A BIOMECHANICAL COMPARISON OF 2 METHODS OF FIXATION OF FRACTURES OF THE FOREARM

In this study two different types of forearm internal fracture fixatio ns were compared: limited-contact dynamic compression (DC) plates and fluted intramedullary (IM) rods. Eight matched pairs of intact forearm s, consisting of the distal part of the humerus, elbow joint, radius, ulna, interosseus membrane, wrist joint, and metacarpals, were randoml y separated into two groups. Each was placed into a custom-designed ap paratus and subjected to medial bending, supination, pronation, axial compression, and distraction loading. Loads were applied by a material s testing system, and angular displacements were measured by inclinome ters. The procedure consisted of first testing specimens intact, then retesting after oseotomizing and fixing the radius with either a plate or rod in half of the group and retesting after oseotomizing and fixi ng the ulna in the other half. Testing was continued by osteotomizing the remaining intact bone to create a two-bone fracture, fixing them, and retesting after creating a 5-mm gap at the osteotomy sites. These tests showed that the intact ulna contributes more to forearm stabilit y in bending and torsion than does the radius. Therefore, if the radiu s is fractured but the ulna remains intact, LM redding will produce co nstructs with greater stiffnesses, particularly in torsion, than if th e ulna is fractured and the radius is intact. In the case of a two-bon e fracture, implantation of rods will result in a construct with signi ficantly less stiffness in torsion, as well as distraction and compres sion (in the case of a fracture gap), than if the fractures were plate d. The torsional stiffness with rod fixation was low with a two-bone f racture (2.23% of intact specimens) compared with fixation with plates (83.4% of intact specimens) and the resistance to distraction and com pression small (5-10 N of axial load). Consideration might be given to supplemental stabilization if IM rods are used in these circumstances .