Terry Thomas is a famous British comedian known for his iconic gap between his front teeth.
In wrist injuries, there is a type of injury whose radiographic appearance resembles Terry Thomas's tooth gap. Frankel referred to this as the "Terry Thomas sign," also known as the "sparse tooth gap sign."
Radiographic Appearance:When there is scapholunate dissociation and tearing of the scapholunate interosseous ligament, the anteroposterior view of the wrist or the coronal view on CT shows an increased gap between the scaphoid and lunate bones, resembling a sparse tooth gap.
Sign Analysis:Scapholunate dissociation is the most common type of wrist instability, also known as scaphoid rotary subluxation. It is typically caused by a combination of extension, ulnar deviation, and supination forces applied to the ulnar palmar side of the wrist, resulting in the rupture of ligaments that stabilize the proximal pole of the scaphoid, leading to separation between the scaphoid and lunate bones. The radial collateral ligament and radioscaphocapitate ligament may also be torn.
Repetitive activities, gripping and rotational injuries, congenital ligament laxity, and negative ulnar variance are also associated with scapholunate dissociation.
Imaging Examination:X-ray (with bilateral comparison):
1. Scapholunate gap > 2mm is suspicious for dissociation; if > 5mm, it can be diagnosed.
2. Scaphoid cortical ring sign, with the distance between the lower border of the ring and the proximal joint surface of the scaphoid being < 7mm.
3. Scaphoid shortening.
4. Increased scapholunate angle: Normally, it is 45-60°; a radiolunate angle > 20° indicates Dorsal Intercalated Segment Instability (DISI).
5. Palmar "V" sign: On a normal lateral view of the wrist, the palmar edges of the metacarpal and radial bones form a "C" shape. When there is abnormal flexion of the scaphoid, its palmar edge intersects with the palmar edge of the radial styloid, forming a "V" shape.
Post time: Jun-29-2024
