As the name goes, scapholunate ligament is a ligament connecting the scaphoid and the lunate.
This ligament keeps both bones stable to one another during flexion and extension of the wrist. It is also a commonly injured ligament in the wrist joint.
The mechanism of injury is a bit similar to that which leads to TFCC injury – fall on the outstretched hand. While TFCC tear yields pain on the pinky side of the wrist, pain caused by scapholunate ligament injury is more central in location.
Terry Thomas Sign
Diagnosis of scapholunate ligament tear is made with thorough clinical examination, xrays and more advanced imaging like MRI. Typically, scapholunate ligament tear will cause the scaphoid to rotate away from the lunate which, on xray, is seen as a gap between scaphoid and lunate. This gap reminds us to the space between two front teeth, like Terry Thomas the actor! However, one must take note that Terry Thomas sign indicates a more advanced and chronic tear. Ideally scapholunate tear should be diagnosed before the occurrence of Terry Thomas sign.
It is not uncommon to detect scapholunate ligament tear while performing arthroscopy for other conditions.
Scapholunate ligament repair is a simple procedure that can be done arthroscopically.
Untreated scapholunate ligament tear will cause instability of the scapholunate articulation. Chronic instability of the scapholunate articulation will eventually cause a pattern of arthritic changes in the wrist joint which we know as SLAC (scapholunate advanced collapse).