Proposal of a New Dynamic Distraction Device to Treat Complex Periarticular Fractures of the Metacarpophalangeal Joint of Long Finger

Abstract

Background: Complex periarticular fractures of the metacarpophalangeal joint (MCPJ) are often challenging to treat. Conservative and operative treatments are often burdened with stiffness, loss of function, and poor clinical outcome. These phenomena could be a direct consequence of long period of immobilization. To promote a short time of immobilization and a quick return to daily activities, it is mandatory to stabilize the fracture maintaining the active range of motion (AROM) of the ray. A simple solution is to reduce the fragments by means of dynamic ligamentotaxis. The authors propose a new dynamic distraction device (DDD) for the MCPJ. Methods: The DDD for the MCPJ was made of Kirschner wires bent and connected to counteract dislocation forces and to allow mobilization of the joint. The DDD was tested on a cadaver model under a simulated load in physiological conditions, and also in metacarpal and proximal phalanx (P1) fracture patterns. The effectiveness of the device was evaluated under fluoroscopy. Results: The data showed that DDD is able to achieve fracture reduction through ligamentotaxis and primary fragments stability and to avoid secondary dislocation during AROM of complex periarticular fractures of the MCPJ. Conclusions: The frame could be an alternative option to treat periarticular fractures of the MCPJ. The DDD implant has several advantages: It is time efficient because assembly and application take only few minutes. Furthermore, it is very versatile; indeed, it can be used in all metacarpal and phalanx bones, even in the central rays.

Introduction

Periarticular and intra-articular fractures of the metacarpophalangeal joint (MCPJ) are lesions that involve not only bone tissue but also all neighboring structures with potential consequences. The main treatments remain nonsurgical procedures (cast or splinting) or various types of fixation techniques that range from Kirschner wires (K-wires) to plate and screws. However, small fragments fixation could be challenging and a good stability could be difficult to achieve. The treatment often implies immobilization with consequences like scarring, adhesion, and stiffness with poor outcome and compromised global hand function.³,⁶,⁷

To achieve closed reduction and fracture stability using ligamentotaxis, Suzuki et al proposed a simple distraction method to treat interphalangeal joint articular fractures. In particular, the skeletal traction device introduced by Badia et al improved fixation stability with satisfactory functional results.^1,2,4,10

The same principle could be used to treat MCPJ bone injuries. However, the biomechanics of the MCPJ is still not completely clear. Pagowski and Piekarski⁸ proposed a variable center of rotation theory: As the collateral ligaments are inextensible and originate eccentrically, they hypothesized that the axis of rotation is not fixed. However, Youm et al¹¹ disagreed with this hypothesis and proposed a stationary center of rotation placed inside the metacarpal head.

The authors of this article performed a MCPJ kinematic analysis. With aid of fluoroscopy, the kinematic of the MCPJ was analyzed. Two markers were put on metacarpal and phalangeal heads; their motion was first tracked using radiograph and then drawn. It was noticed that the different markers of the phalanx run along parallel tracks with different radius during the movement. The paths of the markers of the phalanx were drawn on paper, and they looked exactly like the metacarpal head profile (Figure 1). These data support the theory of Youm et al¹¹, and the head of the phalanx was used as a marker to draw the curvature of the metacarpal head.

Figure 1.

(a) The different markers of the phalanx run along parallel tracks with different radius during the movement. The paths of the markers of the phalanx were drawn on paper, and they looked exactly like the metacarpal head profile. (b) This curvature allowed a constant distraction during the movement of flexion and extension.

Our aim was to create a device that was easy and fast to apply and could allow immediate active motion of the fractured finger. We believe it is critical to gain immediate active motion instead of a complete range of motion of the injured finger.

Materials and Methods

The Device

The dynamic distraction device (DDD) was made of 4 K-wires (1.4 mm in diameter and standard length). Two K-wires were implanted into the diaphysis crisscrossed until the base. The entry point was extra-articular. The part of the wires that remained out of the skin was bent in dorsal Z shape (Figure 2).

Figure 2.

Surgical technique. The first step is to implant 2 intramedullary crisscrossed Kirschner wires as shown in the scheme (a) under fluoroscopic control (b). The entry point is extra-articular. The part of the wires that remained out of the skin is bent in Z shape (c).

The third K-wire was bent following the flexion curvature of the metacarpal head. The authors planned it using the MCPJ of nonfractured finger (Figure 3). The 2 diaphysial wires were connected to the bent wire with clamps.

Figure 3.

Surgical technique. Placing the nonfractured finger in 3 different positions, the markers are drawn as in the figure (a) (the point 1 is the metacarpophalangeal joint, while points 2, 3, and 4 are drawn considering the proximal interphalangeal joint in different positions). These markers (b) provide the exact curvature to bend a third Kirschner wire following the metacarpal’s head shape (c).

The fourth K-wire was fixed transversely in the proximal phalanx (P1) in the chosen point, parallel to the articular surface of the phalanx (Figure 4). It was placed distally to the fracture (about 5 mm). According to authors, the exact position of the transverse wire could vary, on the basis of fracture pattern and surgeon’s necessity. In fact, the system can be set in different ways just adjusting the position of the connecting clamps and of the transverse wire.

Figure 4.

Surgical technique. The last step is to fix a fourth Kirschner wire (K-wire) transverse to P1. Then the first 3 K-wires are connected with clamps and provide the distraction force applied to the fourth K-wire (a) The aspect of the device at the end of the procedure (b, c).

Experimental Phases

The authors applied the DDD on 3 fresh cadavers hand models studying the device under different conditions.

Group 1 (physiological pattern)

We evaluated the distraction effect of DDD on the MCPJ during the simulated active range of movement (SAROM). The SAROM was performed simulating the action of the flexor digitorum superficialis, the flexor digitorum profundus, and extensor digitorum communis applying traction to their muscular bellies. We constantly balanced the tension between agonist and antagonist tendons, stabilizing the joints of the fingers.

The evaluation was performed in physiological condition and after the frame implant. The joint widening was evaluated by dynamic image fluoroscopy at 0°, 15°, 30°, and 45° of flexion. In all experimental phases, we used a centimeter ruler and a goniometer (NexGen Ergonomics Inc., Pointe Claire, Quebec, Canada).

Group 2 (complex fracture of the base of P1)

The P1 base fracture was performed with ostheotome. The lesion was a transverse volarly angulated fracture with >10° angulation and >2 mm shortening. The fracture extended to the articular surface. We tested the fracture behavior under dynamic imaging fluoroscopy at 0°, 15°, 30°, and 45° of MCPJ flexion before and after the DDD implant.

Group 3 (fractures of the metacarpal neck)

An extra-articular metacarpal neck fracture was performed using an ostheotome on the third finger ray. The fracture was a transverse volarly angulated fracture with >20° angulation and 15° of rotational deformity. The fracture was reduced with Jahss maneuver editing the rotational defect. The osteosynthesis was performed with aid of DDD and the fracture stability was checked during the SAROM using dynamic imaging fluoroscopy (Figure 6).

Figure 6.

Radiological results in the specimen with fracture of the metacarpal neck (a). The joint space is increased after the implant of the distraction device (b), and the reduction of the fracture is maintained (c).

Results

Group 1

During physiological SAROM, the joint space was in average 2.5 mm (min.: 2 mm, max.: 3 mm). After DDD implant, the joint space was restored and the collected data showed that the same width was obtained. The joint space during MCPJ flexion remained in average 2.5 mm (min.: 2 mm, max.: 3 mm) both in physiological condition and after the DDD implant. No rotation defect was found (Table 1).

Table 1.

Radiological Results at Different Degrees of Flexion and Report of Fracture Displacement.

	J-S at 0°	J-S at 15°	J-S at 30°	J-S at 45°
Physiological	3 mm	3 mm	2 mm	2 mm
P1 base fracture	3 mm No displacement	3 mm No displacement	2 mm No displacement	2 mm No displacement
Metacarpal neck fracture	3 mm No displacement	3 mm No displacement	2 mm No displacement	2 mm No displacement

Note. J-S = joint space.

Group 2

Without distraction, the dislocation of the fracture slightly improved at 45°, but not the shortening. Under DDD action, the fracture reduced the angulation (<10°) and regain the physiological length (<1 mm) without any rotational deformity. Furthermore, the fracture gained and maintained stability during all SAROM. The physiological joint space was restored. The DDD was able to restore physiological joint space in presence of P1 base fracture as well (Figure 5).

Figure 5.

Radiological results in the specimen with complex fracture of the base of the first phalanx (a) after the application of the dynamic distraction device. Good alignment is obtained with ligamentotaxis (b), and the reduction is maintained (c) even in flexion (see arrow).

Group 3

The facture stability was achieved and maintained in all planes. Even in this case, the physiological joint space was restored.

Discussion

The treatment of periarticular fractures of MCPJ seems to be a compromise between the need of immobilization and the stiffness that is a result of a long period of immobilization. This is particularly true for the long and central fingers. Ideally, a better system of osteosynthesis should achieve closed bone stabilization without joint immobilization.

In 1999, Hurov and Concanno⁵ proposed a dynamic traction splint to treat MCPJ fractures adapting the frame described by Schenck⁹ for the proximal interphalangeal joint. However, the devices were very bulky, not easy to handle, and hard to produce in large numbers.

In contrast, the DDD is a simple, cheap, and easy handling, and it seems an easy solution to provide a continuous skeletal distraction (0°-45° of flexion) and an active functional range of motion from the thumb to little finger.

In particular, the key point of the device lies in its ability to manage very unstable fractures of the base of the phalanx (comminuted with metaphyseal involvement). The DDD can restore the finger’s kinematic during flexion-extension, balancing the tension forces between muscles and tendons.

Furthermore, the DDD’s easy handling allows to use it in case of multiple finger injury. Even if the neighboring finger is injured, an early active mobilization is possible in order to avoid multiple finger immobilization and stiffness.

Conclusions

This frame could be an alternative option to treat periarticular fractures of the MCPJ. The DDD implant has several attractive features. It is time efficient because assembly and application take less than 15 minutes. It is versatile; indeed, it can be used in all metacarpal and phalanx bones, even in the central rays. Moreover, it requires a very short learning curve. After these encouraging results, the authors advocate to improve the experimental data with clinical studies to evaluate the reliability of the device.