Excerpt from Wrist Dislocation

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Background

Wrist injuries are common among athletes. Emergency physicians or family practitioners frequently perform the initial evaluation of wrist injuries and determine the initial treatment. Recognizing wrist dislocations early and properly referring patients with wrist dislocations can prevent complications, including prolonged pain and discomfort, surgery, and lost time from sports participation.

Frequency

United States

In a study by Larsen, as many as 2.5% of all ED visits were made by patients with wrist injuries. A small number of those patients present with wrist dislocations. Subluxations and dislocations account for 10% of carpal injuries, with perilunate dislocation being the most common type of dislocation (Schwartz, 2000).

Functional Anatomy

The wrist joint is composed of distal radial and ulnar surfaces, 8 carpal bones, and the proximal metacarpal bones. The distal carpal row consists of the following bones: hamate, capitate, trapezoid, and trapezium. The proximal row consists of the following bones: scaphoid, lunate, triquetrum, and pisiform. The carpal bones are held together by a complex set of ligaments, including the interosseous, volar, and dorsal ligaments and a triangular fibrocartilage complex (TFC). The dorsal ligaments are weaker than the volar ligaments, making dorsal dislocation more common (Schwartz, 2000).

Sport Specific Biomechanics

The mechanism of injury usually is a fall on an outstretched hand resulting in a hyperextension type of injury to the wrist. High energy is a common characteristic feature in all these injuries (Chun-Ying, 2004). The distal row of carpal bones commonly is displaced dorsal to the proximal row. This displacement occurs as a result of a scaphoid fracture or a scapholunate dislocation, and if the force is severe, a perilunate dislocation occurs (Browner, 1998). Trans-scaphoid perilunate fracture-dislocation is slightly more common than perilunate dislocation.

Different posttraumatic deformity patterns can cause the lunate to lose its linear relationship with the capitate and to tilt dorsally or volarly, resulting in a collapse deformity. The most common collapse deformity is caused by the lunate dorsiflexing on the radius. This is compensated by the capitate flexing volarly. This deformity is also known as the dorsiflexed intercalated segment instability pattern (DISI). DISI normally occurs in unrecognized scaphoid subluxations or scaphoid fractures. The opposite type of deformity is known as volar intercalated segment instability pattern (VISI). Although VISI can be seen in healthy patients with lax ligaments, posttraumatically, it is a result of the lunate flexing volarly on the radius as the capitate tilts dorsally (Lichtman, 1997; Linscheid, 1972). VISI also is a sign of midcarpal instability or lunotriquetral injury.

Mayfield and coworkers have classified wrist dislocation as follows (see Image 5):

• Stage I - Scapholunate dislocation resulting from a tear in the scapholunate interosseous ligament and radiolunate ligament



• Stage II - Lunate-capitate subluxation resulting from injury to the capitolunate joint



• Stage III - Lunate-triquetral dislocation resulting from injury to the triquetrolunate interosseous ligament



• Stage IV - Lunate dislocation resulting from dorsal radiolunate ligament injury

Please click here to view the full topic text: Wrist Dislocation