Figure 46—1. Posteroanterior (PA) radiograph of the small finger shows a lateral dislocation of the proximal interphalangeal (PIP) joint. The proximal and middle phalanges are both in the same plane, suggesting that there is not a major rotatory component to the dislocation.
Radiographic examination of the laterally dislocated proximal interphalangeal joint is sufficient to diagnose this injury. Depending on the plane of the radiograph, however, confusion between the true lateral dislocation and the volar rotatory dislocation is relatively common. This distinction is important because the extensor mechanism is disrupted in the volar rotatory dislocation as the head of the proximal phalanx protrudes through the triangular ligament between the lateral band and central slip. The rotatory component of the volar dislocation can be suggested on plain x-rays if one view of the digit shows a true lateral of the proximal phalanx with an oblique radiograph of the middle phalanx (Fig. 46—2). This can help the practitioner to distinguish between these injuries. In the straight lateral dislocation, the extensor mechanism may or may not be injured.
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