Early sonographic diagnosis and successful management of the sesamoid bone locking in the thumb

Ultrasound diagnosis and follow-up of a locked thumb metacarpophalangeal joint caused by radial sesamoid entrapment: a case report

Background

A locked thumb metacarpophalangeal joint is a rare condition that presents as restricted joint motions with mild hyperextension deformity, usually after a relatively minor hyperextension injury. Owing to the limitations of radiographs, computed tomography is a useful diagnostic imaging modality for assessing sesamoid displacement. However, despite its convenience, ultrasound findings of the locked thumb have rarely been reported. Here, we report a case of a locked thumb metacarpophalangeal joint diagnosed and followed-up using ultrasound.

Case presentation

A 15-year-old boy with a locked thumb metacarpophalangeal joint presented to our hospital. On physical examination, the 1st metacarpophalangeal joint was found to be hyperextended, and active and passive flexions were not possible. While radiographs were inconclusive, ultrasound revealed radial sesamoid entrapment at the 1st metacarpophalangeal joint causing locking. After closed manual reduction, metacarpophalangeal motions recovered. Success of the reduction was also confirmable by ultrasound.

Conclusions

Ultrasound can be a feasible modality to diagnose a locked thumb metacarpophalangeal joint and immediately judge the success or failure of the reduction.

Locked Thumb Metacarpophalangeal Joint Caused by Entrapment of the Sesamoid Bone: A Report of 2 Cases

Locked thumb metacarpophalangeal joint caused by entrapment of the sesamoid bone is an uncommon entity. The intact volar plate, strong ligamentous attachment between the sesamoid bone and the joint, and altered axis of inserted muscle all contribute to failure of closed reduction. The patient's history, clinical presentation, and plain radiographic findings are all important clues to diagnosing this rare disease. We describe 2 patients with a similar mechanism of injury, where the sesamoid bones were displaced into the thumb metacarpophalangeal joint causing lock thumb. The anatomy, pathophysiology, and surgical management of the patients are also described and discussed. Both patients were successfully treated with meticulous open reduction.