Abstract：Objective To study the mechanism of metacarpophalangeal joint locking of the thumb, and modify the current treatment.Methods Eighteen patients with metacarpophalangeal joint (MCPJ) locking of the thumb were studied from 2007 to 2014 in Beijing Jishuitan Hospital . There were 17 males and 1 female with age of 19-41 years old, and 15 patients were on the right side,3 patients were on the left side. Four patients were treated surgically. According to the anatomical characteristics found in the operation, the mechanism was deduced, Fourteen patients were treated conservatively, including 3 patients treated with modified reduction method and 11 patients treated with traditional reduction method. The patients were followed up to observe the active and passive range of motion(ROM), pain, stability of metacarpophalangeal joint of the thumb, and recurrence.Results (1)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 (APB) and flexor pollicis brevis (FPB) muscles were partially detached from their insertion at the base of the proximal phalanx, the locking could be successfully released. All patients satisfied the recovery of the function. No recurrence of the locking was found during a follow-up of 3 to 6 months. All patients obtained the full active and passive ROM for their MCPJ with neither pain nor instability. Before operation,the mean active and passive ROM of the thumb MCPJ was from -31.8° to -19.3° and from -32.5° to -30°,respectively. The mean ROM of the joint was from -3.8° to 52.5° postoperatively. Active hyperextension of the first metacarpophalangeal joint was restricted after operation. The results of the treatment were assessed as satisfactory by all patients. (2) Fourteen cases were treated with conservative method successfully. Before reduction, the mean active and passive ROM of the thumb MCPJ was from -28.6° to 15.2° and from -30.4° to 26.5°, respectively. All patients obtained the full active and passive ROM for their MCPJ with neither pain nor instability. The mean ROM of the joint was form -15.8° to 47.5°after reduction. No recurrence of the locking was found during a follow-uo of 6 to 8 weeks.Conclusions The pathogenesis of thumb metacarpophalangeal joint dislocation is that the radial sesamoid is displaced distally and radially when the thumb is overextended. A groove-shaped cartilage defect on the articular surface of the metacarpal head is carved by the proximal edge of the radial sesamoid. Under the tension of the APB and FPB tendons,the sesamoid is embedded in the cartilage defect, thereby causing locking of the joint. Based on this mechanism, a modified reduction method can be used to treat MCPJ locking of the thumb.
郜永斌, 熊革, 戴鲁飞, 刘坤. 拇指掌指关节绞锁18例临床分析及发病机制的探讨[J]. 中华解剖与临床杂志, 2020, 25(3): 292-296.
Gao Yongbin, Xiong Ge, Dai Lufei, Liu Kun. Clinical analysis and investigation of mechanism of 18 cases with metacarpophalangeal joint locking of the thumb. Chinese Journal of Anatomy and Clinics, 2020, 25(3): 292-296.
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2020, Vol. 25 
