Background
Wrist injuries are common among athletes. Emergency physicians and/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.
See the image below.
Perilunate dislocation. The lunate is in a normal anatomic position with respect to the radius. The rest of the carpal bones are displaced dorsally.
For excellent patient education resources, visit eMedicine's Breaks, Fractures, and Dislocations Center. Also, see eMedicine's patient education article, Wrist Injury.
Epidemiology
Frequency
United States
In a study by Larsen and Lauritsen, as many as 2.5% of all emergency department visits were made by patients with wrist injuries. [1] 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. [2]
Kerr and colleagues concluded that dislocation/separation injuries represent a relatively small proportion of all injuries sustained by high school athletes in the United States; however, the severity of these injuries indicates a need for enhanced injury prevention efforts. [3]
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. [2]
Sport-Specific Biomechanics
The mechanism of injury for a wrist dislocation is usually a fall on an outstretched hand (ie, FOOSH injury) that results in a hyperextension type of injury to the wrist. High energy is a common characteristic feature in these injuries. [4] The distal row of carpal bones is commonly 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. [5] 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 (DISI) pattern. DISI normally occurs in unrecognized scaphoid subluxations or scaphoid fractures. The opposite type of deformity is known as the volar intercalated segment instability (VISI) pattern. 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. [6, 7] VISI also is a sign of midcarpal instability or lunotriquetral injury.
Mayfield and coworkers have classified wrist dislocation as follows (see the image below) [8] :
Progressive perilunar instability pattern as reported by Mayfield et al. Stage I involves scaphoid instability; stage II, scaphoid and capitate instability; stage III, scaphoid, capitate, and triquetrum instability; and stage IV, lunate dislocation.
See the list below:
-
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
-
Lunate dislocation. Posteroanterior projection of the wrist showing the pie shape of the lunate.
-
Perilunate dislocation. On the posteroanterior radiograph, crowding is evident between the proximal and distal carpal bones.
-
Perilunate dislocation. The lunate is in a normal anatomic position with respect to the radius. The rest of the carpal bones are displaced dorsally.
-
Scapholunate dislocation. The scapholunate space is usually greater than 4 mm, a scenario also known as the Terry-Thomas sign. Rotation of the scaphoid causes the scaphoid to be viewed end-on, producing the classic signet-ring sign.
-
Progressive perilunar instability pattern as reported by Mayfield et al. Stage I involves scaphoid instability; stage II, scaphoid and capitate instability; stage III, scaphoid, capitate, and triquetrum instability; and stage IV, lunate dislocation.
-
On a normal lateral radiograph, the 4 Cs should be easily visualized. The 4 Cs are the convexity of the distal radius, the convexity and the concavity of the lunate, and the convexity of the capitate. A longitudinal axis aligns the radius, the lunate, the capitate, and the third metacarpal bone. The scapholunate angle is normally 30-60 degrees.
