The patient is positioned supine, often with a support under the hip of the operative leg. The goal is to orient the lower leg perpendicular to the operating table and floor to facilitate proper placement of the external fixator. A sterile proximal calf support (bump) (Fig. 39.1) should be created to suspend the lower leg during external fixator placement. The lower leg is prepared and draped in usual sterile fashion, and the leg is exsanguinated using a tension bandage unless persistent infection is suspected.

The ankle joint is approached using the individual surgeon’s preferred exposure, taking into account prior incisions and the status of the existing soft tissue envelope. We prefer to perform ankle arthrodesis through a direct anterior approach when possible, using the interval between the tibialis anterior (TA) and extensor hallucis longus (EHL) tendons, with preservation of the medial and lateral malleoli. We prefer to preserve the malleoli in most cases, as there is potentially more
surface area available for fusion and less bone loss. In selected cases, resection of one or both malleoli can improve bone contact and/or alignment.

A longitudinal midline incision is made over the anterior ankle, starting approximately 10 cm proximal to the ankle joint and 1 cm lateral to the tibial crest, just along the lateral border of the palpable TA tendon (Fig. 39.2). The incision is extended distally to the talonavicular joint.

Deep, full-thickness retraction is used as soon as possible to limit the risk of skin compromise. We prefer early use of self-retaining retractors (i.e., Gelpi retractors), and at no point, should direct tension be placed on the skin margins. Protect the traversing branch of the superficial peroneal nerve, which is often identifiable as it crosses directly over or immediately proximal to the ankle joint.

The extensor retinaculum is identified and divided directly over the EHL tendon. In our experience, it is imperative to attempt to maintain the integrity of the TA tendon sheath during the approach, in order to minimize risk of anterior wound complications associated with tendon “bowstringing.” The EHL and TA tendons are retracted laterally and medially, respectively, with deep self-retaining retractors. The dissection is continued deep, and the deep anterior neurovascular bundle is identified and safely retracted laterally with the EHL tendon. Incise the anterior joint capsule and periosteum over the distal tibia and dorsal talar neck longitudinally, sharply dissect the
periosteum off the bone, and retract the capsule and periosteum medially and laterally, exposing the ankle joint fully (Fig. 39.3). Visually inspect the ankle joint, removing any loose bodies and anterior tibial or talar osteophytes as necessary.

Once the ankle joint is fully exposed, attention is now turned to meticulous joint preparation. Again, just as with ankle arthrodesis using internal fixation, external fixation does not obviate the need for thorough joint preparation. We routinely use joint distraction with either lamina spreaders or an invasive joint distractor placed over anterior smooth pins in the distal tibia and talar head-neck junction. (Remaining articular cartilage is removed with a sharp elevator, osteotome, or chisel.) We prefer to maintain the architecture of the subchondral bone of the tibial plafond and talar dome, which facilitates easy adjustment of coronal and sagittal plane alignment without compromising limb length or bony apposition. On the contrary, flat cuts sacrifice limb length and make alignment adjustments more challenging. In the setting of malalignment, some deformity correction may need to be made through the joint with limited sacrifice of the subchondral osseous anatomy. The subchondral bone is penetrated with a drill bit and/or narrow chisel (Fig. 39.4). This promotes fusion by increasing surface area, delivering autogenous bone graft to the arthrodesis site, and encouraging bridging trabeculae for fusion. The malleoli are preserved when possible, and the medial and lateral gutters are prepared as described above to further increase the arthrodesis surface area. Autogenous or allograft bone grafting is at the discretion of the individual surgeon, but excessive use of bone graft might prevent bony apposition and should be avoided when possible. In cases of prior infection, we selectively supplement limited bone graft with appropriate antibiotic powder.

Once the joint is prepared, attention is then turned to ankle joint reduction and provisional alignment prior to application of the external fixator. We find that provisional fixation with one or two smooth, large-diameter Steinmann pins is often necessary to maintain ideal position prior to application of the ring external fixator (Fig. 39.5). This pin is placed similar to the guide pin used for retrograde intramedullary TTC nail procedures. Provisional fixation should maintain adequate reduction of the prepared talus within the prepared ankle mortise. Optimal function and potential for fusion is established with maximum contact between the arthrodesis surfaces, avoiding anterior translation of the talus within the ankle mortise. Valgus is generally established in the hindfoot; varus malalignment at the ankle joint must be avoided. Furthermore, calcaneus or equinus positioning must be corrected to a neutral sagittal plane alignment. Finally, the second metatarsal should be in line with the tibial crest to ensure proper rotational positioning, avoiding internal rotation.

The wound is then gently irrigated and meticulously closed in a layered fashion, making sure to reapproximate the extensor retinaculum and subcutaneous skin. The skin is closed in a tensionfree manner, using nonbraided suture. We recommend closing the wound before applying the external fixator because access to the wound becomes challenging with the ring external fixator applied. If the individual surgeon chooses to close the wound after application of the ring external fixator, one or two anterior fixator struts or threaded rods can be retracted or removed to allow adequate access to the wound(s). A deep drain may be used to minimize the risk of hematoma and subsequent wound complications, but it must be positioned so as not to interfere with pin placement. Judicious use of incisional negative pressure wound dressings is at the discretion of the individual surgeon and may have a role in cases of prior infection or tenuous soft tissue envelope.

With any use of external fixation, adherence to safe, proper transosseous wire and half pin placement is quintessential to avoid untoward injury to soft tissues and neurovascular structures at risk. For ankle and TTC arthrodesis, a thorough understanding of cross-sectional anatomy of distal lower extremity is paramount to safe use of transosseous fixation (11). In general, we recommend the use of 1.8-mm thin wires and 5- or 6-mm hydroxyapatite-coated half pins for ankle and TTC external fixator arthrodesis. Threaded half pins should be meticulously placed to ensure that threads
engage the tibia in a bicortical manner. Drilling and placement of half pins should always include use of blunt dissection to bone and use of tissue-protecting guides or sleeves placed against the bone. Saline solution should always be utilized during drilling to prevent thermal bone necrosis.

For the purposes of ankle and TTC arthrodesis, we generally recommend a two-ring proximal tibial block. The top, or proximal-most, ring in the tibial block is generally placed just distal to the midshaft of the tibia. The bottom, or distal-most, ring in the tibial block is generally placed in the distal third of the tibia, proximal to the metaphyseal flare (Fig. 39.6). The tensioned reference wire for the proximal-most ring is placed in a medial-oblique manner or directly perpendicular to the long axis of the tibia, and two half pins are placed directly perpendicular to the medial face of the tibia.