The use of twin-ring Ilizarov external fixator constructs: application and biomechanical proof-of principle with possible clinical indications

Abstract

Background: In peri- or intra-articular fractures of the tibia or femur, the presence of short metaphyseal bone fragments may make the application of an Ilizarov external fixator (IEF) challenging. In such cases, it may be necessary to bridge the adjacent joint in order to ensure stable fixation. The twin-ring (TR) module of circular external fixation is proposed as an alternative method that avoids joint bridging, without compromising stability of fixation. The aim of this study is to present the experimental tests performed to compare the biomechanical characteristics of the single- and TR IEF modules. The clinical application of the TR module in select patients is also presented and the merits of this technique are discussed.

Methods: In this experimental study, the passive stiffness and stability of the single-ring (SR) and twin-ring (TR) IEF modules were tested under axial and shear loading conditions. In each module, two perpendicular wires on the upper surface and another two wires on the lower surface of the rings were used for fixation of the rings on plastic acetal cylinders simulating long bones.

Results: In axial loading, the main outcome measure was stiffness and the SR module proved stiffer than the TR. In shear loading, the main outcome measure was stability, the TR module proving more stable than the SR.

Discussion: The TR configuration, being stiffer in shear loading, may make joint bridging unnecessary when an IEF is applied. If it is still required, TR frames allow for an earlier discontinuation of bridging; either case is in favour of a successful final outcome.

Conclusion: The application of the TR module has led to satisfactory clinical outcomes and should be considered as an alternative in select trauma patients treated with an IEF. Biomechanically, the TR module possesses features which enhance fracture healing and at the same time obviate the need for bridging adjacent joints, thereby significantly reducing patient morbidity.

Figure 1

In a multi-trauma patient treated with circular external fixator, the TR configuration was applied for the fixation of a) a right open, supracondylar femoral fracture and b) a left distal tibial (pilon) fracture (a). Both were high-energy injuries, resulting in severe fracture comminution and segmental bone loss from the femur at the accident site (b). Bridging of the right knee and left ankle joints was deemed necessary. Subsequently, the femoral fracture was grafted and internally fixed (c, d).

Figure 2

In the patient of Figure 1, the twin-ring configuration allowed for earlier discontinuation of bridging of the ankle joint (e, f, g) during the healing period and faster joint mobilization at follow-up (h, i, j, k).

Figure 3

A Schatzker type VI tibial plateau fracture treated with an Ilizarov frame featuring a twin-ring proximally in order to stabilize adequately the fracture and allow the knee joint to be mobilized as soon as possible. The congruity of the joint line has been restored.

Figure 4

Proximal tibial osteotomy for early-onset osteoarthritis in a 48-year-old woman. A circular frame featuring a proximal twin-ring module was used for fixation. Stable fixation of the proximal tibial fragment with the use of the twin-ring module allowed for early mobilization of the knee joint.

Figure 5

A twin-ring module used in a circular frame for fixation of a distal tibial fracture. The fracture line in these injuries frequently extends to the ankle joint, and the injury becomes a pilon fracture.

Figure 6

The axial loading (AX) configuration was implemented with the plane of single- and twin-ring specimens horizontal.

Figure 7

The shear loading (SH) configuration was implemented with the plane of single- and twin-ring specimens vertical.

Figure 8

For all axial loading tests, comparative graph of load vs. displacement.

Figure 9

For all shear loading tests, comparative graph of load vs. displacement.