied to metacarpals during normal finger flexion and extension.In the quasi-static testing, no plate breakage was observed in each group. All metacarpals broke at their thinnest part. The average bending strength of the bicortical samples (10.54 ±â€Š0.998 Nm) was significantly higher comparing to the monocortical samples (8.57 ±â€Š0.894 Nm) (P < .001).In the dynamic loading test, all constructs (8 monocortical samples and 7 bicortical) that failed broke at the osteotomy site and the average fatigue strength did not differ in both groups.Consequently, a unicortical plating method may provide adequate strength and stability to metacarpal fractures based on the results of the cyclical loading representative of in vivo loading.

Biomechanical testing of a novel osteosynthesis plate for the ulnar coronoid process.

BACKGROUND: The present study aimed to biomechanically evaluate a novel locking plate intended for osteosynthesis of coronoid fracture compared to mini L-plates and cannulated screws. METHODS: Biomechanical tests were performed on a fracture model in synthetic bones. Three groups, each with eight implant-bone-constructs, were analyzed in quasi-static and dynamic tests. Finally, samples were tested destructively for maximum strength. RESULTS: The mean (SD) highest stiffness was measured for the novel plate [693 (18) N/mm], followed by the mini L-plate [646 (37) N/mm] and the cannulated screws [249 (113) N/mm]. During the cycling testing of the novel plate and the mini L-plate, no failures occurred, although three of the eight samples of cannulated screws failed during the test. The mean (SD) maximum strength during the destructive testing was 1333 (234) N for the novel plate, 1338 (227) N for the mini-L-plate and 459 (56) N for the cannulated screws. No statistical differences were found during the destructive testing between the two plates (p = 0.999), although statistical differences were found between both plates and the cannulated screws (p = 0.000 each). CONCLUSIONS: Osteosynthesis of the coronoid process using the novel plate is mechanically similar to the mini L-plate. Both plates were superior to osteosynthesis with cannulated screws.

Biomechanical testing of a new plate system for the distal humerus compared to two well-established implants.

PURPOSE: A biomechanical study was performed to test the hypothesis that a new anatomically preformed, thinner, soft-tissue protecting plate system for distal humeral fractures (Tifix®-hybridplate [HP]) would show comparable results in the quasi-static and dynamic testings compared to two conventional implants: The 3.5-mm reconstruction plate (RP) providing primary stability with normal bone mineral density (BMD), and a multidirectional locking plate (Tifix(®)-plate [P]) which can be used with poor bone quality. METHODS: The Tifix(®)-HP was developed by the working group. The biomechanical testing was performed on a C2-fracture-model in 24 synthetic humeri. Three groups, each with eight bone-implant-constructs, were analysed in quasi-static and dynamic tests. RESULTS: The quasi-static measurements showed that under extension loading both locking plates (Tifix(®)-P, Tifix(®)-HP) were significantly stiffer than the reconstruction plate, and that the Tifix(®)-HP had a significantly lower stiffness than the two other implants under flexion loading. In the dynamic tests the Tifix(®)-P allowed significantly less fracture motion compared to the Tifix(®)-HP and the reconstruction plate. In an osteopaenic bone model locking plates failed only under much higher dynamic force than the reconstruction plate. The reconstruction plate and the Tifix(®)-P always failed through screw loosening, whereas the newly developed Tifix(®)-HP showed screw loosening in only one third of cases. CONCLUSION: The hypothesis that the newly designed plate system showed comparable results in the quasi-static and dynamic tests compared to the conventional implants with a significantly lower implant volume and thickness was confirmed.