Fig. 2From: Ultrasound diagnosis and follow-up of a locked thumb metacarpophalangeal joint caused by radial sesamoid entrapment: a case reportLongitudinal scan of ultrasound on volar surface of the 1st metacarpophalangeal joint shows distal displacement of the radial sesamoid bone (arrow) into the joint space (a). After reduction, the radial sesamoid has relocated to the radial condyle of the metacarpal head (b). P: proximal phalangeal base, MC: metacarpal headBack to article page