Biomechanics of four techniques for fixation of the four-part humeral head fracture

OBJECTIVE To carry out a biomechanical study of four techniques for fixation of four-part humeral head fractures. METHODS The fracture was reproduced in 40 plastic humeri, divided into groups of ten according to the fixation technique, each one employing different fixation resources, in different configurations. The humeral models were mounted on an aluminum scapula, with leather straps simulating the rotator cuff tendons, and submitted to bending and torsion tests in a universal testing machine, using relative stiffness as an evaluation parameter. Assemblies with intact humeri were analyzed for comparison. RESULTS The biomechanical behavior of the fixation techniques varied within a wide range, where the assemblies including the DCP plate and the 4.5mm diameter screws were significantly more rigid than the assemblies with the Kirschner wires and the 3.5mm diameter screws. CONCLUSION The four fixation techniques were able to bear loads compatible with the physiological demand, but those with higher relative stiffness should be preferred for clinical application. LABORATORY INVESTIGATION .