A joint is dislocated(1) when the two joint surfaces are no longer in contact with each other (Figure 1). This is to be distinguished from a subluxation(2), when there is some contact of the joint surfaces, but the surfaces are not parallel (Figure 2). This is further distinguished from flexion or extension of the joint, where the joint surfaces may not be in complete contact at the extremes of motion, but they are parallel to each other (Figures 3 and 4). A dislocation or subluxation may be suspected by a visible deformity of a digit, and confirmed by x-ray.
Figure 1. This patient’s radiographs demonstrated dorsal dislocation of the left index finger middle phalanx onto the proximal phalanx. This is most clearly seen on the lateral and oblique views. Image by Catherine Ly, licensed under CC BY-NC-SA 4.0).
Figure 2. This is an example of subluxation. There is some contact of the joint spaces, but they are not parallel, and the axes of the bones are not aligned. Subluxation typically results from a ligament tear or fracture causing the joint to be unstable. Image by Grant Thomson licensed under CC BY-NC-SA 4.0).
Figure 3. This patient presented with a finger stuck in flexion. Initial impression was that it was dislocated. Look carefully at the lateral view (enlarged below). Image by Grant Thomson licensed under CC BY-NC-SA 4.0).
Figure 4. Magnification of the lateral image above demonstrates that the joint surfaces of the PIP joint are parallel, but at the extreme of flexion. There appears to be an old injury to the solar lip of the middle phalanx. This is a flexion contracture, not a dislocation. Image by Grant Thomson licensed under CC BY-NC-SA 4.0).
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[…] DislocationBy Thomson, GrantA joint is dislocated(1) when the two joint surfaces are no longer in contact with each other (Figure 1). This is to be distinguished from a subluxation(2),… Leave a Comment […]
[…] DislocationBy Thomson, GrantA joint is dislocated(1) when the two joint surfaces are no longer in contact with each other (Figure 1). This is to be distinguished from a subluxation(2),… Leave a Comment […]
[…] DislocationBy Thomson, GrantA joint is dislocated(1) when the two joint surfaces are no longer in contact with each other (Figure 1). This is to be distinguished from a subluxation(2),… Leave a Comment […]