The radius and the ulna lie parallel to each other and are invested at their proximal ends with a relatively large muscle mass. Because of their close proximity, injury forces typically disrupt both bones and their ligamentous attachments. They can be thought of conceptually as two cones lying next to each other pointing in opposite directions (Fig. 13–1).
The radius and the ulna can be conceptualized as two cones that come together at the ends, thus permitting supination and pronation as the radius "rolls" around the ulna.
A fracture of one of the paired forearm bones, especially when angulated or displaced, is usually accompanied by a fracture or dislocation of its "partner."
The bones of the forearm are bound by several essential ligamentous structures (Fig. 13–2). On either end, the joint capsules of the elbow and wrist hold the radius and ulna together. Anterior and posterior radioulnar ligaments further strengthen these attachments proximally. The distal radioulnar joint contains a fibrocartilaginous articular disk that acts as an energy absorber with compressive forces. The third important ligamentous attachment is the interosseous membrane, which provides both longitudinal stability and load transference between the two bones.1
The radius and the ulna are joined together by the capsules at either end of the wrist and elbow joints. The interosseous membrane joins the two bones together throughout the shafts.
Muscle attachments to the forearm bones are important because of their penchant for displacing fracture fragments. Simply speaking, the shafts of the radius and the ulna are surrounded by four primary muscle groups whose pull frequently results in fracture displacement or nullification of an adequate reduction (Fig. 13–3). These groups are as follows:
Proximal: The biceps and the supinator insert on the proximal radius and exert a supinating force.
Midshaft: The pronator teres inserts on the radial shaft and exerts a pronating force.
Distal: Two groups of muscles insert on the distal radius. The pronator quadratus exerts a pronating force. The brachioradialis and abductor pollicis also produce deforming forces, depending on the location of the fracture. Of these, the brachioradialis exerts the predominant displacing force.
The muscle attachments of the forearm act to predict displacement of radius fractures. A. The supinator muscle supinates, the bicep muscle flexes, and the pronator teres and pronator quadratus muscles pronate. A fracture of the proximal radius at location 1 will result in a supinated and flexed proximal fragment and a pronated distal fragment. When the fracture is distal to the pronator teres insertion at location 2, the proximal fragment will be neutral and flexed while the distal fragment is pronated and pulled toward the ulna. ...