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Watson's test, also known as the scaphoid shift test, is a diagnostic test for instability between the scaphoid and lunate bones of the wrist. Test procedure [ edit ]
A dynamic scapholunate instability is where the scapholunate ligament is completely ruptured, but secondary scaphoid stabilizers are still preserved; [6] these are the scaphotrapezial (ST), scaphocapitate (SC) and radioscaphocapitate (RSC) ligaments. [6] In a static scapholunate instability, these other ligaments are ruptured as well.
- A line through the long axis of the scaphoid bone. - A line perpendicular to the distal articular surface of the lunate bone. It should normally be 30°-60°. [1] Dorsal intercalated segment instability (DISI) is a deformity of the wrist where the lunate bone angulates to the dorsal side of the hand. [2] [3]
A condition called scapholunate instability can occur when the scapholunate ligament (connecting the scaphoid to the lunate bone) and other surrounding ligaments are disrupted. In this state, the distance between the scaphoid and lunate bones is increased. [1]: 180 One rare disease of the scaphoid is called Preiser's Disease.
Because SLAC results from scapholunate ligament rupture, there is a larger space between the two bones, also known as the Terry Thomas sign. [10] Scaphoid instability due to the ligament rupture can be stactic or dynamic. [11] When the X-ray is diagnostic and there is a convincing Terry Thomas sign it is a static scaphoid instability.
In radiology, the Terry-Thomas sign is a scapholunate ligament dissociation on an anteroposterior view of the wrist. [1] [2] Most commonly a result of a fall on the outstretched hand , the scapholunate ligament ruptures resulting in separation of the lunate and scaphoid bones. This burst causes the scaphoid bone to dorsally rotate. [3]
Scapholunate advanced collapse (also known as SLAC wrist) is a type of wrist osteoarthritis.SLAC wrist is the most common type of post-traumatic wrist osteoarthritis [1] and is often the result of an undiagnosed or untreated scapholunate ligament rupture. [2]
The cavity of the midcarpal joint is very extensive and irregular. The major portion of the cavity is located between the distal surfaces of the scaphoid, lunate, and triquetrum and proximal surfaces of the four bones of the distal row. Proximal prolongations of the cavity occur between the scaphoid and lunate and between the lunate and triquetrum.