OVERVIEW

Over the past decade, a resurgence of interest in total ankle replacement (TAR) has emerged, largely as a consequence of an improved understanding of ankle kinematics, better implant designs, and advances in surgical techniques producing better results and long-term outcomes. As a result, the implants in current use have experienced greater popularity. The longevity of these arthroplasties, regardless of design, is as yet unpredictable, with unknown long-term survivorship. Quite apart from the short-term failures, which mostly are related to wound healing, it is the longer-term potential for complications that is of greatest concern. In view of the potential for failure of a primary joint replacement related to poor bone quality (as a result of either osteopenia or avascular necrosis), as well as the intermediate- and longer-term complications such as osteolysis, subsidence, and loosening, careful consideration of the available salvage options is essential.

Failure of ankle replacements may be the result of patient, implant, or surgical factors, or a combination thereof. Poor selection of patients stemming from lack of attention to physiologic (comorbid conditions, obesity), psychological, and lifestyle factors (occupational and recreational) can jeopardize the outcome. Outcomes can be affected by surgical decisions or technique dictating implant choice, sizing, placement, and alignment; balancing of varus and valgus deformity; and adequately addressing coexisting hindfoot arthritis and deformities. Other uncontrollable factors such as soft tissue complications, wound breakdown, deep infections, and intraoperative technical failures, and fractures of bone or components also can cause failure.

Avoiding complications to begin with is always preferable than having to manage them after failed surgery. Optimizing outcomes begins with patient selection. The factors that I take into consideration are the patient’s activity level, lifestyle, and interest in exercise. The limb alignment, the quality of the bone, and the presence of adjacent joint arthritis are important. I may exclude patients who smoke and those in whom the surgery poses too high a risk, including those with peripheral vascular disease, diabetes, peripheral neuropathy, and skin conditions that preclude use of the appropriate surgical approach. Problems with wound healing may occur with increased frequency in patients who smoke and older patients with peripheral vascular disease. Bone quality is important as well, particularly in those patients with periarticular osteopenia, who have a higher risk for subsidence. Avascular necrosis of the talus does not preclude TAR, particularly with partial involvement of the joint. Even with severe avascular necrosis, an arthroplasty using a custom long-stem talus component may be considered. The larger or heavier patient should be very carefully selected, even if sedentary, and if osteopenia is present I do not perform arthroplasty.

MANAGEMENT OF FRACTURES

The medial malleolus is at risk for fracture regardless of the type of implant used, but more so with the Agility prosthesis, for which a vertical cut is made in the malleolus. For malleolus-sparing procedures, the risk for fracture is nevertheless still present, and in any patient with osteopenia, I protect the malleolus with prophylactic pinning. I insert two Kirschner wires (K-wires), and if there appears to be higher risk for malleolar fracture, I use cannulated screws over the guide pins. The medial malleolus is at particular risk for fracture in the patient who has sustained a previous fracture, and in whom the screws are still present and are in the path of the prosthesis (Figure 25-1). If the implant can be inserted with the screws left in, this is preferable, but if hardware removal is necessary, then multiple guide pins or K-wires should be inserted to protect the malleolus.

Figure 25-1 A and B, In ankle replacement surgery, nothing is more challenging than posterior screws blocking the path of the tibial component. I therefore prefer to stage this procedure, to ensure that the hardware is removed with no complications, and then proceed with the joint replacement at a subsequent date. (Because it is often fraught with unexpected problems, hardware removal can be a humbling experience.)

The largest-sized prosthesis available that will fit adequately should always be used, but care should be taken not to encroach on the medial malleolus. All tibial components are designed as a press fit—they should be reasonably tight-fitting, but not at the expense of risking fracture. It is important to be flexible regarding the size of the components and to change the size during the procedure as needed. For the Agility prosthesis, cutting additional bone from the medial malleolus should be avoided when possible; no more than 25% of the malleolus should be removed. A common error leading to fracture of the medial malleolus is making an oblique (not vertical) cut of the medial malleolus, such that when the tibial component is inserted, the posterior margin of the component abuts the obliquely cut medial malleolus.

If fractured, the medial malleolus must be fixed using small cannulated screws or a tension band during the same procedure. The replacement is at tremendous risk for subsequent disaster unless the malleolar fracture is treated accurately. It is essential to make sure that there is no deformity of the foot causing subsequent stress of the malleolus, which would be the source of a delayed malleolar fracture. This pathogenic mechanism is more common with a valgus foot deformity, with stress on the deltoid and medial malleolus. It may be necessary to sacrifice some range of motion for the need for stability and to immobilize the ankle postoperatively. Screw fixation should be used as a preventive measure in patients with severe osteopenia, and a fracture that occurs intraoperatively should always be repaired with screws (Figures 25-2 and 25-3).

Figure 25-2 A-C, A greater degree of osteopenia was found intraoperatively than had been expected. Accordingly, two cannulated screws were inserted before the tibial osteotomy cut was made.

Figure 25-3 A-C, A fracture occurred intraoperatively when the tibial bone was being removed. The osteotomy had been performed, and as the bone was being removed, the malleolus cracked. Even though the fracture was not displaced, cannulated screws were inserted to maintain stability.

In general, I am not as concerned for the fractured fibula, because these fractures are easy to fix. Once again, if a fracture occurs, it must be surgically stabilized and the anatomy restored. Fractures may occur inadvertently with the cut on the tibia, regardless of the type of prosthesis (Figure 25-4). Severe valgus instability with lateral shift and tilt of the talus may result. Although all implant procedures carry a risk of fracture, the risk is higher with use of the Agility prosthesis, which emphasizes the enhanced stability of the tibial component by syndesmotic fusion. A point to remember is that the fibula lies far posteriorly relative to the tibia and is at risk for fracture when the tibial cut is made. Another source of fracture with the Agility prosthesis is overcompression of the fibula during syndesmotic screw fixation. This too presents a potentially serious problem: overcompressing the fibula can cause valgus failure of the prosthesis. Because a plate is routinely used on the fibula to enhance syndesmosis fusion, the complication of fibula fracture is not as important, but the alignment of the fibula must be maintained.

Figure 25-4 A-C, Fracture of the medial malleolus occurred 7 months after Mobility ankle replacement. The alignment of the foot was good, and no significant edge loading of the medial malleolus was apparent. Because the alignment was good and no displacement was present, immobilization without fixation constituted appropriate treatment. D-F, Good range of motion of the ankle was evident on a lateral radiograph obtained 2 years later without deformity.

MANAGEMENT OF WOUND HEALING PROBLEMS

The soft tissues surrounding the ankle joint are not well vascularized and are relatively thin and tenuous. No deep subcutaneous tissue or muscle is present surrounding the ankle, and there is little to locally cover the components in the event of wound dehiscence. The blood supply to the extremity must be monitored with measurement of the ankle-brachial index in the elderly if pulses are questionable. Patients with rheumatoid arthritis, particularly those on immunosuppressant medications or prednisone, lose subcutaneous fat, and their thin fragile skin is more prone to wound complications.

Perhaps the most important preventive measure is to avoid any retraction and tension on the skin margins during surgery. The incision should be long enough to allow for optimal exposure without excessive retraction. I do not retract the skin edges until the periosteum is reflected, and I do not perform any simultaneous medial and lateral retraction at the same skin level. In fact, if visualization is inadequate with simple finger retraction, a slightly longer incision probably is necessary. Exactly what constitutes too much retraction of the skin to cause wound breakdown is not known, but blood flow must be maintained. The anterior tibial tendon should not be exposed at all, and if retinaculum over the anterior tibial tendon is not preserved with the incision, it must be repaired.

A minor dehiscence of the incision is not uncommon postoperatively. The very best treatment of this complication is use of simple topical antibiotic agents, dressing changes, and topical care of the skin (Figure 25-5). If a superficial dehiscence occurs, it is treated with daily changes of wet-to-dry saline dressings. I like to use a wound vacuum-assisted closure (VAC) device whenever there is drainage with breakdown of the incision. Deeper wound breakdowns are treated with silver sulfadiazine (Silvadene) dressings. If an eschar develops over an area of the incision, it is best left alone. The wound is not debrided and is kept as dry as possible (see Figure 25-5, C–F). The size of the eschar does not seem to be of any consequence, and over time and in the absence of infection, these dry eschars demonstrate quite a remarkable potential for healing. With more extensive wound dehiscence and exposure of the anterior tibial tendon, the use of a wound VAC device works well; in this setting, formal debridement of the wound and tendon is not necessary, because the VAC device may promote granulation and complete coverage of the tendon, without increased risk of infection. If deeper breakdown does occur, and the component is potentially exposed, coverage with a free flap usually is required to prevent infection and failure of the joint replacement. Removal of the prosthesis should not be necessary if coverage is adequate. I have no experience with acute infection of the joint; if this occurs, however, exchange of the polyethylene (“poly”) insert plus irrigation as is performed for other joints would be prudent.

Figure 25-5 Wound healing complications are common after ankle replacement procedures. A and B, Minor dehiscence is not a concern. C, Eschars should be left intact, kept dry, and left to granulate in from below. D-F, Even a very large eschar will eventually fill in well without infection, in the absence of peripheral vascular disease. In the case shown, the patient had rheumatoid arthritis, probably with mild vasculitis, and it took 7 months for the eschar to heal. The ankle replacement was performed 4 months after a triple arthrodesis.

More advanced infection should be treated with removal of the components, insertion of an antibiotic spacer, and administration of intravenous antibiotics. Although antibiotic beads can be made to fill the gap, a solid cement spacer acts to keep the joint space open, distracted at the correct soft tissue tension, and more stable. I permit patients to walk on the ankle as soon as the skin incision has healed after treatment of infection, without concern for any further bone loss or subsidence. After 6 weeks, an aspiration of the joint is performed, and if results of aspirate culture are negative, 4 weeks later the prosthesis is reimplanted. Before the surgery, I take a biopsy specimen of the synovium, and if the cell count is greater than 6 white blood cells per high-power field, the joint is debrided and another antibiotic cement spacer is inserted until the joint is proved to be infection-free. It is curious how well some patients tolerate the cement spacer. One of my patients who underwent an ankle replacement 5 years earlier developed a deep infection shortly after surgery performed through a lateral incision. The prosthesis was removed, and an antibiotic-impregnated cement spacer was inserted. During his subsequent follow-up care, the patient commented that this was the best that his ankle had felt in years, and he did not desire any further treatment. At the 5-year follow-up evaluation, no evidence of subsidence or erosion of bone was found, and the patient retained approximately 15 degrees of motion (Figure 25-6).

Figure 25-6 An ankle replacement performed in a 71-year-old man was complicated by a deep infection developing shortly after surgery. The prosthesis was removed, and an antibiotic-impregnated cement spacer was inserted. During subsequent follow-up care, the patient commented that this was the best that his ankle had felt in years, and he did not desire any further treatment. A and B, At 5 years, no subsidence or erosion of bone is evident, and the patient has retained approximately 15 degrees of motion.

CYST FORMATION

The early detection of loosening and subsidence is not easy, requiring a high index of suspicion, thorough history and examination, and various investigations to confirm the type of loosening. The typical history in patients with loosening of prosthetic components is one of pain on starting up with activities that is relieved shortly thereafter once “warm-up,” has been achieved. If the patient presents with pain and difficulty with ambulation, the decision to investigate the cause further, usually with computed tomography (CT) scan, may be more readily made. The situation is very different, however, if the patient presents with an asymptomatic cyst. These cysts can be massive and presumably arise in response to irritation from polyethylene wear debris, secondary to abnormal joint mechanics and typically worsening over time.

If the patient presents with an asymptomatic cyst on the plain radiograph, obtaining a CT scan is helpful, but the surgeon must be prepared to perform a revision if the size of the cyst is progressively enlarging (Figure 25-7). The CT findings are always far worse than expected, and as noted, these cysts can be quite massive.

Figure 25-7 A, The patient underwent ankle replacement 8 years earlier and was entirely asymptomatic. B and C, The appearance of the cysts on a computed tomography scan was far worse than that on the plain radiograph.

“Expansile” osteolysis resulting from polyethylene wear debris tends to progress, with consequent destabilization of the implant, leading to loosening and, ultimately, periprosthetic fracture. So, despite the total lack of symptoms in some patients, I try to encourage them to understand the cause, with its implications for the need for a timely revision to prevent catastrophic mechanical failure and to preserve and supplement the remaining bone support. A real therapeutic dilemma arises if the patient is asymptomatic, with good range of motion, and plain radiographs and CT scans show an apparently stable prosthesis but large osteolytic cysts. It is hard to convince a patient to undergo a revision when the joint is entirely asymptomatic. Serial investigations and close follow-up examination may be acceptable to help the patient decide when a revision or bone grafting is needed.

These large asymptomatic cysts are worrisome. I do not know what the natural history is of these cysts, but it is reasonable to assume that they are progressive and will ultimately perforate the tibial or talar cortex, making revision more complicated. No studies quantifying the rate and exact likelihood of bone defect progression have been performed. Many prosthesis designs are difficult to evaluate radiologically, particularly on the talar component side, because here it is not possible to see if there is any structural loss of bone support underneath. For example, in the Salto, STAR, and Hintegra systems, the talar component covers the body of the talus, which can “hide” what is going on underneath it, thereby masking bone necrosis. Earlier signs such as periprosthetic radiolucent lines also should be looked for on serial follow-up radiographs. CT scans are very helpful to evaluate for cystic defects or loosening.

Once a decision for surgical management of the cysts has been made, it generally is necessary to revise the prosthesis, or at the very least, the “poly” liner. Generally, there is some minor abnormality with alignment causing the abnormal poly insert wear. The cysts often are far deeper than is apparent on plain radiographs, and a large curette is used to remove the lining of the cyst without perforating the bone. I pack the cyst with a mixture of cancellous allograft chips and an iliac crest aspirate concentrate. The cancellous graft is packed in firmly, particularly when the bone loss is at the margin of the tibial component (Figure 25-8

Related posts:

The Modified Ludloff Metatarsal Osteotomy Hallux Varus Tibiotalocalcaneal and Pan-Talar Arthrodesis Arthrodesis of the Tarsometatarsal Joint Correction of Flatfoot Deformity in the Adult Arthrodesis of the Hallux Metatarsophalangeal and Interphalangeal Joints

Stay updated, free articles. Join our Telegram channel

Join