terry-thomas sign terry-thomas sign in radiology, the terry-thomas sign is a scapholunate ligament dissociation on an anteroposterior view of the wrist. most commonly a result of a fall on the outstretched hand (foosh), the scapholunate ligament ruptures resulting in separation of the lunate and scaphoid bones. this burst causes the scaphoid bone to dorsally rotate. a gap of more than 3mm is pathognomonic for scapholunate dissociation. terry-thomas signarrow pointing to the gap between scaphoid and lunate bones. its name derives from terry-thomas, who had a similar looking gap between his two front teethdifferential diagnosisscapholunate ligament dissociation the resulting separation between the scaphoid and lunate bones leaves a space on the x-ray that is similar to the gap comedian terry-thomas had between his front teeth. for newer radiology students who do not know who terry-thomas was, this finding might also be known as the david letterman sign.