Fractures of the distal radius and ulna

Fractures of the distal radius and/or ulna account for approximately three quarters of bony injuries of the wrist. The radius articulates directly with the carpal bones; the ulna has attachments to the triangular fibrocartilage, which is interposed between the distal ulna and the triquetrum in the proximal row of carpal bones. The radius and ulna themselves articulate at the DRUJ, about which occurs the movements of supination and pronation at the wrist. They are enveloped in a common joint capsule and share multiple ligamentous attachments. Along the midshaft of both bones is the interosseus membrane. Several muscle groups attach on the distal aspect of both bones and contribute to the displacement of fracture fragments.

Extension fractures of the distal radius

Multiple classification schemes have been developed for extension injuries of the distal radius. These tend to be complex and cumbersome. In general, however, the greater the degree of displacement and comminution, the more severe the injury. Extension of a fracture into the radiocarpal or the DRUJ is also a marker for a more severe injury. More complex fractures tend to be more unstable.

Extension fractures result from a fall on an outstretched pronated hand with the impact on the palm and subsequent forced dorsiflexion or hyperextension. On striking a hard surface, the hand becomes fixed while the momentum of the body produces the following 2 forces:

• Twisting force that causes excessive supination of the forearm

• Compression force that acts vertically through the carpus to the radius

The lunate acts as the apex of a wedge against the articular surface of the radius and causes injuries that vary by the age of the patient. Very young children usually sustain a greenstick fracture of the distal radius, with or without an associated fracture of the distal ulna. In adolescents, the lower epiphysis separates, with dorsal displacement or crushing. In adults, fracture occurs within 1 inch of the carpus. The distal fragment usually is displaced upward and backward. In all age groups, the fracture may be complicated by injury to the median nerve or the sensory branch of the radial nerve and/or by fracture of the scaphoid or dislocation of the lunate.

If a concomitant supinating force is applied, often the distal ulna also fractures. Approximately 60% of distal radius fractures are associated with fracture of the ulnar styloid. Approximately 60% of ulnar styloid fractures also have an associated fracture of the ulnar neck.

Colles fracture is the most common extension fracture pattern. The term classically is used to describe a fracture through the distal metaphysis approximately 4 centimeters proximal to the articular surface of the radius. However, now the term tends to be used loosely to describe any fracture of the distal radius, with or without involvement of the ulna, that has dorsal displacement of the fracture fragments.

Colles fractures occur in all age groups, although certain patterns follow an age distribution. In the elderly, because of the relatively weaker cortex, the fracture is more often extraarticular. Younger individuals tend to require a relatively higher energy force to cause the fracture and tend to have more complex intraarticular fractures. In children with open physes, an equivalent fracture is the epiphyseal slip. This is a Salter I or II fracture with the deforming forces directed through the weaker epiphyseal plate.