What causes the Terry-Thomas sign on wrist radiographs
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The Terry-Thomas sign is caused by scapholunate ligament disruption, leading to scapholunate dissociation. This imaging modality, specifically anteroposterior (AP) radiographs, reveals an abnormal separation of the scaphoid and lunate bones following trauma such as a fall onto an outstretched hand (FOOSH). The underlying pathology is a ligamentous injury that results in rotary subluxation of the scaphoid, carpal instability, and potential wrist dysfunction if untreated.
Why is it called so?
It is named after the British comedian Terry-Thomas, who had a distinctive large gap between his two front teeth. The widened scapholunate interval on the wrist radiograph resembles this dental diastema, thus the name Terry-Thomas sign was coined with permission from the actor.
Pathophysiology
The scapholunate ligament normally stabilizes the scaphoid and lunate, maintaining a narrow interosseous space (<2 mm). When the ligament ruptures, the scaphoid tends to rotate dorsally and subluxate, widening the scapholunate gap beyond 3–4 mm on AP imaging. This mechanical derangement produces the characteristic radiographic gap and progressive carpal instability, and may lead to degenerative changes if left uncorrected.
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