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.
JOINT COMPRESSION AND FINAL FRAME ADJUSTMENTS
Once all rings are secured to the bone with half-pins and wires, the previously placed Steinman pins, and K-wires through the heel are removed. Both ankle and subtalar joint alignments are rechecked, and then axial compression is placed through the foot ring with the knee extended and the struts unlocked. Static or telescopic struts are used to achieve 8 to 10 mm of bony compression. X-rays are taken before and after to analyze final joint compression and alignment. Struts should be sequentially tightened (1/2 turn of a static strut) 1 at a time as final tightening of 1 strut alone can bind and interfere with both the compression and tightening of the remaining struts.
Once final compression is achieved, the struts are locked, and the front foot arch is closed anteriorly and connected to the distal tibia ring for increased stability (Figures 6A-6D). Each pin and wire is covered in a sterile dressing followed by gauze to allow for soft tissue padding. The entire frame is then overwrapped in bias stockinette rolls or ace wraps.
Walking attachments can be added immediately to the frame that allows for early weight-bearing. Rocker shoe attachments with a 15° anterior and posterior slope and rubber soles can help offload the ankle and subtalar joints, decrease pressure on heel strike, and reduce ankle motion during ambulation (Hoffmann LRF, Stryker).
POSTOPERATIVE PROTOCOL
Depending on individual characteristics, patients can be immediately weight-bearing in the circular frame. Patients with Charcot neuroarthropathy are recommended to remain non-weight-bearing for the first 2 months to reduce the likelihood of pin, wire, and frame breakage along with nonunion. Pin and wire site care and maintenance are initiated the day after surgery and continue on a daily basis for the duration of frame placement. Sutures are removed 4 to 5 weeks after surgery to ensure adequate wound healing. Serial X-rays are taken monthly to analyze fusion sites.
If pins or wires become infected, patients are placed on oral antibiotics, and both pins and wires can be removed or exchanged in the operating room. Once fusion is achieved in 3 to 8 months (Figures 7A-7C), the frame is removed in the operating room, and fusion sites are examined under dynamic fluoroscopy. If fusion is confirmed, patients are made weight-bearing as tolerated in a short-leg cast or tall CAM boot for 6 to 8 weeks, and then transitioned to an ankle brace in an accommodative shoe.
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