Carpal instabilities and secondary degenerative changes due to lesions of the radiocarpal ligament complex

Rotational subluxation of the scaphoid (RSS) and ulnar translocation of the carpus (UT) result from distinct lesions of the radiocarpal ligament complex. Trauma, rheumatoid arthritis, calcium pyrophosphate dihydrate crystal deposition (CPDD) and neurologic disease can lead to this ligament defect. The radiological features are identical despite different etiologies of the ligament failure. The secondary degenerative changes in RSS develop in three stages: starting with osteoarthritis at the styloid process, then progression of the degeneration into the mid-carpal joint from central towards ulnar. This mechanism is identical in posttraumatic, inflammatory, neurogenic or CPDD related instability. In cases with rheumatoid arthritis related instability, RSS and UT can be found simultaneously. The knowledge of these radiological features can be helpful in clarifying reasons for carpal changes and in determining the time of onset of the primary ligament failure.