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Surgical Pearls

Eight Wires/10 Steps: The Siddiqui Method For Applying Static Circular External Fixation

Circular external fixation, also known as Ilizarov frames, has been widely utilized in musculoskeletal surgery since Ilizarov developed a novel frame construct incorporating circular rings with wire fixation.1 Evolving over the years, the circular external fixation frame construct is a useful method of fixation and stabilization for a variety of lower extremity pathologies, segmental bone defects, deformity correction, fracture management and wound offloading. In comparison to internal fixation, a circular external fixation device allows the surgeon to avoid areas of infection, manage soft tissue defects, facilitate weightbearing and manage multiple levels of deformity.

In podiatric surgery, one may use circular external fixation for acquired, congenital, traumatic and post-traumatic conditions, Charcot, and many others. Surgeons apply a majority of these devices in a “static” fashion. A static frame is one that suspends the foot and ankle circumferentially through the use of fixation rings (full or half) with wires and/or half pins. A static frame has many applications but one can modify this device to compress/distract joints of the ankle and foot, offload internal fixation, and suspend wounds/grafts. However, there is wide variation in the application of static frames despite common usage in a multitude of settings. 

When considering the use of external fixation in one’s practice, it is necessary to understand the cross-sectional anatomy of the tibia, fibula, ankle and levels of the foot. Well-defined safe zones exist for the placement of wires and half-pins when applying external circular frames (see the above graphics).3 Equally important is having a thorough understanding of the biomechanics of a circular external fixator. A recent article by Samchukov and colleagues reviews the basics of an external fixation frame, including building a stable construct, proper wire or half pin placement, and angulation and appropriate tensioning based on the anatomic location in the lower extremity.4 Understanding these basic biomechanical parameters is imperative for successful application of a stable frame that is able to protect patients while withstanding rotation, shear and axial loads.5  

One of the reported benefits of circular fixation is the ability to apply a device in numerous ways. However, this can lead to some anxiety and inconsistency when learning how to apply the device. The goal of this column is to provide a stepwise approach to applying a circular frame. This “Eight Wires/10 Steps” approach is the senior author’s recommendation to simplify the application of the circular frame and decrease the intimidation associated with these devices.

Basic Considerations In Circular Frame Placement 

There are some considerations surgeons should be aware of when placing wires.  One should place all wires through the skin and directly to bone while avoiding major neurological and vascular structures. When it comes to wire advancement, the surgeon should cool the wire with wet saline gauze to prevent thermal necrosis of bone. One should aim to place two points of fixation (wires or half pins) per ring (above and below). 

Finally, though it is preferable to always have the wires in direct contact with the rings after a wire transfixes a bone segment, this may not always be the case. In such instances, if the surgeon cannot tension the wire directly to the ring, he or she should build up to the wire appropriately with washers and posts for better wire purchase, thus decreasing the likelihood of wire irritation/breakage.

Step 1: Positioning 

Patient positioning is critical in any surgery and is no less important in applying a circular frame. In order to ensure appropriate positioning and draping of the patient’s lower extremity, there are a couple of key points to keep in mind.

  • The heel should be one fist distance from the end of the operating table with the patella facing forward. One can often accomplish this with the placement of a small ipsilateral hip bump (see photo above).   
  • There should be sterile preparation of the entire lower extremity from the digits to the proximal thigh. This allows for surgical drape placement, sterile tourniquet application and full range of motion of the knee during frame application. 

Step 2: Fixation Of The Foot Ring

When employing an appropriately sized and pre-built static frame, slide the pre-made frame block onto the lower extremity, place it above the ankle, and out of the way.  

Wire 1: Place a 1.8 mm smooth Ilizarov wire in a transverse manner from medial to lateral in the posterior one-third of the calcaneus in order to protect the patient from neurovascular injury. Fixate the transverse wire to the inferior aspect of the foot plate with fixation bolts and center the plate on the foot to allow for circumferential soft tissue clearance. Tension the wire to 90 kg with a tensiometer.     

Step 3: Fixation Of The Forefoot

Wire 2: Place a 1.8 mm smooth Ilizarov wire in a transverse fashion across the forefoot. Start at the medial aspect of the first metatarsal metaphyseal-diaphyseal junction and capture as many metatarsals (first, second and maybe third) while aiming for the fifth metatarsal. Fix the wire to the top of the foot ring so the forefoot remains parallel to the plantar surface of the ring, allowing for adequate soft tissue clearance. One can then tension the forefoot wire to 50 to 70 kg. 

Step 4: Fixation Of The Proximal Tibial Ring 

The tibial block typically consists of two rings between 15 and 20 cm apart. The distal ring is approximately five to seven cm above the ankle joint. Place a small bump behind the knee to slightly flex the knee joint.  

Wire 3: Place a 1.8 mm smooth Ilizarov wire in a transverse manner on the superior aspect of the most proximal ring from lateral to medial. Verify via fluoroscopy that the wire is midline on the proximal tibia. This will ensure bicortical wire purchase. One can fixate the wire to the medial side directly onto the ring or utilize washers if the wire does not lay on the ring. (Technical tip: Resist the urge to bend the wire to the ring if it is off the ring.) Ensure there are two fingerbreadths width circumferentially between the frame and the soft tissue. Tension the wire to 130 kg. 

Step 5: Fixation Of The Distal Tibial Ring

Wire 4: Place a 1.8 mm smooth Ilizarov wire in a transverse fashion from lateral to medial on the inferior aspect of the distal ring as this will make placement of the next wire on this ring easier. Tension the wire to 130 kg.

Step 6: Oblique Wire Fixation Of The Calcaneus

Wire 5: Place an oblique smooth 1.8 mm calcaneal wire on the superior aspect of the foot ring. The wire placement is medial to the insertion of the Achilles tendon and exists around the level of the calcaneocuboid joint. This enables the wire to capture a significant amount of the calcaneus prior to its exit on the lateral aspect of the foot. The angle between wire 5 and the previously placed transverse calcaneal wire (wire 1) should be between 45 and 60 degrees. Tension the wire to 90 kg.

Step 7: Oblique Wire Fixation Of The Tibia 

Wire 6: Place a 1.8 mm smooth Ilizarov wire bicortically on the inferior aspect of the proximal tibial ring. Start on the posterior medial border of the tibia and aim to exit anterolaterally, just lateral to the tibial crest. This will serve as the proximal medial face wire. The angle between wire 6 and the proximal axial tibial wire (wire 3) should be between 45 and 60 degrees. After securing the wire to the frame, one can tension this wire to 130 kg. 

The surgeon can use a medial face half pin here instead of another smooth wire if he or she prefers to utilize a hybrid Ilizarov wire and half-pin construct. When using a half pin, hydroxyapatite-coated half pins are encouraged. One can insert the half-pin after pre-drilling for the appropriately sized pin and placing it off a three- or four- hole post from the anteromedial aspect of the tibia.4 

Step 8: Distal Tibial Oblique Wire Fixation

Wire 7: The surgeon would place another 1.8 mm smooth Ilizarov wire on the superior aspect of the ankle ring (distal tibial ring). Begin on the posterior medial border of the tibia and aim anterolaterally toward the lateral face of the tibia. Once the wire is secure to the frame, tension it to 130 kg. One can place a medial tibial half-pin just medial to the anterior tibial tendon as an alternative.

Step 9: Foot Oblique Wire Fixation

Wire 8: Place an obliquely-oriented 1.8 mm smooth Ilizarov wire on the inferior aspect of the foot ring. Start the wire on the base/tuberosity of fifth metatarsal. Advance the wire obliquely toward the first metatarsal midshaft. This wire may exit dorsal or plantar to the foot ring, and one can tension it between 50 to 70 kg. 

Step 10: Additional Fixation

After the placement of four transverse wires and four oblique wires, the external fixator will appear very stable and the foot will be well positioned circumferentially within the device (see the above photos). The surgeon, at his or her discretion, can add fixation elements to the construct of the frame to improve stability or rigidity. A common location for fixation is the talus and fibula at the ankle. The talus will accept placement of transverse and oblique talar wires. One may place an additional fibular wire, which is commonly known as a tib-fib wire.

In Conclusion

The application of a lower extremity circular external fixation frame can be simplified into a stepwise approach. The “Eight Wires/10 Steps” method can simplify the technical aspects of frame application for students, residents, fellows and junior/senior attendings who are looking to gain more experience in theplacement of a circular external fixation device. 

With additional experience, surgeons can modify the sequence described above to their individual preferences. By following the above steps, with utilization of anatomic safe zones and a basic biomechanical knowledge of external fixation, the foot and ankle surgeon can execute frame application accurately and safely for his or her patients. 

Dr. Mayer is a Clinical Fellow with the Deformity Correction and Orthoplastics Fellowship at the Rubin Institute for Advanced Orthopedics/International Center for Limb Lengthening in Baltimore. 

Dr. Siddiqui is the Director of Podiatric Surgery and the Deformity Correction and Orthoplastics Fellowship at the Rubin Institute for Advanced Orthopedics/International Center for Limb Lengthening in Baltimore. 

Surgical Pearls
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By Brittany E. Mayer, DPM and Noman A. Siddiqui, DPM, MHA
References

1. Ilizarov GA. The principles of the Ilizarov method. Bull Hosp Jt Dis Orthop Inst. 1988;48(1):1-11.

2. Bliven EK, Greinwald M, Hacki S, Augat P. External fixation of the lower extremities: Biomechanical perspective and recent innovations. Injury. 2019;50(1):S10-S17.

3. Catagni MA and Maiocchi AB (eds). Atlas for the insertion of transosseous wires and half-pins: Ilizarov method. 2nd ed. Milan, Italy:Medi Surgical Video;2003.

4. Samchukov ML, Clifford CE, McCann KM, Cherkashin AM, Hutchinson B, Pierce WA. Biomechanical considerations in foot and ankle circular external fixation: maintenance of wire tension. Clin Podiatr Med Surg. 2018;35(4):443-455.

5. Siddiqui NA. Foot and ankle: essential tips, techniques and pearls. In: Herzenberg, JE (ed). The Art of Limb Alignment: Taylor Spatial Frame. Baltimore:Rubin Institute for Advanced Orthopedics;2018:233-256.

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