Temporary Circular External Fixation for Spanning the Traumatized Ankle Joint.

BACKGROUND

Temporary ankle-spanning circular fixation aims to provide osseous stability while (1) allowing access to and recovery of the traumatized soft-tissue envelope and (2) facilitating safe, comfortable, and clinically relevant cross-sectional imaging for surgical planning. It is most commonly utilized in a "span-scan-plan" treatment strategy in cases of peri-articular fractures around the ankle. Conventional monolateral fixators are prone to morbidity at the half-pin sites in the foot and variation in construct stability. Temporary ankle-spanning circular external fixation of the traumatized ankle joint can mitigate these issues.

DESCRIPTION

A circular external fixator construct is assembled beginning with a single tibial ring that is fixed to the tibia by half-pins that are spread on either side of the ring and forming a "virtual ring block." A foot ring is attached via 2 crossed tensioned fine wires in the calcaneum and a single midfoot fine wire in order to prevent an equinus deformity. The tibial virtual ring block and the foot ring are interconnected by 3 polyaxial "rapid-adjust struts" that are evenly distributed around the limb. The fracture is then reduced, and the polyaxial rapid-adjust struts are locked.

ALTERNATIVES

Numerous constructs have been proposed to optimally immobilize the ankle joint while also allowing limb elevation and access to the ankle for soft-tissue care. A commonly utilized construct is the monolateral "bar-and-clamp" spanning external fixator, which relies on half-pin fixation in the foot that may induce bone lysis, result in pin-site infections, and prevent weight-bearing. Calcaneal half-pins are particularly troublesome and can lead to adjacent lysis, instability, and potential loss of initial reduction as a result of the cancellous bone quality.

RATIONALE

The principal objective of temporary joint-spanning external fixation is to realign the traumatized joint and to maintain this reduction until definitive surgery while facilitating soft-tissue treatment and surgical planning. This strategy forms the first step in the "span-scan-plan" approach to pilon fractures described by Sirkin et al.. Multiple subsequent studies have confirmed the superiority of external fixation over splinting for initial soft-tissue care following distal tibial and ankle trauma.

EXPECTED OUTCOMES

Temporary circular external fixation has been shown to outperform monolateral fixation in terms of both the adequacy of the initial reduction and the maintenance of this reduction. Harrison et al. demonstrated that temporary circular fixation of the traumatized ankle yielded 100% good or excellent initial reduction compared with 91% for monolateral fixation. This initial reduction was also better maintained by circular fixator constructs compared with monolateral ones (96% versus 78%).

IMPORTANT TIPS

Placement and orientation of the rings should take into account the zone of injury, access for orthoplastic procedures, and the maximum length of adjustable struts.Orthogonal frame application allows the best biomechanical environment for stabilization of fracture and/or dislocation of the tibiotalar joint to facilitate soft-tissue care. Care should be taken in the operating room to ensure orthogonal mounting of both the proximal and the distal ring to their respective bone segments.Avoid transverse fine wires in the calcaneus to prevent translation while in the frame; consider the use of tensioned olive wires to further protect against translation.Place the midfoot wire through the base of the metatarsals or along the cuneiforms to maximize fixation.Take care to avoid placing the ankle or forefoot in equinus.

ACRONYMS AND ABBREVIATIONS

CEF = circular external fixatorPAD = pronation adductionPER = pronation external rotationSAD = supination adductionSER = supination external rotation.