Acute dislocation of the thumb carpometacarpal (CMC) joint is a rare, high-energy injury because of the strong capsulo-ligamentous complex structure. There are a few reports of this injury in the literature, and its optimal treatment remains controversial. Closed reduction and casting, closed or open reduction and percutaneous pinning, and open reduction and ligament reconstruction have been reported, some instability was found on follow up     . The anterior oblique ligament was considered as a key stabilizer of the thumb CMC joint for many years  . However, Strauch et al.  found that the dorsoradial ligament was the primary restraint to dorsal dislocation in their cadaveric studies. Recently, some authors have introduced repair of the dorsal ligament using suture anchors based on the findings     . The purpose of the study was to present our surgical procedures and evaluate the clinical outcome after repair of the dorsal capsulo-ligamentous complex using suture anchors.
Eight consecutive male patients (mean age, 39.8 years; range, 23 - 56 years) with unstable dorsal dislocation of the thumb CMC joint were treated between 2008 and 2018 in our hospital (Table 1). All acute traumatic dislocations of the thumb were immediately reduced, but the dorsal joint instability was recognized grossly. The ruptured dorsal capsulo-ligamentous complex was repaired using suture anchors in all patients, and the joint was immobilized with a 1.8-mm Kirschner wire (K-wire) pinning and splint for 3 weeks. For one patient, 1.8-mm suture anchors (Mitek Mini anchor suture; Depuy-Synthes) were used, and, for the remaining seven patients, 1.0-mm soft anchors (JuggerKnot soft anchor 1.0 mm Mini 2 - 0; Zimmer-Biomet) were used. The mean follow-up period was 10.7 months (range, 6 - 18 months). The grip strength was expressed as a percentage of the grip strength of the uninjured hand. In the grip strength analyses of right-handed patients, 10% was added to the left-side grip strength to compensate for hand dominance  . The range of motion (ROM) of the thumb CMC
Table 1. Summary of the cases.
joint was measured in both the injured and the uninjured extremities with a goniometer, and the degree of volar and radial abduction was expressed as a percentage of the ROM of the uninjured joint. The clinical outcome was retrospectively assessed by measuring the Japanese Society for Surgery of the Hand version of the Quick Disability of the Arm, Shoulder, and Hand (Q-DASH-JSSH) score. Q-DASH-JSSH score is cross-culturally adapted and consists of an 11 items for self-assessment  .
3. Surgical Technique
Surgery was performed with the patient under general anesthesia or brachial nerve plexus block by using an image intensifier. The thumb CMC joint was exposed by a dorsal approach or a modified Wagner’s approach with a 4-cm curved skin incision. First, the abductor pollicis longus tendon was identified and retracted on the volar side. We found that the dorsal capsulo-ligamentous complex was ruptured in all patients. In seven patients, the dorsal capsulo-ligamentous complex was ruptured from the base of the first metacarpal bone, and, in the remaining one patient, it was ruptured from the trapezium. The dorsal capsulo-ligamentous complex had a strong and thick structure (Figure 1). The complex was repaired using two suture anchors after joint reduction (Figure 2). The thumb CMC joint was immobilized with a 1.8-mm K-wire pinning and splint for 3 weeks. The K-wire was removed at 3 weeks, followed by mild active and passive mobilization, and hard labor was prohibited for 2 months.
Figure 1. Intraoperative photograph showing avulsed dorsal capsule-ligamentous complex from the base of the right first metacarpal bone.
Figure 2. The dorsal capsule-ligamentous complex was repaired with suture anchors.
The mean volar abduction of the thumb CMC joint was 66˚ (93.5% for the uninjured hand), and the mean radial abduction was 63˚ (94.2% for the uninjured hand). The mean Q-DASH-JSSH score was 4.8 (range, 0 - 15.6). The mean grip strength of the injured hand was 93.3% of that in the uninjured hand (Table 2). There were no cases of infection, radial superficial nerve or volar thenar median nerve branch disturbance, or early osteoarthritis. Anatomical reduction of the thumb CMC joint was observed in seven patients at the final follow-up. However, in a rugby football player, we found subluxation of the thumb CMC joint at 12 months of follow-up due to reinjury while playing rugby. In this patient, anatomical reduction was observed at 6months of follow-up.
5. Case Presentation
A 30-year-old man presented after a 4-m fall from a ladder and reported left thumb pain. He was right-handed and worked as a planter. Anteroposterior and lateral hand radiographs showed an isolated dorsal dislocation of the thumb CMC joint (Figure 3). No fracture signs were identified by computed tomography. The dislocation of the thumb was immediately reduced, but fluoroscopic examination revealed gross instability of the thumb CMC joint. Surgery was recommended based on the patient’s age and joint stability. Rupture of the dorsal capsulo-ligamentous complex from the base of the first metacarpal bone was observed. We repaired the dorsal capsulo-ligamentous complex using two soft anchors. Radiographs showed anatomical reduction of the thumb CMC joint at 12 months of follow-up (Figure 4). The volar abduction of the thumb CMC joint
Table 2. Clinical outcome.
Figure 3. Preoperative radiograph of the thumb carpometacarpal joint showing an isolated dorsal dislocation.
Figure 4. Postoperative radiograph of the thumb carpometacarpal joint showing good joint congruency.
was 65˚, and the radial abduction was 70˚. The Q-DASH-JSSH score was 4.5. The patient currently has no thumb pain and has returned to his previous work.
The thumb CMC joint is a saddle joint that is concave and convex on each side of the joint. The capsulo-ligamentous complex plays the principal role in providing stability due to the unique anatomy of the joint. Therefore, we must consider different treatment strategies than those for other digit joints. Eaton and Littler  considered the anterior oblique ligament as a key stabilizer of the joint that prevents dorsoradial subluxation of the thumb metacarpal. Therefore, they proposed reconstruction of the anterior oblique ligament, also known as the volar beak ligament. However, Strauch et al.  found that the dorsoradial ligament was the primary restraint to dorsal dislocation. In their cadaveric studies, the greatest degree of joint subluxation was present when all ligaments were intact and the dorsoradial ligament was sectioned. The least degree of joint subluxation was present when all ligaments of the thumb CMC joint, except the dorsoradial ligament, were sectioned. Ladd et al.  identified seven ligaments of the thumb CMC joint: three dorsal deltoid-shaped ligaments, two volar ligaments, and two ulnar ligaments. The dorsal ligament complex (mean thickness, 1.85 mm) was thicker than the volar ligaments (0.71 mm) and the ulnar ligaments (0.98 mm). Based on this evidence, we have performed dorsal capsulo-ligamentous repair and not volar ligament repair. In our case series, the ruptured dorsal capsulo-ligamentous complex was identified and firmly repaired using suture anchors.
Treatment of the dislocation of the thumb CMC joint has been managed by three strategies  : closed reduction and casting, closed or open reduction and percutaneous pinning, and ligament reconstruction. Watt et al.  reported that closed reduction with casting and percutaneous pinning was applied with variable results in their series of 12 cases. Simonian et al.  reported that early ligament reconstruction resulted in a better outcome than that for closed reduction and pinning in a retrospective comparative study of 17 cases. Some case reports     obtained good results after casting or percutaneous pinning. When the joint is stable after reduction, we agree with the conservative treatment or pinning. However, recurrent dislocation and revision surgery have also been reported after conservative treatment or pinning for gross instability of the thumb CMC joint. Recurrent dislocation and instability can lead to articular degeneration and chronic pain. In our study, all joints had gross instability after closed reduction. Recently some authors     have reported repair of the ligament using suture anchors with more advanced medical devices. The advantages of ligament repair are that it is a simple procedure and is less invasive than ligament reconstruction. In addition, no tendon has to be sacrificed in repair with suture anchors in young and high-demand patients. Ligament reconstruction should be considered in cases of chronic dislocation.
The rugby football player in our study was injured again while playing rugby at 12 months postoperatively, and subluxation of the thumb CMC joint was observed on radiographic examination. The patient did not consent to revision surgery due to minor pain. At 6 months of follow-up, anatomical reduction and good function were observed. The patient understood the risk of reinjury from collision sports and returned to playing rugby football.
The limitations of this study are the small number of patients and the short follow-uptimes. Because the dislocation of the thumb CMC joint is such a rare injury, a large-scale multicenter study should be conducted to obtain evidence for this procedure. We consider that dorsal capsulo-ligamentous repair using suture anchors is a reliable and less-invasive treatment for acute, unstable dislocation of the thumb CMC joint in young patients.
Surgical repair of the dorsal capsulo-ligamentous complex with suture anchors is a reliable and simple treatment for acute unstable dislocation of the thumb CMC joint.
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