Abstract
Whenever possible, it is preferable to perform a tibiotalocalcaneal (TTC) arthrodesis instead of a pantalar arthrodesis. Including the transverse tarsal joint in the arthrodesis, which results in far more rigidity to the foot, is rarely necessary. When performing a talectomy and a tibiocalcaneal (TC) arthrodesis, we leave the navicular bone free of the anterior aspect of the remnant of the talus. With some deformities, the entire talus must be removed, and the anterior tibia will then abut the navicular. In patients with neuropathy and a Charcot deformity including the navicular bone in this arthrodesis is tempting because it will increase the surface area for the arthrodesis. In this manner, after a cheilectomy of the anterior distal tibia and debridement of the navicular, a tibionavicular arthrodesis can be added to the TC arthrodesis. In general, however, we do not consider this additional fusion to be advisable, because the function of the foot, particularly in the setting of a neuropathy, is better without it, as the increased loss of motion imparted from this additional arthrodesis creates a more rigid deformity that increases the risk of ulceration in this patient population. Thus the only indications for a pantalar arthrodesis are to address severe pantalar arthritis and to correct a deformity of such magnitude that a TTC fusion alone will be inadequate.
Key Words
tibiotalocalcaneal, pantalar, arthrodesis
Overview
Whenever possible, it is preferable to perform a tibiotalocalcaneal (TTC) arthrodesis instead of a pantalar arthrodesis. Including the transverse tarsal joint in the arthrodesis, which results in far more rigidity to the foot, is rarely necessary. When performing a talectomy and a tibiocalcaneal (TC) arthrodesis, we leave the navicular bone free of the anterior aspect of the remnant of the talus. With some deformities, the entire talus must be removed, and the anterior tibia will then abut the navicular. In patients with neuropathy and a Charcot deformity, including the navicular bone in this arthrodesis is tempting because it will increase the surface area for the arthrodesis. In this manner, after a cheilectomy of the anterior distal tibia and debridement of the navicular, a tibionavicular arthrodesis can be added to the TC arthrodesis. In general, however, we do not consider this additional fusion to be advisable, because the function of the foot, particularly in the setting of a neuropathy, is better without it, as the increased loss of motion imparted from this additional arthrodesis creates a more rigid deformity that increases the risk of ulceration in this patient population. Thus the only indications for a pantalar arthrodesis are to address severe pantalar arthritis and to correct a deformity of such magnitude that a TTC fusion alone will be inadequate.
The surgical approach for exposure in a pantalar arthrodesis is almost identical to that for a combined ankle and triple arthrodesis. One surgical approach is to use the mini-arthrotomy approach with two anterior incisions and then extend these distally once the ankle is completely debrided. The medial incision is extended distally from the ankle to expose the talonavicular (TN) joint. Laterally, however, if the incision for the ankle arthrodesis is extended distally, then one incision is placed slightly anterior or dorsal to the calcaneocuboid (CC) joint. Alternatively, an approach that is used for an open anterior ankle arthrodesis can be performed between the anterior tibialis and the extensor hallucis longus with distal extension slightly medial to expose the TN joint. A standard sinus tarsi incision can be used to expose the subtalar joint and can be extended distally to visualize the CC joint if required. A fibulectomy should not be performed, if possible. In the case of severe varus, resection of the distal fibula at the level of the ankle joint can be performed to allow for deformity correction. The same rationale applies with a pantalar arthrodesis as with the ankle arthrodesis: preservation of the fibula is desirable because the blood supply to the ankle is maintained. Likewise, preservation of the medial malleolus is preferable, although at times, correction of ankle deformity cannot be accomplished without either an osteotomy or a resection of the medial malleolus. An important case in point is that of a TTC arthrodesis with intramedullary (IM) rod fixation, in which slight medial translation of the foot under the tibia is helpful. This translation can be accomplished only if the medial malleolus is removed.
For fixation of the pantalar arthrodesis, the approach is similar to that outlined for the screw technique used for a TTC arthrodesis. The only difference is that here the fixation of the TN joint can be extended proximally into the tibia with screws started at the inferior pole of the navicular bone, which cross both the TN and the tibiotalar joints into the back of the tibia.
Tibiocalcaneal and Tibiotalocalcaneal Arthrodesis
Fixation Alternatives
The fixation options for a TC arthrodesis are screws, a contoured plate, a blade plate, or an IM rod. To some extent, the choice of fixation may depend on personal preference, but at times a more stable fixation with either a blade plate or an IM rod is preferable in the setting of significant bone loss and deformity. In our experience, when any erosive changes or avascular necrosis of the ankle is present, screws may not be strong enough, particularly with neuropathic deformity. Historically, a blade plate has been demonstrated to be biomechanically superior to an IM rod in torsion and bending strengths, but this finding was reported with use of an inferior IM rod device; by comparison, the current rod designs include capability for internal and external compression as well as locking mechanisms for the distal screws to create a fixed-angle device similar to the blade plate.
Thus with the newer designs of the IM nail, rod fixation is preferable to use of a blade plate, provided that sufficient calcaneal bone is present. If the calcaneal bone is of poor quality, the posterior-to-anterior screw can be inserted across the CC joint into the cuboid bone. Postoperative weight-bearing status may also be a consideration. In patients in whom compliance with a non-weight bearing regimen is in question, we prefer to use an IM rod that can be dynamized if necessary. Although the locking screws may break, a nonunion is not as worrisome in the setting of neuropathic deformity, provided that the foot remains axially aligned under the tibia. The use of an IM rod also minimizes the need for a fibulectomy, minimizing the soft tissue injury. In cases without significant deformity, we have been able to arthroscopically prepare the ankle joint combined with a small sinus tarsi incision limiting the soft tissue dissection. Fixation with an IM rod or isolated screw fixation is possible in this scenario, whereas the use of a blade plate or precontoured locking plate would require a much larger soft tissue exposure.
We have used screws alone for a TTC fusion, but only when the bone quality is good, the alignment of the limb is not significantly abnormal, and focal arthritis is present without bone loss or avascular necrosis ( Figs. 32.1–32.4 ). We rarely use screws alone when the talus is missing and the overall alignment of the limb is not satisfactory. Therefore at present, for a TTC arthrodesis, we use screws for correction of minimal deformity in ankles with good bone quality and an IM rod in a majority of the remaining cases. A blade plate or anatomically designed TTC plates remain useful when tibia deformity is present, if an IM rod cannot be used, or if a simultaneous tibial osteotomy cannot be performed for realignment.
Surgical Approaches
A lateral transfibular approach to the ankle and hindfoot can be used for correction of severe deformity. Although this distal fibulectomy will devascularize the lateral ankle, an alternative is often unavailable for correction of severe deformity, particularly when the ankle is angulated and in varus and the fibula is prominent. The incision is made vertically, directly over the fibula, extending down distally over the sinus tarsi toward the inferior aspect of the calcaneus. The sural nerve must be identified and then retracted inferiorly with the peroneal tendons. A fibulectomy is performed with an acetabular reamer, which is used to completely denude and decorticate the fibula. The reamings that are obtained are preserved for later use as bone graft material ( Fig. 32.5 ). Alternatively, to decrease the risk of devascularization, the fibula may be osteotomized at the level of the ankle joint, may be removed leaving the syndesmotic articulation intact. This will prevent injury to the peroneal artery and allow both access to the ankle and subtalar joint combined with the ability to reduce the varus deformity. If this technique is used, an IM nail is required as opposed to a plate, given that the remaining fibula will prevent appropriate plate placement.
If a blade plate or anatomic locking TTC plate is to be used for fixation, the distal 8 cm of the fibula must be removed, and following use of the reamer, the fibula is cut with a saw. We prefer to use a chisel and not a saw to denude the ankle and subtalar joints. If severe deformity is present, however, then the distal tibia may have to be cut at the plafond with a saw. Often the foot cannot be centered under the ankle because the medial malleolus blocks the shift of the talus. In such instances, the malleolus is removed with an oblique osteotomy made through a separate medial incision. The dissection in the sinus tarsi and subtalar joint is performed in the same manner as that described for a subtalar arthrodesis.
Another indication for TTC arthrodesis is that following a failed ankle replacement. Despite the increased success of the recent generation of implants, implant failure occurs, and although revision of the replacement can be performed, arthrodesis is at times required. In some cases, an isolated bone block ankle fusion is possible; however, lack of sufficient talar bone stock may result in the need to perform a TTC fusion. The surgical approach for these cases is determined by the prior incision required for the arthroplasty. To obtain access to the subtalar joint, a small sinus tarsi approach can be used that allows for a sufficient skin bridge, as the anterior approach for the replacement is typically angulated medially toward the TN joint.
When a talectomy plus a TC arthrodesis is performed for avascular necrosis (AVN), the necrotic remnants of the talus are completely excised. A sizable defect remains; either it can be filled with bone graft or the talus can be apposed directly onto the calcaneus ( Fig. 32.6 ). Usually, despite the contouring of the posterior aspect of the calcaneus and the undersurface of the distal tibia, joint apposition cannot be easily obtained. It is difficult to appose the calcaneus flush up against the tibia, because the hindfoot tilts up into dorsiflexion, leaving the hindfoot in a calcaneus position. A defect of variable size, depending on bone erosion, is always present between the undersurface of the tibia and the dorsal surface of the posterior facet; the shape of the defect may range from a trapezoid to a large triangle. At times, if the apposition between the tibia and the calcaneus is very good and the defect is not too large, it can be filled with cancellous graft only. Some bone graft is needed in the more anterior aspect of the arthrodesis to fill the defect properly. Here either cancellous graft or a tricortical structural allograft can be used; the choice will depend on the availability of large structural graft and the size of the defect. It is clearly easier to secure the posterior tibia to the dorsal calcaneus and then fill the defect with cancellous graft. Over the past several years, with the increased use of orthobiologic adjuvants, the latter has been our preferred technique. We use a structural graft when the height of the limb must be restored. In some circumstances, this structural graft has to be used between the tibia and the calcaneus. Of note, in performing a talectomy and TC arthrodesis, as the heel is pushed up against the tibia, the skin on either side of the ankle gets compressed, and closure can no longer be achieved without tension on the skin (the so-called “accordion effect”: as the structure is elongated, it narrows, and as it is compressed, it widens). In the setting of a TC fusion with structural allograft, an anterior approach may be considered especially in the setting of a prior total ankle arthroplasty, as this may minimize the risk of wound complications as the old incision may be used. Following implant removal, exposure is excellent, and joint preparation of the calcaneus with an acetabular reamer will facilitate joint positioning ( Fig. 32.7 ).
It is not easy to insert the structural graft and obtain compression as well as stability between the tibia and calcaneus. One method that works well is to align the calcaneus under the tibia and then secure this position with guide pins. With the foot now quite stable, it is forced into plantar flexion while the pins are in place. With the foot plantarflexed, the TC gap opens and the graft is inserted and tamped into place securely. The foot is now maximally dorsiflexed, and the bone graft is compressed between the calcaneus and the tibia, followed by definitive fixation ( ).
If there is significant bone loss or partial AVN of the talus, it is far preferable to approach the ankle without any potential for further devascularization. Certainly, a lateral transfibular approach with fibulectomy does not make any sense in the presence of AVN since this deprives the arthrodesis site of any revascularization through the peroneal artery and its branches, which are completely disrupted with a fibulectomy. For these and other patients, a posterior approach to the ankle may be considered. It has numerous advantages including a direct approach to both the ankle and subtalar joints, minimal if any devascularization, and the ability to easily control rotation of the limb, which is almost impossible to do from the lateral decubitus position. An incision is made posteriorly straight through the Achilles tendon, which is split and then cut proximally and distally. The ends are sutured to the skin to move them out the way. It has never been clear what, if any, function the gastrocnemius-soleus has following a TTC arthrodesis; nonetheless, we prefer to preserve the tendon and suture it at the completion of the procedure. Once the soft tissue has been moved away from the posterior tibia, the ankle and subtalar joints are visible. If not, insert a curved osteotome into the joint to verify its position under fluoroscopy and commence with debridement and joint distraction. One can either use a laminar spreader or a pin distractor (which is our choice) to gradually open the joint. Both joints are opened and debrided thoroughly. It is never a concern how to get to the anterior aspect of the subtalar joint, which is always possible, and even the ankle can be debrided up to the anterior joint with appropriate curettes ( Fig. 32.8 ). During the exposure and continued debridement, it is common to see the flexor hallucis longus (FHL) tendon; if so, then as long as one is working anterior to the tendon, there is no risk of injury to the neuromuscular bundle.
