Imaging Case of the Week 76

This 30 year old punched an object and heard a ‘click’ sound in his wrist following the episode. The following x-rays belong to the patient; what can you see?

Wrist x-ray

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Right wrist lateral

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The xrays show no fracture around the wrist. The main abnormality is the ‘Terry Thomas Sign’ with widened scapholunate interval to 4.5 mm (normal scapholunate distance should be about 2-3 mm), which is indicative of scapholunate dissociation.

The Terry Thomas sign is usually accompanied by a signet ring appearance of the scaphoid due to its foreshortening. But radial deviation (as above) or flexion of the wrist can also give the scaphoid a signet ring appearance.

The following MRI from the same patient is a T2 fat suppressed sequence showing widening of the scapholunate gap.

T2 weighted MRI slice

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Scapholunate dissociation is an injury that can be commonly misinterpreted as a sprained wrist. This injury needs splinting of the wrist and a referral to hand surgeons.