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. Distally, radioulnar ligaments from a joint that contains a fibrocartilaginous articular disk. Throughout the midshaft of both bones is a strong interconnecting fibrous interosseous membrane.
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 actions to displace 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:
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. B. The brachioradialis and abductor pollicis longus muscles act to pull distal fragments more proximally, resulting in overriding fragments.
When considering treatment of these fractures, careful attention must be paid to the maintenance of length and alignment. The ulna is a fixed straight bone around which the radius rotates. The radius, to the contrary, has a lateral bow that must be preserved to allow full pronation and supination after healing (Fig. 13–4).1
The lateral bow of the radius must be preserved to allow full pronation and supination to occur.
In this chapter, fractures of the radius and ulnar shaft will be considered. The shafts of the radius and ulna are defined as the diaphyses of the long bones not encompassed by joint capsules or ligaments. The reader is referred to Chapter 12 for a discussion of distal radius fractures, and Chapter 14 for a discussion of fractures of proximal structures such as the radial head, olecranon, and coronoid process. The classification system used in this chapter for radial and ulnar shaft fractures is based on anatomic as well as therapeutic considerations.
Fractures can occur anywhere along the shaft of the radius or ulna. These fractures are divided into three groups: (1) radial shaft fractures, (2) ulnar shaft fractures, and (3) combined radius and ulna fractures. The Monteggia (ulna fracture with radial head dislocation) and Galeazzi (radius fracture with distal radioulnar dislocation) fractures are classified under their respective single bone fractures.
Radial shaft fractures can be divided into proximal, midshaft, and distal fractures (Fig. 13–5). Isolated fractures of the proximal two-thirds of the shaft of the radius are uncommon in adults because this area is well protected by the forearm musculature. Fractures of the distal third are important because they are frequently associated with injury to the radioulnar joint, especially when they are displaced or angulated.
Radial shaft fractures.
The most common mechanism is a direct blow to the radial shaft, most commonly, at the junction of the middle and distal portions of the bone. It is at this point that the radius is least enshrouded by muscle and therefore exposed to a greater amount of direct trauma.
Tenderness is present along the fracture site and can be elicited with direct palpation or longitudinal compression. Galeazzi fracture dislocations should be suspected if wrist tenderness or ulnar head prominence is present.2
Routine anteroposterior (AP) and lateral views of the forearm are ...