Complex Ankle and Hindfoot Arthrodesis Using Circular External Fixation
TAKE-HOME POINTS
- Ankle and hindfoot fusion using circular external fixation is a useful surgical technique in patients with diabetes, Charcot, osteomyelitis, deformity, and/or bone and soft tissue compromise in order to obtain solid bony fusion, stable limb alignment, and eradication of infection in cases of complex pathology.
- Deformity correction with osteotomies and meticulous joint preparation is required in order to obtain broad, cancellous bony surfaces for fusion with neutral alignment. Autograft from the distal fibula and/or medial malleolus can be combined with bone allograft to assist with joint fusion.
- The ankle and hindfoot are provisionally pinned into neutral coronal and sagittal alignment through the plantar surface of the foot using large K-wires prior to placement of the lower leg in the center of a circular 3-ring compression frame. Typically, 2 to 3 points of fixation are used per ring with a combination of half-pins and smooth wires.
- Ring attachments are built up or down to the level of the half-pins and wires in order to prevent pins and wires from bending, breaking, or causing iatrogenic deformity during tensioning. Crossing olive wires are used in the midfoot and calcaneus with dual tensioning devices to ensure an even pull on both sides of the foot.
- Dynamic or static compression struts are used to obtain 8 to 10 mm of compression across the ankle and hindfoot, followed by addition of an anterior foot ring to increase construct rigidity. Daily pin care is started 3 to 4 days after surgery and patients are kept non-weight-bearing for approximately 2 months in the frame with a total frame period of 3 to 8 months depending on bony healing on X-ray.
SURGICAL TECHNIQUE
SETUP AND APPROACH
Patients are positioned supine with padding under the operative extremity to achieve neutral leg rotation (Figures 1A-1D). A thigh tourniquet is placed with the foot positioned at the end of the bed and on top of the radiolucent padding to avoid interference of the contralateral leg during lateral X-rays. After sterile prepping and draping, the extremity is exsanguinated above the level of an active infection, and the tourniquet inflated.
For isolated ankle arthrodesis, an anterior or lateral approach can be used, while for TTC arthrodesis, a lateral approach is required to access both the ankle and subtalar joints. A 10-cm longitudinal incision is made along the distal fibula, curving slightly and anteriorly along the distal extent of the incision. Dissection is continued down to bone using full thickness flaps, and the distal fibula is removed 2 to 3 cm above the ankle joint using a saw and osteotome (Figures 2A-2G). The distal fibula can be used subsequently as bone grafts depending on the quality of bone. The peroneal tendons are retracted posteriorly, and dissection is then continued to the posterior facet of the subtalar joint.
JOINT PREPARATION AND ALIGNMENT
Both the anterior and posterior neurovascular bundles are protected along the distal tibia with Hohmann retractors while a saw is used to create flat cuts across the tibial plafond and talus to allow apposition of flat, broad cancellous bony surfaces. Flat cuts followed by later joint compression will often shorten the limb by 2 to 3 cm. This leg length discrepancy can later be accommodated using a shoe lift, as needed. All retained hardware and/or infected and necrotic tissues in the ankle and hindfoot are removed using a rongeur and a pituitary rongeur.
The medial malleolus is osteotomized vertically using a direct medial incision and approach with full thickness flaps, and in line with the previous tibial plafond, is both cut and removed. The medial malleolus can also be used for bone grafts in fusion sites. A smooth-tip lamina spreader is placed in the subtalar joint for distraction and a curved osteotome, curettes, and a small rongeur are used to remove all remaining cartilage from the subtalar joint. Flat cuts in the subtalar joint can remove excessive bone, particularly from the inferior aspect of the talus. The subchondral bone is perforated using a 2.5- to 3.0-mm drill bit and a curved osteotome.
A bone graft from the distal fibula and medial malleolus, with or without the addition of allograft adjuvants, is placed evenly across the ankle and subtalar joints (Figures 3A-3E). At this point, the ankle and subtalar joints can be manipulated in multiple planes to achieve neutral coronal, sagittal, and axial alignment. With both the ankle and hindfoot held in a neutral position, multiple Steinman pins and K-wires in different orientations are inserted through the plantar aspect of the heel to hold the ankle and subtalar joints in place temporarily. Wires are cut short to prevent interference with subsequent foot olive wire placement through the frame.
Continue to: X-rays should be carefully checked...
