OVERVIEW

This chapter outlines the indications for ankle replacement in the ideal patient, as well as in those patients for whom this procedure poses a higher risk for failure. Descriptions of the different prostheses I use for ankle replacement, as well as techniques and tips for each type of implant device, also are presented. The step-by-step process is not reviewed for each procedure, although critical techniques for specific implants are highlighted.

Who is the ideal candidate for an ankle replacement? What should the surgeon tell a patient who presents with ankle arthritis, and how should decision making proceed in this setting? Selection of the treatment approach should not be the surgeon’s decision alone. For an ideal patient with good alignment, good bone support, and reasonable range of motion, with no contraindication to joint replacement, what is the best surgical advice? What are the advantages of ankle replacement over arthrodesis? Is the functional improvement with ankle replacement so much greater than arthrodesis that it warrants performing the procedure despite its much higher complication rate? Many patients recognize the potential problems with ankle arthrodesis, the inherent stiffness, the limitation to certain activities, and in particular the likelihood of adjacent joint arthritis developing in the future. Within this group of patients, however, some prefer not to deal with potential for failure of an ankle replacement and want more predictability in the outcome and therefore select the arthrodesis. I outline all of the potential advantages and disadvantages, as well as the possibility of complications for each procedure; selection of the most appropriate procedure then becomes a joint decision that the patient and I make together.

An important consideration in surgical planning is the preoperative range of motion of the ankle. One of the most critical factors affecting the postoperative range of motion is a preexisting contracture, which is often the case with posttraumatic arthritis. The soft tissue envelope around the posttraumatic and arthritic ankle joint usually is quite scarred, at times significantly so. Contractures developing over long-term periods of immobilization further adversely affect the ankle joint mobility. In such cases, it is more difficult to obtain a satisfactory range of motion even intraoperatively, despite aggressive soft tissue release. A patient with severe ankylosis may never achieve an acceptable range of motion regardless of how the procedure is performed. For such patients, arthrodesis may not be perceived as disabling (in comparison with those in whom the clinical presentation includes a reasonable range of motion but some degree of preoperative pain) (Figure 24-1). It is important to identify the true range of motion of the ankle joint, which can be clinically deceptive because “motion” may actually represent mobility of the transverse tarsal joints (Figure 24-2). I routinely obtain dynamic lateral plantar flexion and dorsiflexion radiographic views of the ankle during the preoperative evaluation to identify the exact location of sagittal plane motion.

Figure 24-1 The range of motion of the ankle is important in surgical decision making and may have no correlation with the radiographic appearance. A-C, In this example, a patient with hemachromatosis had severe ankle arthritis but retained excellent range of motion. D-F, By contrast, a patient with posttraumatic arthritis may have no ankle motion at all despite only moderate arthritis as indicated by radiographically evident changes, as in this case. This patient may be a better candidate for an ankle arthrodesis than another patient with excellent motion but with far more extensive radiographic changes, for whom a replacement is preferable.

Figure 24-2 A and B, The patient developed ankle arthritis after treatment of a pilon fracture requiring plate fixation and a free flap. He was not a good candidate for replacement. Minimal motion was present in the ankle, and the flap could not be safely elevated. The hardware would need to be removed, which would add to the soft tissue dissection. Even if this patient had good anterior skin, it would still be necessary to remove the hardware as a staged procedure and perform the replacement months later, once the skin bridge was less likely to fail.

The alignment of the foot and ankle is an important determinant of suitability for replacement surgery. There are limits to correction of a varus or valgus deformity, which I generally set at approximately 20 degrees for varus and 10 degrees for valgus. As discussed later in the section on managing associated deformity, if the deltoid ligament is torn, the likelihood of obtaining a well-aligned ankle is significantly decreased (Figures 24-3 and 24-4). Tibia varus or valgus deformity should be addressed before ankle replacement, particularly if the knee is affected, in which case the knee must be first corrected (Figure 24-5).

Figure 24-3 A and B, This varus deformity was fixed, and the joint was not passively reducible. At 25 degrees of varus angulation that was irreducable, this is excessive, and a joint replacement was not contemplated.

Figure 24-4 A and B, This varus deformity is not excessive and could be be treated with ankle replacement. Of note, the marked compensatory deformity of the foot must be corrected simultaneously, to avoid recurrent ankle deformity. C and D, Note the medial translation of the foot under the tibia; despite the varus ankle deformity, the hindfoot is in valgus and the midfoot is unstable. If the ankle varus deformity is corrected, greater valgus deformity of the foot will result.

Figure 24-5 Joint replacement should be staged if there is tibia vara. The tibial osteotomy can, however, be performed simultaneously with the ankle replacement.

Bone quality is an important consideration, and if severe osteopenia is present, the likelihood of subsidence of the prosthesis is increased. The risk increases if avascular necrosis is present. The talar component is more likely to subside than the tibial component, particularly if osteopenia or avascular necrosis is present. To circumvent this problem of poor-quality bone, selection of a prosthesis with a long stem is a good option. This is combined with a subtalar arthrodesis, providing a very stable platform for the prosthesis (Figure 24-6).

Figure 24-6 A and B, Avascular necrosis and a valgus deformity of the talus treated with joint replacement with a long-stem talar component. The stress fracture of the fibula was the result of the valgus deformity. The replacement was performed in combination with a subtalar arthrodesis, and a long-stem talar component was used to overcome the poor bone quality and distribute the load into the calcaneus. C-E, Excellent range of motion of the ankle and a stable implant at 3 years after surgery.

Preoperative instability of the ankle is very important to ascertain, and treatment should be planned accordingly. Certain deformities seem trivial but should be approached with caution. An unstable ankle typically is thought to be associated with a lack of lateral ligamentous support. Such instability is problematic only if not identified intraoperatively, because a ligament reconstruction is always possible to restore stability. If the deltoid is torn, however, restoration of medial stability will be unpredictable. Another pattern of instability that is difficult to treat is anterior subluxation of the talus under the tibia (Figure 24-7). This displacement may resolve with correct positioning of the prosthesis and correct tensioning with a larger polyethylene (“poly”) insert, but the outcome is not predictable, and anterior subluxation should be approached surgically with caution.

Figure 24-7 A, Anterior subluxation of the ankle was noted preoperatively in a 70-year-old patient with ankle arthritis. B and C, At the time of surgery, the joint was well prepared for the Mobility prosthesis (DePuy Orthopaedics, Inc., Warsaw, Indiana), and the cuts made for the talar component were correctly centered on the talus, yet subluxation persisted. This was addressed by appropriate tensioning with the poly insert, and correct axial alignment returned 6 months after joint replacement.

Combined surgeries are commonly performed for associated deformity and arthritis. I recommend simultaneous hindfoot arthrodesis. The talonavicular arthrodesis is straightforward, because the incision is simply extended slightly distally. A lateral incision can be used for an isolated subtalar arthrodesis or a subtalar and calcaneocuboid arthrodesis (Figure 24-8). The fixation of these joints can be difficult, but correctly positioned screws or plates are used without interfering with the prosthesis. This consideration is of particular importance in patients with rheumatoid arthritis. Repeated bouts of immobilization lead to increased osteopenia with the potential for implant subsidence or fracture. Simultaneous joint replacement–arthrodesis has its advantages (Figure 24-9). If hardware is present in the tibia or talus, it obviously has to be removed if it interferes with correct positioning of either the tibial or the talar component. Of note, however, removal of hardware may create a stress riser, particularly in the medial malleolus (see Figure 24-9). Screws that strip on attempted removal constitute more of a problem: additional bone has to be removed to core out the screw with a screw removal device. Screws in the medial malleolus may interfere with insertion of the tibial component, and they should not be removed intraoperatively, regardless of the type of prosthesis, unless the malleolus is reinforced with temporary Kirschner wires (K-wires).

Figure 24-8 A subtalar arthrodesis was performed simultaneously with the joint replacement through a separate lateral incision. It is important to maintain as large a skin bridge as possible.

Figure 24-9 A and B, Ankle replacement for management of intractable posttraumatic arthritis. Note the medial malleolar screws. The screws were left in place, and the replacement was performed with a simultaneous subtalar arthrodesis.

TECHNIQUES, TIPS, AND PITFALLS

Replacement With All Implants

• After the skin incision the extensor retinaculum is carefully incised to create two flaps, which are not retracted during dissection until the tibial periosteum is reflected. The central aspect of the incision directly over the ankle is at the most risk for subsequent wound dehiscence, and very gentle retraction is necessary. Use finger retraction, and do not pull on the skin with an instrument. Simultaneous retraction of both sides of the incision should be avoided.

• For all implant systems, it is necessary to be able to change the size of the prosthesis at the final stage of the surgery. This is particularly the case if the range of motion is compromised, and under these circumstances, I down-size the prosthesis in the hope of improving the range of motion. Select the smaller prosthesis only if it adequately covers the cortical rims of talus and distal tibia and provides sufficient clearance. If the prosthesis has been correctly sized and matches the tibia and the talus, then it is preferable to recut the bone, which can be removed from either the talus or the tibia, depending on the available bone. If the plan is to remove more bone from the talus, then the amount to be removed should be projected by fluoroscopic imaging, to ensure that the posterior subtalar joint is not compromised. Any further cuts on the talus must therefore be made with the ankle fully dorsiflexed.

• Do not overstuff the joint, which will lead to stiffness, pain, and ultimate joint failure. If considering a lengthening of the Achilles tendon, review whether this is in fact necessary; it may be far simpler and ultimately more reliable to shave 2 mm off the tibial cut and decrease the tension on the joint.

• The retinaculum over the anterior tibial tendon must be carefully repaired if the tendon is exposed. In the event of a wound dehiscence, provided the tendon is not exposed, the management of the wound is not difficult. The anterior incision must protect the sheath of the anterior tibial tendon and should be made slightly lateral to the tendon. If the retinaculum tears, inserting a suture in it early is preferable to repairing the retinaculum after surgery to maintain the tendon in the sheath. The retinaculum must be closed to prevent bowstringing of the tendon and to minimize the potential for disaster if a wound dehiscence occurs postoperatively (see Figure 24-9, E).

• A synovectomy and debridement of these osteophytes will facilitate improved exposure, including a sense of the position and plane of the ankle joint. Performing an extensive ostectomy or cheilectomy of the anterior distal tibia to improve visualization of the joints is always helpful, regardless of the implant used. A problem may arise with exposure of the distal fibula at the talofibular articulation. This is not easy to visualize and is best done slowly, with movement of the ankle until the joint is easily visible.

• When the posterior tibial cut is made in cases of post-traumatic arthritis, removal of the posterior lip of the tibia is difficult. The tibia can be prominent posteroinferiorly, and the flexor hallucis and peroneal tendons may be scarred down to the underlying bone. Do not rip out the bone with a rongeur, but slowly remove the hypertrophic osteophytes with a pituitary rongeur. When making the tibial bone cut, pay attention to the posterior soft tissues, in particular the posterior tibial tendon and the flexor hallucis longus tendon, with the cut on the posterior aspect of the tibia. The posterior tibial tendon frequently is visualized with the medial malleolar cut (when the medial malleolus is cut as with an Agililty replacement), and it should therefore not be surprising that posterior tibial tendon symptoms may develop postoperatively. When the posterior tibial cut is made in cases of posttraumatic arthritis, it is difficult to remove the posterior lip of the tibia, and the flexor hallucis and peroneal tendons may be scarred down to the underlying bone. Do not rip out the bone with a rongeur, but slowly remove the hypertrophic osteophytes.

• A fracture of either malleolus must be recognized and fixed intraoperatively. Fracture of the medial malleolus creates more of a problem and usually is caused by a combination of osteopenia, previous stress on the medial malleolus (such as with a varus deformity), difficulty with sizing or positioning of the tibial component, or inadvertent manipulation of the ankle. If a fracture does occur intraoperatively, it should always be secured with internal fixation, because the malleoli are required for the stability of the prosthesis. Fracture of the medial malleolus creates more of a problem and usually is caused by carelessness with sizing or positioning of the tibial component or inadvertent manipulation of the ankle. Perhaps the most common error causing fracture of the medial malleolus is making an oblique (not vertical) cut of the medial malleolus, when the swing of the blade cuts deeper into the malleolus posteriorly.

• Once the trial components are inserted, it should just be possible to separate the components by a few millimeters from each other with maximal pulling on the ankle. This criterion ensures the correct tension.

• Initial splinting of the ankle joint in maximum dorsiflexion is essential to avoid creating an equinus contracture, because the dorsiflexion is difficult to regain later on. I do not like using the traditional splints—these are applied presumably with the foot in dorsiflexion; subsequently, however, because of the bulk of the dressing, the foot may be found to have drifted into equinus. A circumferential cast may be used but will need to be split in the recovery room.

• Early initiation of range-of-motion exercises is recommended. A fracture boot locked in extension should be used to immobilize the joint during the periods when exercise is not performed. Control of postoperative swelling minimizes patient discomfort and increases ability to perform the necessary exercises. Early weight bearing is permitted with the Salto prosthesis, and once the incisions are fully healed, the patient is permitted to begin swimming and walking in a pool. Progressive resistance exercises are gradually added to the postoperative rehabilitation regimen.

• Patient weight should be taken into consideration by the expected size of implant to be used and the body mass index. A large muscular man with a large joint who requires a large implant would be expected to have fewer complications with subsidence and wear than those typical for an obese patient of the same weight with a small ankle requiring a smaller implant. In general, the exact-size prosthesis should be inserted; in some instances, however, it may be best to “err” in one direction or another with regard to size. For example, in patients with severe ankle ankylosis secondary to trauma, an acceptable range of motion may not be attainable; this limitation can be minimized to some extent by downsizing the prosthesis.

Agility Ankle Replacement

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