Pathoanatomy and treatment modifications of metacarpophalangeal joint locking of the thumb

Abstract

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.

Treatment of Locking of the Metacarpophalangeal Joint of the Thumb

“…The pathology of locking is controversial. Previous studies suggested that the pathology of locking is based on the entrapment of the sesamoid bone, 3,4 proximal end of the volar plate, 5 and deformity of the distal metacarpal head. 2 Ueda et al reported a case of locking of the MP joint of the thumb due to an intra-articular loose body.…”

“…7 The tension of the abductor pollicis brevis and flexor pollicis brevis might also contribute to locking since the release of these muscles led to successful reduction of locking. 4 Based on the CT and intraoperative findings, the pathology of locking of the MP joint of the was influenced by several factors such as the sesamoid bone, volar plate, and accessory ligament, so-called "constricting bundle." 8 Yamanaka et al reported that the pathology of locking of the thumb is induced by the following mechanism.…”

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

“…Locking of the thumb metacarpophalangeal (MP) joint refers to a condition that causes a fixed state of the MP joint with a slight hyperextension deformity and motion restriction [1][2][3][4][5]. It can result from relatively minor hyperextension injuries.…”

“…Although there are some controversies, an incarcerated volar plate, accessory collateral ligament, or entrapped radial sesamoid are considered to be possible causes of locking [1,3]. Closed reduction can be attempted initially, but open reduction is often required, particularly when the presentation or diagnosis is delayed [4]. In the absence of clinical information, radial sesamoid movement or entrapment at the 1st MP joint is often overlooked on routine anteroposterior and lateral radiographs because of the bony overlap and variable degree of normal range of motion of the 1st MP joint [6].…”

“…In the absence of clinical information, radial sesamoid movement or entrapment at the 1st MP joint is often overlooked on routine anteroposterior and lateral radiographs because of the bony overlap and variable degree of normal range of motion of the 1st MP joint [6]. Therefore, computed tomography (CT) is preferred for diagnosing a locked thumb to evaluate the location and status of the sesamoid [4,5]. Although CT is an excellent modality to assess bony details, it causes radiation exposure and has a lower accessibility compared to ultrasound (US).…”