Presentation
History
The typical history for a wrist dislocation is one of an athlete who has fallen on an outstretched hand to break a fall or who has mistimed a landing, as in gymnastics. [9] The patient usually presents with vague wrist pain and the sensation of clicks or clunks. Patients may also complain of decreased grip strength with minimal pain. Localized pain is sometimes reported.
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Physical
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Localized tenderness, especially over the dorsoradial aspect of the wrist, may be revealed. The tenderness is worse with dorsiflexion.
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Crepitus or a click with movement and apprehension with radial or ulnar deviation are signals of instability.
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A positive ballottement test result is suggestive of wrist dislocation. To perform the ballottement test, the physician grasps the lunate between the index finger and the thumb of one hand and the triquetrum with the other hand. Volar and dorsal (forward and backward) laxity, crepitus, and pain yield a positive test finding. [9]
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To perform a volar and dorsal shift test, the physician stabilizes the patient's forearm with one hand and volarly and dorsally translates the patient's wrist with the other. Volar subluxation at the midcarpal joint is normal, whereas dorsal subluxation indicates scapholunate instability. [5]
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Tenderness in the anatomic snuffbox can indicate a carpal etiology of pain, although it more reliably suggests a scaphoid fracture.
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A decrease in grip strength may also be seen in patients with wrist injury.
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Median nerve symptoms may be present as a result of volar displacement of carpal bones into the carpal tunnel. [10]
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Lunate dislocation can cause volar swelling on the median nerve. This swelling causes a decrease in 2-point discrimination in the median nerve distribution due to acute carpal tunnel syndrome. Patients with lunate dislocations often prefer to hold their fingers in partial flexion because they have pain on active and passive extension. [6]
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Perilunate dislocation can appear with considerable swelling. A miniature "dinner-fork" deformity is often present, which is produced by dorsal displacement of the distal fracture fragments. The edge of the capitate may be palpable if the swelling is not profound.
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Scapholunate dislocation usually presents with a minimal amount of swelling, and pain is localized over the dorsal scapholunate region. Pain is increased by dorsiflexion. Tenderness over the scaphoid tuberosity may also be present. [6]
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Causes
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Repeated stress on carpal ligaments renders them more prone to injury, especially in athletes.
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The carpal bones serve as a link between the hands and the upper body; a great deal of force is transmitted through them.
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Sports with increased force vectors (height and speed), such as adult in-line skaters and football players, [11] commonly experience such injuries. Other examples of risks are falls from a height; these occur in athletes such as gymnasts, among others.
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Although high energy is the most common cause of injury, some reports describe low-energy trauma as the cause of carpal dislocation. [12]
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Media Gallery
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Lunate dislocation. Posteroanterior projection of the wrist showing the pie shape of the lunate.
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Perilunate dislocation. On the posteroanterior radiograph, crowding is evident between the proximal and distal carpal bones.
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Perilunate dislocation. The lunate is in a normal anatomic position with respect to the radius. The rest of the carpal bones are displaced dorsally.
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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.
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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.
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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.
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