Dynamic External Fixator Combined with Volar Locking Plate Fixation for the Treatment of AO Type C3 Distal Radius Fractures

Background: AO type C3 distal radius fracture (DRF) is the most difficult-to-treat fracture type because of a tendency to shorten and collapse. The purpose of this study is to investigate the clinical and radiographic outcomes of comminuted intra-articular DRFs treated with a dynamic external fixator combined with a volar locking plate (VLP). Methods: Eleven patients (mean age, 61 years) with comminuted intra-articular DRFs were treated with a dynamic type of external fixator combined with a VLP. Following reduction and fixation with a VLP, the dynamic external fixator was applied and the distal ball joint of the fixator was aligned with the lunate-capitate line. The ball joint was unlocked approximately 2 weeks after surgery to allow wrist mobilization. The fixator was removed 3 - 6 weeks (mean, 5 weeks) after surgery. Consequently, clinical and radiographic assessments were carried out at the final follow-up. Results: At the final follow-up, the mean range values of wrist extension and flexion were 76˚ and 64˚, respectively. Compared with the contralateral side, the mean grip strength was 84%. The mean Modified Mayo Wrist Score and the Disabilities of the Arm, Shoulder and Hand score were 88 and 9, respectively. No significant differences in the radiographic parameters exist between after surgery and final follow-up. Conclusions: This study indicated that the dynamic wrist fixator combined with a VLP is effective for the treatment of AO type C3 DRFs.


Introduction
Distal radius fracture (DRF) is the most common fracture of the upper extremity with high prevalence rates reported worldwide [1] [2] [3]. Traditionally, DRFs were treated conservatively with closed reduction and casting [4]. However, recent reports describe an increasing trend toward surgical treatment including external fixation (EF), percutaneous pinning, and open reduction and internal fixation [5] [6]. An increase in the use of internal fixation for DRF treatment has been noted since the introduction of the volar locking plate (VLP) system in 2000 [1].
AO type C3 DRF is the most difficult fracture type to maintain reduction and fixation because it tends to shorten and collapse [7] [8]. Some of the unstable AO type C3 DRFs cannot be treated with a single-plate system although fixation of the DRF with a VLP provides sufficient stability with minimal reduction loss [9] [10].
The transarticular external fixator, based on ligamentotaxis, is a versatile and useful option for complex DRF treatment [11]. In 1993, Pennig introduced the dynamic transarticular external fixator, which has a double-ball joint to permit a substantial degree of freedom and wrist mobilization after unlocking one ball joint [12] [13] [14].
Although there have been some reports that describe external fixator combined with percutaneous Kirschner wires or fragment-specific fixation for the treatment of DRFs [15] [16] [17], few reports are available on a combination of external fixator and VLP.
The purpose of this study is to evaluate the clinical and radiographic outcomes of AO type C3 DRFs treated with a transarticular dynamic external fixator combined with a VLP.

Methods
This study was approved by the medical research ethics committee at Teine Keijinkai Hospital.

Patient Demographics
The senior author treated 11 consecutive patients (four males and seven females) with comminuted intra-articular fractures of the distal radius (AO type C3 DRFs) with the use of a transarticular dynamic-type external fixator combined with a VLP at Teine Keijinkai Hospital between 2014 and 2017. Their mean age at the time of surgery was 61 years (range, 31 -85 years). The mechanism of injury included falling from standing (seven patients), falling from height (two patients), and a motor vehicle accident (two patients; Table 1). Selection criteria included 1) osteoporotic AO type C3 DRFs that were judged inadequate to be treated with a single-plate system, or 2) unstable AO type C3 DRFs that were caused by high-energy injuries and estimated to be difficult to maintain the length of the radius. After a pneumatic tourniquet was applied, a small incision was made distal to the base of the second metacarpal bone, and a bone screw was inserted into the bone from the radial side. Another small incision was made 15 mm distal to the first incision, and the second bone screw was inserted using a guide sleeve in the same manner. An approximately 3 cm longitudinal incision was made to insert bone screws to the shaft of the radius from the radial side. Moreover, the periosteum was elevated, and two bone screws were inserted using a guide sleeve with the extensor carpi radialis longus tendon retracted dorsally and the brachioradialis muscle to the palmar side. These screws should be at a minimum distance of 3 -4 cm from the most proximal fracture line. An approximately 5 cm longitudinal incision along the flexor carpi radialis (FCR) tendon was then made at the palmar side of the distal forearm, and the FCR tendon and median nerve were retracted to the ulnar side. The pronator quadratus was exposed and detached from its radial side to provide good exposure of the palmar side of the fractured distal radius. Consequently, the fracture was fixed with the VLP after satisfactory reduction was obtained. The external fixator could be applied for the distal radius distraction during the reduction and fixation of the fracture. After wound closure, the external fixator was applied from the radial side, and the distal ball joint of the fixator was aligned with the lunate-capitate line (so-called center of rotation of the wrist) to allow extension-flexion exercise after the unlocking of the joint ( Figure 1). The ball joints of the fixator were locked for approximately 2 weeks postoperatively.
Additional splinting was not provided, and physical therapy was started on the first postoperative day by hand therapists. The distal ball joint of the fixator was unlocked, and wrist joint exercise using the transarticular fixator was allowed. The fixator was removed 3 -6 weeks (mean, 5 weeks) after surgery.

Outcome Assessment
The were quantitatively evaluated with the Modified Mayo Wrist Score (MMWS) [19] for each patient at follow-up. The Japanese Society for Surgery of the Hand version of the Disabilities of the Arm, Shoulder and Hand (DASH) questionnaire [20] served to assess each patient's subjective outcomes at follow-up. This is a 1 -5 scoring system in which the results are transformed into a 0 -100 scale, with a higher score indicating a greater disability.
Plain anteroposterior and lateral wrist radiographs were used for radiographic assessment, which includes the ulnar variance and radial inclination (anteroposterior view) and the palmar tilt (lateral view). All measurements were made by the senior author.

Statistical Analysis
All data are represented as mean ± standard deviation. Statistical comparisons

Results
The injury resulted from a lower-energy mechanism in seven female patients (mean age, 70 years) with osteoporotic bone. The injury resulted from a high-energy mechanism in four male patients (mean age, 45 years) and two patients had other fractures, including bilateral elbow fracture dislocation in one patient, lumbar fracture in the other patient, rib fractures in two patients. All fractures were completely healed without any major complications (Figure 2). After a mean were 78˚ and 84˚, which were both 94% of the values on the contralateral side.
The mean grip strength was 22 kg, which was 84% of the value on the contralateral side. The mean MMWS and DASH score were 88 and 9, respectively ( Table   2).
The radiographic parameters are shown in Table 3. At the final follow-up, the mean positive ulnar variance, palmar tilt, and radial inclination were 0.8 mm, 6.1˚, and 19.9˚, respectively. No significant differences exist in these radiographic parameters between after surgery and the final follow-up, which indicated that the collapse and redisplacement of the fracture were prevented.

Discussion
The results of the current study show that the dynamic external fixator combined with a VLP is a good option for the treatment of AO type C3 DRF, which is one of the most difficult fracture types to maintain the length of the radius and distal articular surface congruity because of a tendency to shorten and collapse [7] [8]. The external fixator was used as a static fixator for approximately 2 weeks postoperatively. After unlocking the distal ball joint that is in line with the  Values are presented as mean ± standard deviation. No significant differences exist in these radiographic parameters between after surgery and the final follow-up. Konrath and Bahler also reported good results in fragment-specific fixation for unstable DRFs. Moreover, 32% and 20% of the patients experienced sensory disturbances in the distribution of the superficial branch of the radial nerve and required repeat surgery, respectively [26].
EF has been extensively used for treating certain types of unstable DRFs [11] [15] [16]. However, Arora  In 1993, Pennig introduced the dynamic transarticular external fixator, which has a double-ball joint to permit a substantial degree of freedom and wrist mobilization after unlocking one ball joint [12] [13] [14]. While unlocking the distal fixator ball joint, which is aligned with the so-called center of rotation of the wrist (lunate-capitate joint line), the wrist joint is allowed to move with minimal risk of collapse. This was based on the report that described the center of rotation of the wrist during extension-flexion as being close to the proximal cortex of the capitate [28]. Recently, it has been revealed that wrist motion is a combination of wrist flexion/extension and radial/ulnar deviation, colloquially referred to as the dart thrower's motion [29]. Although the ball joint does not exactly simulate the correct functional wrist motion, it could allow the wrist joint to move with minimal risk of collapse.
In this study, EF was used as a static fixator for approximately 2 weeks after surgery and as a dynamic fixator after unlocking the distal ball joint to permit appropriate wrist motion under the traction force. At the final follow-up, the radiographic parameters were not lost, and the ranges of motion of the wrist and forearm were good. Thus, the traction force prevented the collapse of the distal radial articular surface and joint stiffness despite the early active and passive movements.
The limitations of this study include the small number of patients, the retrospective design, and the lack of a control group. A randomized, prospective study of a group treated with the present technique and a control group treated with a VLP alone would be needed. Another limitation of this study is that evaluation bias is possible because the senior author was responsible for all clinical and radiographic measurements.

Conclusion
AO type C3 DRF is the most difficult-to-treat fracture type. Although DRF fixation with a VLP provides sufficient stability with minimal reduction loss, some of the unstable AO type C3 DRFs cannot be treated with a single-plate system.
The current study indicated that the dynamic wrist fixator combined with a VLP is an effective and good option for the treatment of AO type C3 DRFs. Further prospective randomized studies are needed to provide more evidence of the effectiveness of the dynamic external fixator in combination with a VLP for DRF treatment.