12.15 Principles of circular external fixation in trauma

The use of circular external fixators with fine tensioned wires has been extensively developed at the Scientific Centre of Reconstructive Orthopaedics and Traumatology in Kurgan, Russia and is now widely practised around the world.

Circular external fixation is not new. Dickson and Diveley presented their fixator of two arches connected by threaded rods and fixed by tensioned K-wires in 1932. Versatile tensioned-wire fixators were developed in Russia by Florensky, Rodin, and Gudushauri in the 1950s. Ilizarov explored the biomechanical and biologic effects of fine-wire fixation and designed a system of closed ring fixators which allowed dynamic, stable constructs in all planes. It is the ability to vary and control the mechanical properties of the construct which distinguishes circular external fixators from many other bone holding devices.

The ‘ideal external fixation system’ (Box 12.15.1) should allow:

These ‘ideals’ are difficult to achieve with a monolateral fixator but can be produced to varying degrees with even simple circular frame designs. With proper planning a circular frame can allow rehabilitation of the joints with full weight bearing and manipulation of the fracture fragments. Restoration of bone loss can progress within a stable limb segment with little effect on limb function.

The Ilizarov method is established in the management of non-union, limb deformity, and leg lengthening. Primary circular fixation in acute fractures remains controversial. Outcomes of treatment are now clearer with recent studies comparing the Ilizarov method with other techniques.

It is helpful to divide indications into absolute and relative, separating those situations where circular external fixation has major advantages over other treatments and those where it may offer some additional benefits. The following indications are derived from the extensive experience in fracture care at our two institutions.

It should be remembered that articular fractures require accurate joint reduction and rigid fixation to allow healing, early movement, and functional recovery. Early weight bearing is rarely a prerequisite in treatment. External fixation works best when it can be applied without opening the fracture and where good limb alignment and early weight bearing is required. For these reasons, it is advisable to apply internal fixation to articular fractures and reserve the Ilizarov method for non-articular injuries. However, the two techniques can be used together, particularly in the proximal tibia with open reduction and limited internal fixation of the joint surface, combined with stabilization of the ‘reconstructed joint fragments’ on the tibial diaphysis using a circular fixator. This combination reduces soft tissue stripping around the fracture and allows adjustments to limb alignment after fixation.

A new fracture in a bone with a pre-existing deformity (especially shortening) gives an opportunity to treat the fracture with correction of the deformity. Ilizarov fixators allow placement of hinges at the CORA (centre of rotation of angulation) of the deformity with stabilization around the fracture. A corticotomy may be performed if the fracture is distant from the CORA.

When patients present late after fracture it may be difficult to reduce the fracture acutely to an acceptable position. Circular fixation can allow gradual reduction over several days. Similarly, some open injuries can have primary closure of the wound with the fracture shortened or angulated. The length and alignment can be restored gradually after wound healing with a circular frame.

The Taylor Spatial Frame (TSF) has been advocated in this mode. This computer-assisted frame allows multiplanar correction but must be used with all the principles of the Ilizarov method. The computer cannot compensate for poor planning, application, or understanding of the method.

There may be many more relative indications for circular external fixation. The following sections deal with fixation in specific fracture groups.

Few acute upper limb injuries require circular fixators. In the humerus, severe bone loss, infected fractures, extensive highly fragmented fractures, and distal fractures with elbow instability may be relative indications. The Compass Hinge fixator allows protection of elbow ligament reconstructions and complex fracture fixations with a large range of motion. However, it should be noted that the application of a circular frame to the humerus is difficult, requiring extensive knowledge of cross-sectional anatomy.

In our experience there is almost no indication for ring frames in acute fracture of the clavicle, radius, or ulna. The principles of rigid internal fixation with early recovery of joint motion are perhaps best applied to these fractures.

Most diaphyseal femoral fractures can be treated by intramedullary nailing. External fixation has been advocated in those patients who have concomitant severe chest injury, contaminated open fractures, or multifragmentary fractures of the distal segment (knee bridging fixation). The hybrid advanced system of frame application allows stable fixation of the proximal femur without transosseous wires. This has extended the use of circular frames in this region.

Circular frames are useful in the upper femur in bone loss fractures of more than 2cm. We have applied frames to such fractures with extensive soft tissue injury, allowing stable bone fixation with full weight bearing within a few days. Compression–distraction or bone transport may progress in parallel with limb rehabilitation.

Circular fixation may also be employed where intramedullary nailing of a shaft fracture is technically impossible. Fractures occurring below an area of deformity in the proximal femur or adjacent to an implant may be well fixed with a ring frame.

In complete articular fractures of the distal femur, rigid fixation of the articular fragments will give the best joint surface for mobilization. In the elderly, osteoporotic bone stock and deficient soft tissues may make extensive open reduction and internal fixation (ORIF) inappropriate, risking high infection rates and fixation failure. Minimal internal fixation of the femoral condyles combined with circular fixation of complex metaphyseal fractures offers advantages of secure fixation of the joint surface with minimal disruption of the soft tissue envelope around the distal femur.

Infrequently, destruction of the joint surface is such that it is impossible to reconstruct any useful joint. Circular external fixation is perhaps the method of choice for primary arthrodesis of the knee in this situation (Figure 12.15.1). If necessary this may be combined with restoration of limb length via a proximal corticotomy and distraction.

The tibia is unique in that it is easily accessible and has poor subcutaneous tissue cover over much of its length. Open operations may risk deep infection, wound breakdown, and non-union. Most closed and many open diaphyseal fractures are best treated with intramedullary nails but there remains a range of patients and fracture types in which these implants are suboptimal.

Circular fixators are best applied for non-articular fractures at the upper or lower metaphyso-diaphyseal junctions. These can be reduced closed with the fixator. They can be aligned easily and frames allow immediate weight bearing and short times to union. These fractures are often too proximal or distal to nail and plate fixation risks soft tissue complications, even with minimally invasive techniques.

In diaphyseal fractures with extensive fragmentation, circular frames allow excellent stabilization without further soft tissue injury around the tibia (Figure 12.15.2). In open fractures with soft tissue loss and a high-energy fracture pattern a circular frame may be applied with shortening of the limb to allow skin closure followed by gradual distraction after wound healing to restore limb length.

Segmental or complex open tibial fractures in children present fixation challenges. Intramedullary devices are contraindicated with active physes. Circular frame fixation may be used in these cases (Figure 12.15.3). Healing times are short in children, and frames can often be removed within a few weeks.

As stated previously, intra-articular fractures without dissociation from the tibial shaft (Schatzker I–IV) and similar ankle fractures (AO Muller Type B) require reduction and internal fixation. A few undisplaced articular fractures may benefit from circular fixation alone, particularly with poor skin cover.

Bicondylar fractures without joint surface damage (Schatzker V) can be well treated with circular frames applied in a closed manner. Careful reduction in the frontal and sagittal plane is needed. Schatzker VI injuries will usually need open reduction of the joint surface with internal fixation. The circular fixator provides excellent control of the shaft fracture.

Pilon fractures are characterized by comminution of the joint surface including coronal splitting of the plafond (Figure 12.15.4A, B). They require open reduction of the joint surface. Circular external fixation combined with minimal internal fixation provides adequate stabilization for sound bony union (Figure 12.15.4C). In many cases, the ankle joint is bridged with the fixator, distracting the joint, protecting the cartilage and preventing equinus contracture. Once the articular element of the fracture is uniting, the foot extension can be removed and ankle motion started (Figure 12.14.4D).

Circular fixators may look complex but they consist of simple parts which fall into four groups:

Meticulous preoperative planning with the patient and the radiographs is essential. Patients may spend many months in a frame and must fully understand the commitment that is required for a good outcome. If possible, patients should see a typical frame before surgery, appreciate the problems that may arise during treatment, and have access to information and help when problems occur.

It is usually inadvisable to apply a circular fixator for multiple lower-bone fractures or multisystem trauma during the initial surgery for open fractures and life-saving procedures. If a circular frame is indicated, the limb may be temporarily stabilized with a bridging monolateral fixator with later conversion.

A sound knowledge of the cross-sectional anatomy of the limbs is necessary for safe wire placement. Variations in neurovascular anatomy and displacement of structures by fracture must be sought to avoid nerve or vessel injury.

Frame application begins with the insertion of reference wires, usually at the ends of the long bones, under radiographic control. An understanding of the anatomical and biomechanical axes of the limbs allows correct frame orientation on these wires and prevents secondary deformities. Where possible, transosseous wires should be passed far enough away from joints to avoid an intra-articular passage, reducing the chance of septic arthritis.

Rings should be chosen that allow at least 2cm of clearance all around the limb. Very large rings are avoided as they reduce the stability of the frame and are inconvenient.

It is important to tension all fine wires around a circular frame. In general, tensions of 100–130kg are recommended to provide sufficient stability and axial loading.

These constructs are based on the hybrid advanced system (HA system) devised predominantly in Lecco, Italy. It provides variations on the traditional ‘all-wire’ Ilizarov designs, making fixation easier and is better tolerated by patients.

In practice, different frame constructs are used for fractures in the upper, middle, and lower segments of the humerus. The four-ring frame described for middle-third injuries can be modified for specific fractures throughout the bone.

The preassembled frame is composed of a 5/8 ring distally, two intermediate rings and a proximal arch (Figure 12.15.5). One reference wire is inserted distally and one half-pin proximally to align the frame to the humerus. The frame is applied to these and middle-third wires are added avoiding the neurovascular structures as Additional distal wires and half-pins are placed. A modification of this frame may be used for bone segment transport in the treatment of humeral bone loss.

In some fracture patterns, or in obese patients, a variation of this system can be applied using two arches proximally, one intermediate ring, and the distal 5/8 ring (Figure 12.15.6). This frame, although less stable to angular motion, is tolerated better by patients.

The standard assembly incorporates a full ring distally, an arch proximally at the subtrochanteric level and one or two intermediate rings depending on the type and level of the fracture. Fixation distally includes a transverse reference wire and two half-pins. Proximal fixation is achieved by attaching two half-pins to the arch as shown. At the intermediate ring or rings, olive wires have traditionally been used to reduce and hold the fracture fragments in alignment. Transosseous wires in the mid-thigh are poorly tolerated by patients for the duration of treatment. Half-pins may be substituted, entering the thigh posterior to the iliotibial band.

The proximal section consists of one 90-degree and one 120-degree arch. It should be secured to the two-ring distal section by oblique support connectors. The proximal arch should be at the greater trochanter and the distal arch is at least 2.5cm proximal to the fracture. The distal ring is located at the base of the femoral condyles and the proximal ring is 2.5cm distal to the fracture (Figure 12.15.7).

The first reference wire is inserted at the base of the condyles in a transcondylar manner from lateral to medial and perpendicular to the anatomical axis of the femur. After placement of this wire, rotation must be checked. The proximal half-pin is inserted from posterolateral, at the level of the greater trochanter. During attachment of the half-pin to the arch, the frame must remain centred on the thigh. Wires and/or olive wires are then utilized to reduce the fracture. Reduction is confirmed with the aid of a C-arm image intensifier in both planes. After reduction, the remaining half-pins and wires are inserted as shown (Figure 12.15.7). Wires used for reduction, which are in a position which might cause irritation or pain, should now be removed.

This frame consists of four levels constructed to allow 5–6cm between the upper and lower sections, giving an unobstructed radiographic view of the fracture (Figure 12.15.8).

The frame is aligned as before. The proximal arch and distal ring are secured as before. The two central rings are fixed with lateral half-pins and tensioned wires passing from posterolateral to anteromedial, exiting anterior to the femoral artery.

A similar frame can be used for the distal segment, concentrating the three rings around the fracture (Figure 12.15.9). The two distal rings are connected with hexagonal sockets measuring 2, 3, or 4 cm, depending on the length of the distal fragment.

A variation is needed when the distal fragment is small and there is not enough space for two rings below the fracture. In this case a single distal ring is used, fixed as before but the frame is continued across the knee to include a ring at the proximal and distal tibial metaphysis. The femoral and tibial sections can be connected with hinges to allow some knee motion.

There are many variations in frame design for complex tibial fractures or intra-articular fractures but the following description provides a basic system for the commonest indications.

The preassembled frame consists of one ring above and below the metaphyseal fracture and a single ring on the distal tibia (Figure 12.15.10). The intra-articular component of the injury must be reduced anatomically. When there is no displacement, the frame can be applied without open reduction. Periarticular fragments may be secured with screws or olive wires.

After joint reduction, two reference wires are passed transversely through the proximal and distal tibia perpendicular to the anatomical axis of the bone. The frame is aligned and further fixation is achieved with a second wire distally, passing through the fibula and tibia. The central ring is fixed with a single wire passing from anterolateral to posteromedial, avoiding the bulk of the muscles and a half-pin perpendicular to the subcutaneous surface of the tibia. Fixation on the proximal ring is completed with two olive wires on either side of the reference wire. The position of these wires can be varied depending on the fracture configuration. A similar frame may be used for metaphyseal fractures without joint involvement, especially in those with osteoporotic bone.

A four- or five-ring frame will be needed depending on the fragmentation of the fracture (Figure 12.15.11).

Two reference wires are inserted as before and frame alignment is checked. Tibial length is then restored with gentle distraction, aiding reduction. Olive wires may be inserted to reduce the central fragments. After complete reduction, stability is improved with anteromedial half-pins and perpendicular wires where possible and a distal fibular wire.

Circular external fixation provides stabilization of the metaphyseal component of the injury after open reduction of the joint. The preconstructed frame consists of two rings for the tibia, connected to a foot frame with threaded rods, and an intermediate ring at the level of the tibiofibular syndesmosis (Figure 12.15.12).

The proximal section is fixed to the tibia as described earlier. The foot frame is fixed with two olive wires in the heel and two wires in the forefoot. Distraction is performed between the tibial section and the foot frame, causing ligamentotaxis (Figure 12.15.13). The fracture is openly reduced, restoring the joint anatomy perfectly. The fracture fragments are further stabilized with bone grafts, olive wires, or screws. After wound closure, the intermediate ring and wires are applied at the level of the fracture for further stabilization (Figure 12.15.12). Distraction is maintained between the foot and tibia, off-loading the articular cartilage. Distraction is removed after 1 month and the connecting rods are substituted with hinges, allowing ankle motion. At 6 weeks, the foot frame is removed and progressive weight bearing is begun until fracture union.

Recovery of limb function is the primary goal of fracture care. The patient must be fully involved in the rehabilitation with education and encouragement. Passive and active joint motion begins on the day after surgery. This will require adequate analgesia and supervision with a physiotherapist. Resting splints for neighbouring joints (especially the ankle) will prevent contractures.

For intra-articular fractures, weight bearing may be delayed for several weeks but otherwise early loading will enhance fracture healing and reduce the time spent in the fixator.

The fixator must be regularly checked (initially weekly) to detect loss of wire tension or deformation of rods. Loose or broken wires will become painful and predispose to pin-site infection. If adjustments are being made for compression, lengthening, or angular corrections then patients should be encouraged to make the adjustments themselves. This promotes acceptance of the frame and integration into the normal activities of daily living.

Pin-site care is mandatory. Minor problems with wires and half-pins are common but major pin sepsis can be avoided with good care. The Oxford protocol is available at: http://www.noc.nhs.uk/limbreconstruction/information/pin-site-care.aspx

When union is complete, the fixator can be removed. In children this should be done with a brief general anaesthetic, but in adults sedation and analgesia will suffice. It is not recommended to transfer limbs from a circular frame to a cast in order to shorten the fixator time as this negates the benefits of early joint rehabilitation. After removal the patient must be reviewed with radiographs of the region as late deformity or refracture may occur with premature frame removal.