Indications for the supramalleolar osteotomy are numerous and include correction of deformity, joint preservation, and as a staged procedure that leads up to other operations, including total ankle replacement as well as ankle and tibiotalocalcaneal arthrodesis. Osteotomy is performed for correction of a malunion of a distal tibial fracture, with or without ankle joint arthritis, to redistribute or beneficially alter the contact pressures on the degenerated cartilage with mechanical realignment. Osteotomy can be used for preservation of limb alignment as a prelude to a total ankle replacement. One of the prerequisites for a successful total ankle replacement is a balanced mechanical axis of the foot with respect to the lower leg, and a supramalleolar osteotomy works well as a staged procedure for the appropriate patient. The goal of osteotomy in the treatment of ankle arthritis is to shift the loads and redistribute stresses to a part of the ankle joint that is not involved in the degenerative process. The redirection of forces around the tibiotalar joint can be effected from above the ankle with osteotomy of the tibia and below the ankle with osteotomy of the calcaneus, respectively.
Key WordsOsteotomy, varus, valgus, supramalleolar, malunion
Indications for the supramalleolar osteotomy are numerous and include correction of deformity, joint preservation, and as a staged procedure that leads up to other operations, including total ankle replacement as well as ankle and tibiotalocalcaneal (TTC) arthrodesis. Osteotomy is performed for correction of a malunion of a distal tibial fracture, with or without ankle joint arthritis, to redistribute or beneficially alter the contact pressures on the degenerated cartilage with mechanical realignment. Osteotomy can be used for preservation of limb alignment as a prelude to a total ankle replacement. One of the prerequisites for a successful total ankle replacement is a balanced mechanical axis of the foot with respect to the lower leg, and a supramalleolar osteotomy works well as a staged procedure for the appropriate patient ( Fig. 20.1 ).
The goal of osteotomy in the treatment of ankle arthritis is to shift the loads and redistribute stresses to a part of the ankle joint that is not involved in the degenerative process. The redirection of forces around the tibiotalar joint can be effected from above the ankle with osteotomy of the tibia and below the ankle with osteotomy of the calcaneus, respectively. If either subtalar or supramalleolar deformity is present, the increased stresses on the tibiotalar joint may increase the likelihood of failure. The same concepts of realignment of the tibia apply to malunion after ankle arthrodesis. With the ankle joint fused in equinus, a leg length discrepancy is present because the involved leg is relatively lengthened. This disparity leads to a genu recurvatum thrust on the knee joint, an uneven gait pattern, and increased stress concentration across the midfoot. With the ankle fused in dorsiflexion, repetitive calcaneal impact and stress concentration on the heel pad during the heel strike phase lead to chronic heel pain and gait impairment.
Varus malunion of the ankle fusion causes the patient to walk on the lateral aspect of the foot. This inverted position of the subtalar joint increases the rigidity of the transverse tarsal joints, with substantial increase in stress concentration and subsequent degenerative changes and pain. In addition, stress is increased under the fifth metatarsal head or base, and development of painful calluses or stress fractures is not uncommon. Valgus malunion of an ankle arthrodesis generates increased stresses along the medial aspect of knee and hindfoot joints. In such a valgus position, the foot becomes more flexible, resulting in flatfoot posture. For all of these deformities, a revision of the ankle arthrodesis malunion is required but not at the level of the ankle itself. On the basis of the mechanical axis, a supramalleolar osteotomy is recommended.
Perhaps the biggest error in preoperative management and assessment of the ankle is that we are not treating the ankle, but the entire leg. How often do we approach a patient who has a varus distal tibia and obvious varus of the ankle and hindfoot and never lift up their pants above the knee to examine the knee alignment? The same can be said for radiographic evaluation, where long leg x-rays (XRs) are necessary and not merely standing XRs of the ankle. Not only are XRs of the knee to the ankle useful, but long leg XRs including the center of the hip to the center of the ankle have been demonstrated to be invaluable in planning osteotomy correction.
The opening wedge osteotomy has the advantage of avoiding leg shortening, but delayed union or nonunion may result because of the need to use a structural bone graft. Although the leg length change may not seem significant, if only 1 cm of shortening is performed with the wedge resection osteotomy, such change does become significant if an opening wedge osteotomy is performed with a 1-cm graft, when the height differential is almost 2 cm once the graft has healed. With any skin-related problems (previous incisions with scar formation or previous infection) or the potential for vascular compromise, a closing wedge procedure must be performed. The closing wedge osteotomy has a major disadvantage of limb shortening but is generally easier than the opening wedge procedure, particularly if both the fibula and the tibia are included. This concept of limb shortening is best exemplified in this patient with a severe posttraumatic varus deformity ( Fig. 20.2 ). We perform supramalleolar osteotomy whenever possible to preserve hindfoot alignment in cases of deformities secondary to neuroarthropathy or avascular necrosis of the distal tibia. Correction of neuropathic deformity with distal tibial osteotomy is an excellent alternative to a more extensive hindfoot and ankle arthrodesis, particularly in the setting of neuroarthropathy, and given the risks of a large structural bone graft collapse, a closing wedge osteotomy is performed for these patients. Whenever possible, arthrodesis should be avoided in patients with Charcot deformity, to prevent added stresses on the remaining hindfoot joints. The patient had neuropathy, and a dysvascular limb and had already undergone a peripheral bypass procedure. He was developing neuropathic ulceration over the lateral foot, and required a supramalleolar osteotomy for correction. Although preservation of limb length would be ideal, it would have been impossible here to predict the outcome in a dysvascular limb, and a closing wedge osteotomy was performed even though this was a very large wedge resection.
Use of wedge modifications allows correction of biplanar deformities. For example, a recurvatum-varus deformity can be corrected either with a posterolaterally based closing wedge osteotomy or with an anteromedially based opening wedge osteotomy. The size of the wedge is determined by drawing the desired correction angle on the preoperative radiographs, measuring the wedge size on a template, and taking magnification into account.
Measuring the center of rotation of angulation (CORA) of the deformity is important. The CORA is located at the intersection of two lines representing the mechanical axes of the proximal and distal segments of the deformity. A closing or opening wedge osteotomy at the level of the CORA leads to complete realignment of the foot and ankle. If the osteotomy is made proximal or distal to the CORA, the center of the ankle translates relative to the mechanical axis of the tibia and creates an unnecessary shift of loads and a clinically obvious zigzag deformity ( Fig. 20.3 ).
The osteotomy line should be translated and angulated so that a secondary translational deformity is not created when the osteotomy is intentionally made at a different level from that of the CORA ( Fig. 20.4 ), as with correction of an equinus malunion of an ankle arthrodesis. In this deformity, the position of the forefoot is fixed relative to the axis of the tibia. The simplest method of correction is to remove an anteriorly based wedge from the distal tibia and then close the osteotomy while maintaining the posterior cortex intact in a greenstick-type maneuver. The problem with this type of correction is that the foot is translated anteriorly relative to the tibia, and then the mechanical limb axis is no longer aligned or efficient for ambulation.
An important consideration is the extent of compensation that can be achieved by the ankle and subtalar joints after correction. Deformities in the coronal plane are well compensated by subtalar joint motion, and deformities in the sagittal plane are well compensated by ankle joint motion. For example, a varus deformity of the tibia is compensated by eversion of the subtalar joint. The ability of the hindfoot to compensate for a distal tibial deformity depends on whether it is in varus or in valgus. Because the hindfoot is able to invert far more than to evert, it can compensate for a valgus deformity far better, and the foot may still be plantigrade despite tibial deformity. This may not, however, be the case with a varus deformity, because the capacity of the hindfoot to evert is more limited.
Correction of Varus Deformity
For the correction of a varus deformity, we use either a medial opening wedge osteotomy or a lateral closing wedge osteotomy ( ). For the medial opening wedge osteotomy, we use an anteromedial and a small lateral incision (for the fibular osteotomy). Which cut is made first is a matter of preference, but leaving the fibula intact provides some stability while the tibial cut is completed. When the deformity is minimal, a greenstick cut of the tibia is made in the hope that a fibular osteotomy may not need to be performed. This greenstick cut markedly increases the stability of the osteotomy, and the tibia can be opened with a laminar spreader to the desired amount. The advantage of this sequence is that the tibia does not move around after the cut is made, as movement may compromise stability. Another alternative is to apply a three-hole plate to the lateral aspect of the distal tibia at the level where the osteotomy exits. With this technique, the osteotomy cut does not open, and the correct tension on the osteotomy can be applied until the ankle is plantigrade. The plate is applied just before the osteotomy cut exits the lateral tibial cortex. The opening wedge osteotomy is performed 4 cm proximal to the medial malleolar tip in metaphyseal bone, preferably at the level of the CORA ( Fig. 20.5 ). Where there is a clear CORA, it is generally preferable to perform the osteotomy at that location. In Fig. 20.6 , note that an opening wedge osteotomy was performed, which was consistent with the patient’s goals of returning to an active lifestyle with minimum leg length discrepancy.
Once the skin incision is made, minimal periosteal stripping that is sufficient only to complete the osteotomy is performed. The cut is planned in the metaphysis. We apply the selected plate on the surface of the tibia before the osteotomy is made, ensuring that sufficient space is maintained to obtain fixation with three screws distally, mark the osteotomy, and complete it. We keep periosteal stripping to a minimum when the bone cut is made perpendicular to the tibia with a broad oscillating saw, and preserve the opposite cortex and periosteal sleeve to act as a fulcrum for the opening wedge and to enhance stability. If nothing more than uniplanar angulation is required, then a small plate over the lateral tibia is useful to prevent overcorrection. If translation and rotation also are necessary, then the opposite cortex must be cut to allow the distal segment to move. The fibular osteotomy is performed with the lateral incision at the same level as that for the tibial osteotomy, although this location is not critical. A wedge osteotomy of the fibula can be performed if marked angular deformity is present and when a closing lateral wedge osteotomy of the tibia is performed. We prefer to use a structural allograft from a femoral head to fill the defect. Once the osteotomy has been performed, a laminar spreader is inserted to gradually distract the osteotomy to the desired level. This is checked fluoroscopically. The structural bone graft provides immediate mechanical support, with little likelihood of collapse even after resorption, which occurs during revascularization. To improve the rate and likelihood of bony integration, the use of osteoinductive graft is encouraged in addition to the structural allograft, whether demineralized bone matrix or concentrated bone marrow aspirate. Some structural integrity remains during the process of bone graft incorporation, to allow the graft to withstand loads. After the deformity has been corrected, the osteotomy is provisionally secured with Kirschner wires, and the plate is applied to the tibia at this time. The alignment is assessed with fluoroscopy.
In certain circumstances, the preservation of limb length is not necessary or desirable, so a closing wedge lateral osteotomy of the fibula and tibia is performed ( Figs. 20.7 and 20.8 ). Fig. 20.7 presents an example of chronic lateral ankle instability associated with a varus distal tibial deformity. We previously used a lateral closing wedge osteotomy for correction of this type of deformity, but over the years, we recognized that a defect of the medial distal tibia persists, so that recurrence of ankle varus is likely (see Fig. 20.7D ). Although symptoms are decreased, stability may not be regained, and it is unlikely that these intraarticular deformities can be satisfactorily treated with this approach. When performing a lateral closing wedge osteotomy of the tibia and fibula, we add a separate incision in a medial location to permit application of a small plate to the tibia, which prevents overcorrection. The osteotomy can be tensioned against the fixed fulcrum medially with this technique (see Fig. 20.8 ). In some cases, the varus deformity is the result of trauma and may be intraarticular with compression of the medial plafond. This varus deformity is particularly amenable to correction with osteotomy, but because of the proximity of the deformity to the plafond, it is preferable to perform a closing lateral wedge rather than a medial opening wedge osteotomy ( Fig. 20.9 ).