In this study two different types of forearm internal fracture fixations were compared: limited-contact dynamic compression (DC) plates and fluted intramedullary (IM) rods. Eight matched pairs of intact forearms, consisting of the distal part of the humerus, elbow joint, radius, ulna, interosseus membrane, wrist joint, and metacarpals, were randomly separated into two groups. Each was placed into a custom-designed apparatus and subjected to medial bending, supination, pronation, axial compression, and distraction loading. Loads were applied by a materials testing system, and angular displacements were measured by inclinometers. The procedure consisted of first testing specimens intact, then retesting after osteotomizing and fixing the radius with either a plate or rod in half of the group and retesting after osteotomizing and fixing the ulna in the other half. Testing was continued by osteotomizing and 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 stability in bending and torsion than does the radius. Therefore, if the radius is fractured but the ulna remains intact, IM rodding will produce constructs with greater stiffnesses, particularly in torsion, than if the ulna is fractured and the radius is intact. In the case of a two-bone fracture, implantation of rods will result in a construct with significantly less stiffness in torsion, as well as distraction and compression (in the case of a fracture gap), than if the fractures were plated.(ABSTRACT TRUNCATED AT 250 WORDS)