Abstract
Locking of the thumb metacarpophalangeal joint is a relatively rare condition. We report successful treatment in 11 cases of locking of the thumb. Ten patients were diagnosed at an average of 3.2 days (range: 0–21 days) from the injury onset, whereas one patient was diagnosed at 4 months from the injury. Seven of 11 cases underwent successful manual reduction, whereas the other four cases required surgical treatment. Among the surgically treated cases, all cases had a sharp prominent of the radial condyle of the metacarpal head. Therefore, this case series showed 1 chronic case and 4 of 10 cases with a nonround shape of metacarpal heads requiring open reduction.
Keywords: locking of the thumb, metacarpal head, open reduction
Introduction
Locking of the thumb metacarpophalangeal (MP) joint is relatively rare and has been seldom reported. Hyperextension on the thumb MP joint causes locking then flexion is restricted after the locking. During hyperextension of the MP joint, the radial sesamoid bone is moved and locked at the distal and radial side of the metacarpal head. In the treatment of the locking of the thumb, closed reduction should be initially attempted. However, some cases need open reduction. 1 Thus, the risk factor of open reduction is unclear. We describe a case series of 11 patients with locking of the MP joint of the thumb and assess the risk factor of surgical treatment.
Case Series and Results
Patients
From January 2010 to July 2015, 11 patients were diagnosed with locking of the MP joint of the thumb and treated by closed or open reduction. There were six male and five female patients. The mean age of the patients was 26 years (range: 4–71 years). All patients complained of restriction of active and passive flexion after the thumb was hyperextended (average of 4degrees in extension). Ten patients were diagnosed at an average of 3.2 days (range: 0–21 days) from the injury onset, whereas one patient was diagnosed at 4 months from the injury. Patient data are summarized in Table 1 .
Table 1. Summary of individual patient data.
| Case | Age | Sex | Location | Situation | Duration to diagnosis from onset (days) | Reduction | Recurrence |
|---|---|---|---|---|---|---|---|
| Abbreviations: F, female; M, male. | |||||||
| 1 | 4 | M | R | Dodge ball | 0 | Close | No |
| 2 | 5 | M | R | Dodge ball | 0 | Close | No |
| 3 | 23 | F | R | Massage | 3 | Close | No |
| 4 | 27 | M | L | Base ball | 0 | Close | No |
| 5 | 15 | F | L | Massage | 4 | Close | No |
| 6 | 23 | M | R | Basketball | 1 | Close | No |
| 7 | 21 | M | L | Baseball | 1 | Open | No |
| 8 | 11 | M | R | Dodge ball | 1 | Open | No |
| 9 | 46 | F | L | Trauma | 120 | Open | No |
| 10 | 71 | F | R | Trauma | 21 | Close | No |
| 11 | 20 | F | R | Rock climbing | 1 | Open | No |
Radiological Findings
All patients underwent radiography or computed tomography (CT) on initial consultation. According to the radiographic classification of the metacarpal head described by Inoue and Tsuboi (flat, intermediate, and round types), 2 only 1 patient had a round-type metacarpal head and 10 had an intermediate-type metacarpal head. Among the 10 patients with intermediate type, 4 were required to undergo open reduction.
Treatment
In all patients, closed reduction under local anesthesia was performed after diagnosis. The MP joint is first hyperextended by holding the proximal phalanges of the thumb. Thereafter, the joint was passively flexed firmly under axial pressure with radial and ulnar deviations. After reduction was performed successfully, locking was released with clear snapping, and the patient was able to flex the joint immediately after the procedure. Seven of 11 patients underwent successful manual reduction, and a dorsal splint was applied for 2 weeks.
In the remaining four patients, closed reduction failed and surgical treatment under general anesthesia was subsequently performed. Among the four patients, three had an acute case and one had a chronic case. Locking was released by dissecting the accessory ligament and shaving the protrusion of the radial condyle of the metacarpal head. In chronic cases, dissection of the MP joint from the adhesive tissue was additionally required. Postoperatively, an extension-block splint was used for 2 weeks in all patients. There was no recurrence during the follow-up period (range: 4–20 weeks; average: 9.4 weeks) in all patients. At the final visit, the mean MP joint extension was 14.5 degrees and flexion was 87 degrees.
Representative Case
Case 1
A 27-year-old man hyperextended his left thumb during a baseball game and visited the clinic 2 days after the injury ( Fig. 1A ). Lateral view of radiographs showed hyperextension of the MP joint and widening of the dorsal joint space ( Fig. 2A ). Three-dimensional (3D) CT showed a sesamoid bone located distal to the metacarpal head ( Fig. 2B ). Closed reduction was performed with an injection of 1% lidocaine into the MP joint. After passive flexion of the MP joint under an axial compression force, locking was released. A dorsal extension-block splint was used for 2 weeks after reduction. At 3 months after the injury, no instability or pain in the MP joint was noted.
Fig. 1.
( A ) Appearance of the thumb before the reduction. ( B ) Appearance of the thumb in a resting position after the reduction.
Fig. 2.
( A ) Lateral view of X-ray before the closed reduction. ( B ) Three-dimensional computed tomography (CT) of the thumb metacarpophalangeal joint before the reduction.
Case 2
A 20-year-old woman passively hyperextended her right thumb during rock climbing and visited our institution 1 day after the injury. A 3D CT scan showed a sesamoid bone entrapped on the prominent of the radial condyle of the metacarpal head ( Fig. 3A ). Closed reduction with an injection of lidocaine into the joint failed. Thus, an open reduction was performed. A 2-cm longitudinal incision was made on the radial side of the MP joint. The radial accessory collateral ligament was not injured. The radial sesamoid bone was entrapped on the prominent of the radial condyle ( Fig. 3B ). Locking was released by dissecting the accessory ligament and shaving the protrusion of the radial condyle of the metacarpal head ( Fig. 3C ). Postoperatively, an extension-block splint was used for 2 weeks. The patient was encouraged to start active flexion of the MP joint on the second postoperative day. A 3D CT scan at 2 weeks postoperatively showed that the sesamoid bone and metacarpal head were located in the normal anatomical position ( Fig. 3D ). Three months postoperatively, the patient was able to extend (30 degrees) the MP joint of the thumb and flex (80 degrees) without any pain.
Fig. 3.
( A ) Three-dimensional computed tomography (CT) of the thumb metacarpophalangeal (MP) joint before the reduction. ( B ) Intraoperative findings before the reduction ( white arrow represents radial sesamoid bone, black arrow represents the radial side protrusion of the metacarpal head). ( C ) Intraoperative findings after the reduction. ( D ) Three-dimensional CT of the thumb MP joint after the reduction.
Discussion
Locking of the MP joint of the thumb is caused by a hyperextension force at the MP joint. In the clinical situation, locking is often misdiagnosed as a sprain or subluxation due to the rarity of injury and the absence of specific signs in radiographs.
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. 6 Kojima et al analyzed the relationship between the volar plate, sesamoid bone, and collateral ligament in a fresh cadaver to elucidate the mechanism of locking. In their study, incarceration of the sesamoid bone into the joint space is impossible from the anatomical point of view. 5 They concluded that incarceration of the proximal volar plate was the main factor in locking of the thumb. In contrast, the displacement of the sesamoid bone due to rupture of the ipsilateral accessory collateral ligament was reported as a cause of locking of the thumb. 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. First, the membranous lesion of the proximal volar plate is injured due to hyperextension of the MP joint. Then, the constricting bundle rides on the radial side protrusion of the metacarpal head. Finally, incarceration of the proximal end of the volar plate into the joint space causes locking of the MP joint of the thumb. 8 Inoue and Tsuboi reported that the shape of the metacarpal head should be considered in the pathology of locking. 2 They verified seven cases of locking of the MP joint of the thumb on lateral-view radiographs and classified the shape of the metacarpal head into three types: round, intermediate, and flat. They hypothesized that malformation of the metacarpal head (flat type) caused the sharpening of volar protrusion of the metacarpal head, and the protrusion injured the membranous lesion of the volar plate. They concluded that the intermediate- and flat-type metacarpal heads likely cause locking of the MP joint of the thumb compared with the round-type metacarpal head. In this series, the round-type metacarpal head only represented one case. The four cases that required open reduction were all intermediate types. This case series supports the hypothesis that malformation of the metacarpal head might be a risk factor of locking of the thumb.
The treatment of locking of the MP joint of the thumb is controversial. Kojima et al reported that nonsurgical reduction was possible regardless of the time after the injury. 5 In contrast, Yamanaka et al verified 23 cases of locking and reported that manual reduction was successful in 7 patients, but the other 16 required open reduction. 8 In our study, 3 of 10 fresh cases required open reduction. All patients requiring open reduction had an intermediate-type metacarpal head and large protrusion of the radial condyle. Additionally, one patient requiring open reduction had a chronic case that was diagnosed 4 months from the injury onset. No previous studies evaluated the chronic case of locking of the MP joint of the thumb. The shape of the radial condyle of the metacarpal head has anatomical variations. 8 In the locking of the MP joint of the thumb, CT scan revealed a large protrusion of the radial condyle. 9 Form these facts, we speculate that the nonround shape of the metacarpal head with large protrusion of the radial condyle could be a risk factor in the need for open reduction.
Therefore, this case series showed 1 chronic case and 4 of 10 cases with a nonround shape of metacarpal heads requiring open reduction.
Funding Statement
Funding None.
Footnotes
Conflict of Interest None declared.
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