Locking metacarpophalangeal joint of the thumb

Pathoanatomy and treatment modifications of metacarpophalangeal joint locking of the thumb

Ten patients with metacarpophalangeal joint locking of the thumb were studied. Three of them underwent surgical release. During surgery, it was found that the radial sesamoid was seated in a cartilage defect on the volar aspect of the metacarpal head. It appeared that the defect was created by the proximal edge of sesamoid. When the abductor pollicis brevis and flexor pollicis brevis muscles were partially detached from their insertion at the base of the proximal phalanx, the locking could be successfully released. We hypothesize the mechanism of the metacarpophalangeal joint locking of the thumb in our cases was a hyperextension injury that displaced the radial sesamoid distally and radially. In turn, the sesamoid's pointed proximal edge wore a groove in the cartilage on the metacarpal head, and under abductor pollicis brevis and flexor pollicis brevis tension, the radial sesamoid was locked into the cartilage defect; thereby causing locking of the joint.

Locked Metacarpo-Phalangeal Joint of the Thumb

16 patients developed locking of the M.P. joint of the thumb as the result of a hyperextension injury. Four were successfully treated by manipulation under an intra-articular injection of a local anaesthetic, while the remaining twelve required open reduction. All were examined 4 to 48 months after treatment (average 12 months).

The torn palmar plate and the accessory collateral ligament, which acted as a constrictive band, were trapped on the prominence of the radial condyle of the metacarpal. Four of the twelve surgically-treated patients had a deformity which we believe was congential: a transverse groove over the radial condyle of the metacarpal.

No patients had a recurrence of the locked joint.

Causes of locking metacarpophalangeal joint of the thumb and its non-operative treatment

The non-operative method of reduction of locking metacarpophalangeal joint of the thumb is described, and illustrated by four case reports. Experimental studies in the hands of a fresh cadaver are also described. Locking of the metacarpophalangeal joint of the thumb can be produced by slight external forces, insufficient to damage strong tissues. Incarceration of the sesamoid bone is anatomically impossible, but incarceration of the proximal portion of the volar plate is believed to be the true cause. This incarceration can be reduced easily by our non-operative method along with intra-articular injection of local anaesthetics.