Nonunion of Malleoli and Symptomatic Implants
Malleolar nonunions are a frequent cause of pain in patients with total ankle replacements (Fig. 20–3A, B). Although intraoperative fractures should be fixed when they occur, often nonunions will develop as the patient begins weight- bearing. These must be treated relative to both clinical FIGURE 20–1.Clinical view of a failed total ankle anthroplasty with
valgus collapse.
FIGURE 20–2.Anteroposterior radiograph showing valgus collapse of tibial implant with syndesmotic nonunion and a loose talar component.
179 C H A P T E R20 Recognition and Salvage of the Failed Ankle Replacement Arthroplasty
symptoms and mechanical considerations. If the prosthesis is stable and the patient can tolerate the associated pain, noth- ing need be done. If the nonunion will result in component failure, then an attempt at a correction of the nonunion must be performed. On the other hand, if the prosthesis is secure, the syndesmosis and malleoli are healed and intact, but screws and/or plates are prominent, then these implants should be removed, typically in an outpatient setting.
Impingement
Most of the problems associated with impingement are a result of earlier versions of the talar prosthesis. This compo- nent did not cover the entire surface of the talus and as a result is somewhat unsupported. That being said, the talar component can become loose for a variety of reasons, includ- ing improper insertion and/or talar preparation, improper size selection, or failure of bony in-growth. Once the compo- nent becomes loose, it begins to move in its slot causing an inflammatory reaction and subsequent erosion of the talar surface. The combination of bone debris and inflammation- induced fibrous tissue results in a further deterioration of the joint. At some point, the prosthesis settles and the cut surfaces of the talus (the surfaces not covered by the prosthe- sis) now begin to make contact with the malleolar sides of the tibial component. This is defined asimpingement(Fig. 20–4).
When impingement and/or loosing is suspected and conservative (nonoperative) treatment methods fail, diagnos- tic and/or operative arthroscopy is advisable as the next method of treatment. This procedure may prevent or delay the need for further surgery. The arthroscopy itself will be a long procedure, as the surgeon must remove all excess fibrous tissue, which can be extremely stout and difficult to debride. Furthermore, it is only once excess fibrous tissue
and synovium are removed that bone overgrowth and pros- thetic loosening can be evaluated (Fig. 20–5).
If bone has overgrown the sides of the talar component, this bone should be burred or cut back. At this point the talar component should be tested for loosening. If loose, a gentle prying motion with a probe will result in gross motion of the component (Figs. 20–6 and 20–7). If no gross motion is
A B
FIGURE 20–3.Anteroposterior (A) and lateral (B) radiographs of untreated malleolar fractures resulting in dislocation of prosthesis.
Impingement
FIGURE 20–4.Impingement of the cut surface of the talus on the tibial component as a result of settling of the talar component.
recorded, bone should next be removed from the medial and lateral gutters of the ankle to permit increased clearance between the tibial component’s pillars and the uncovered portions of the talus. Before completing this procedure, the ankle should dorsiflex to at least 5 degrees past neutral. If this is not possible, consideration should be given to lengthening the Achilles tendon at its musculotendinous junction (Strayer procedure).
Aftercare consists of early weight-bearing in an off-the- shelf boot and early range of motion. Typically the patient
will benefit from 4 weeks of physical therapy, mainly to restore motion and balance. The boot can be discarded at the end of the month.
Syndesmotic Nonunion
One of the unique attributes of the Agility prosthesis is sta- bility against valgus collapse, obtained by the tibial compo- nent because its lateral edge is supported by the medial cortex of the fibula. To maintain this position, a distal tibia/
fibula and/or a syndesmotic fusion must be obtained. This is accomplished with the use of autograft from the cut sur- faces and two 4.0-mm cancellous syndesmotic screws placed in a lag mode across all four cortices. Many surgeons have elected to add a lateral plate to help secure the fusion during the initial procedure, but this is a misunderstanding of the technique. Originally, the cuts often resulted in notching of the fibula shaft with subsequent fracture, requiring plating to secure the broken fibula. This problem has been solved by placing cannulated 4.0-mm cancellous screws (40 mm in length) into each malleolus prophylactically before the pro- cedure is formally started. Unless the fibula shaft is so osteo- porotic that isolated screws tear through the lateral cortex, a lateral plate is contraindicated, as it is bulky and painful and does not aid in syndesmotic fusion at all.
Unfortunately, despite all these techniques, approxi- mately 10% to 15% of cases may present with a syndesmotic nonunion (Fig. 20–8). Radiographic findings of widening between the tibia and fibula are suspicious for a syndesmotic nonunion. Syndesmotic screws will be loose, and invariably the tibial component will have tilted into valgus, with a space evident between the lateral edge of the tibial tray and the medial cut surface of the fibula on x-ray examination.
An early nonunion occurs in the immediate postoperative period, generally within the first 12 weeks. Importantly, at this early point the tibial component has not shifted and a simple revision of the fusion is possible. If the syndesmotic nonunion FIGURE 20–5.Arthroscopic view of severe overgrowth. Note the
almost complete fibrous covering of the talar component.
FIGURE 20–6.Intraoperative determination of a loose talar component after simple evaluation with a Freer elevator.
FIGURE 20–7.Undersurface of talus showing lack of in-growth (arrow).
181 C H A P T E R20 Recognition and Salvage of the Failed Ankle Replacement Arthroplasty
is diagnosed after the patient has begun walking, then tibial tray loosening and/or valgus erosion of the lateral tibia will be evident and component removal and revision will be needed.
Surgical Revision of a Syndesmotic Nonunion In performing this procedure, the surgeon should be aware that a complete revision of the components may be required.
The existing anterior midline approach should be reused.
Once the ankle joint is entered and the soft tissue removed from the nonunion site, the screws are partially backed out percutaneously if they are not loose. If loose, they should be completely removed. A laminar spreader is used to con- firm the failure of the fusion mass to consolidate. Once the nonunion is identified, the tibial component is gently pried at the tibial metal–bone interface, to determine loosening.
The surgeon should avoid using excessive force, as this will dislodge the prosthesis. Although slight motion may be noted, the tibial component should remain in place with this maneuver. If a syndesmotic nonunion exists and the tibial component is secure, revision should proceed.
With the laminar spreader in place, a high-speed bur is used to create bleeding bone surfaces along the lateral tibial and medial fibular cortices. A structural block of cancellous allograft bone should be fashioned to fit between the bleed- ing surfaces of the tibia and fibula, at the level of the syndes- mosis. If this bone block is placed too close to the level of the joint, it will push the fibula away from the tibia and create an unacceptable gap between the lateral malleolus and the lat- eral edge of the prosthesis. Once correctly placed, a large fragment bone reduction clamp is used to compress together
the tibia and fibula so that the lateral surface of the metal tibial tray is abutting the medial cut surface of the fibula.
Under fluoroscopic control, either the existing screws are reinserted or new screws are inserted using the original holes in the fibula, percutaneously. If this is not possible because of bone fatigue, a small lateral incision must be made, and a three-hole, one-third tubular plate is used as a lateral cortex to help hold the screws in the proximal and dis- tal holes of the plate. The screws should be noncannulated 3.5-mm cortical screws or 4.0-mm fully threaded cancellous screws, placed in a lag mode using all four cortices.
After the syndesmosis has been refused, the fibula shaft should be osteotomized to allow healing to occur without stress. The fibula just above the proximal screw should be freed of soft tissue through the anterior incision. Using a small saw blade, an oblique fibular osteotomy is performed so that the proximal fibular shaft is trapped by the cut surface of the distal shaft (Fig. 20–9). Wound closure is standard.
Aftercare includes placing the patient in a non–weight- bearing cast in the neutral position until the fusion is healed on radiographs. This is seen as bridging trabeculae across the tibia and fibula on radiography and generally takes between 10 and 12 weeks. Once healed, weight-bearing to tolerance is permitted.
Revision of Components
The most difficult situation in total ankle surgery is the deci- sion to revise one or more components. This may or may not be possible. The patient must be made aware of the fact that surgical options may require revision, conversion to a long stem talar prosthesis, or ankle and subtalar fusion. Although the principal goal should be to relieve the patient of pain, and to spare the subtalar joint complex, a revision, whether with a custom stemmed talar prosthesis or a fusion may require crossing the subtalar joint to find bony stability. Finally, the surgeon must always be aware of the possibility of an FIGURE 20–8.Syndesmotic nonunion.
Oblique osteotomy
Malleolar screw
FIGURE 20–9.Treatment of nonunion with an oblique fibular osteotomy. Note malleolar screws placed prophylactically to prevent intraoperative fracture.
infection, encountered during the procedure. As this will immediately change the treatment plan, the patient should be made aware of this fact preoperatively as well.
Tibial Component
If the tibial component is loose and the syndesmosis is healed, there is no way at the present time to remove the prosthesis without taking the talar component out, even if it is stable.
If the tibial component is loose without erosion of the tibia, both components should be removed and a new, larger total ankle should be inserted using standard methods. If erosion of the tibia is evident, then structural iliac crest bone graft must be obtained to allow repositioning of the implant (Fig. 20–10).
Allograft is not acceptable as no in-growth will occur into a dead piece of bone, and this will ultimately cause loosening of the prosthesis again. If excessive erosion is evident on preoperative films, consideration for a fusion must be given.
Talar Component Loosening
In the author’s experience, the most common cause of an Agil- ity Total Ankle failure is talar component loosening due to the original design of the talar prosthesis. If the talar component is malaligned or grossly loose, it will simply fall out of the talus when gentle pressure is applied. Almost all loose talar components are associated with some degree of settling.
Unless the talus is fractured, the component will continue to settle until its inferior fin comes into contact with the sub- chondral bone of the posterior facet of the talus, at which
point it will stop. The component will then “windshield wiper” in a side-to-side motion, creating a wider fin slot in the medial-to-lateral direction, further eroding the talus.
Newer designs, most notably the LP design, appear to resolve these problems. When simply revising an older component, exchange to a newer LP talus should be performed.
When removing the talar component, care must be taken to avoid prying against a stable tibial component and loosening it. If the polyethylene component is in the way, it should be removed. If the polyethylene insert is difficult to remove, an osteotome should be used to split the insert.
The talar surface is then cleaned of bone debris, osteophytes, and fibrous tissue. The talus is then repositioned using the external fixator so that it is parallel to the tibial tray. The cut surface of the talus may have to be recut to accomplish this, and this may require a freehand cut using a sagittal saw. The fin slot should be very carefully prepared, with great care taken to minimize additional bone removal. No graft is used on the talar side because it cannot develop in- growth at the bone–bone and bone–metal interface quickly enough to guarantee component stabilization.
A þ2-mm poly insert trial and aþ2-mm LP talar trial component are now inserted. This will add 4 mm to the arthro- plasty and suffices in restoring the loss of height due to the settling of the talar component. The surgeon must also con- firm the rotational position of the talus relative to the tibia, as well as to the foot. All gutters must be cleaned of bone, and this is most often performed using a reciprocating saw to remove the medial and lateral edge of the remaining talar surface to prevent impingement, once the trials have been removed.
When ready to implant, the tibial polyethylene insert is placed into the tibial tray. The LP talar component is then inserted. The external fixator may have to be removed to allow maximum plantarflexion to insert the talus. Once the talus is seated, it should be evaluated for stability. If the com- ponent is deemed stable, standard closure and splinting is performed. Throughout, tourniquet time should not exceed 150 minutes.
Aftercare requires that the patient be placed in a short leg weight-bearing cast. The patient is instructed to remain non–weight-bearing for at least 6 weeks, except for 10 min- utes each morning and evening. During this time, the patient stands with his or her weight evenly distributed on both legs.
Rocking, single leg stance, and ambulation are strictly avoided. Stitches are removed at 6 weeks and the patient is placed into an off-the-shelf removable boot at this time, and partial weight-bearing is begun in the boot with either crutches or a walker. The patient should be able to begin unsupported weight-bearing by 12 weeks based on fluoro- scopically controlled, radiographic evidence of healing across the bone–implant interface.
Custom Stemmed Talar Prosthesis
When the talus is so eroded or damaged that a simple revi- sion cannot be performed, until recently, the surgeon was left with fusion as the only other treatment option. Over the past Graft
FIGURE 20–10.Revision of a tibial component using autograft and an antiglide plate to secure it.
183 C H A P T E R20 Recognition and Salvage of the Failed Ankle Replacement Arthroplasty
3 years, stemmed talar components have been made available on a custom basis (Figs. 20–11 and 20–12). These one-piece devices have been devised to allow the prosthesis to receive additional stability through purchase in the calcaneus. While
this necessarily damages the subtalar joint, it should be clear that this joint is already severely damaged at the time of revi- sion ankle arthroplasty. In our experience with 19 such cases with a minimum 2-year follow-up, a statistically significant
A B
FIGURE 20–11.(A) AP and (B) lateral radiographs of a failed total ankle. Note that both components have shifted and are loose.
A B
FIGURE 20–12.Anteroposterior (A) and lateral (B) radiographs 2 years after revision total ankle replacement and insertion of a custom stemmed talar component. There has been no subsidence of the talar component.
functional improvement and decrease in pain were seen in all patients. Also, in 16 patients, there was no talar component subsidence, whereas in 3 patients, subsidence was less than 3 mm.
When evaluating the patient with a failed talar compo- nent, radiographs showing severe talar erosion and compo- nent collapse suggest the need for a stemmed component to avoid the need for a double hindfoot fusion (ankle and subtalar joints). Although CT scans will have significant arti- fact at the ankle, they will be helpful in this case to assess the damage to the subtalar joint. Once a surgeon has decided that a revision to a long stem is an option for the patient, plain radiographs with magnification markers are obtained.
At this point, the surgeon may write a prescription for a unique custom implant for the patient, and a custom pros- thesis and trial will be manufactured. Insertion of this device is beyond the scope of this text, but either surgeons experi- enced in this technique should be consulted or the patient should be sent to such a center for revision.
Revision to a Double Hindfoot Ankle and Subtalar Arthrodesis
Most patients who have a failed prosthesis and are not candi- dates for revision due to loss of bone, or those who simply do not wish to continue to undergo surgery, are candidates for a double hindfoot fusion using a femoral head allograft and a retrograde hindfoot nail (Figs. 20–13 and 20–14).
After exsanguination and inflation of the tourniquet to 350 mm Hg, the ankle is opened through the original inci- sion and the prosthesis is removed. A laminar spreader is placed into the defect, and using lateral fluoroscopic control, correct tension can be determined. An acetabular reamer is placed into the empty space until the best-fit diameter is selected. A fresh-frozen allograft femoral head of similar diameter is then selected and placed in normal saline to thaw.
At the same time, platelet-rich plasma is obtained. Reaming is performed such that a sphere-shaped defect is made in the space previously occupied by the implants, and the
FIGURE 20–13.The patient inFigure 20–3was revised to a double hindfoot fusion using femoral head allograft and a retrograde nail.
185 C H A P T E R20 Recognition and Salvage of the Failed Ankle Replacement Arthroplasty
femoral head is trialed in this space. The allograft can be fur- ther shaped to fit, with the femoral neck portion facing ante- rior. This should be cut flush with the anterior cortex of the distal tibia. Once satisfied that the fit is correct, the allograft is soaked with platelet-rich plasma until it percolates through the graft. The slurry of bone graft is then applied to all the raw bone surfaces and ankle joint. Platelet-rich plasma is injected into this area again as well. The femoral head inter- positional allograft is then inserted, and position and align- ment are verified using intraoperative fluoroscopy.
With the C-arm in the lateral position, a guide pin is placed into the lateral plantar aspect of the calcaneus until it was in line with the medullary canal of the tibia. Similar alignment is verified on the AP view. While the steps of insertion vary between nail manufacturers, an important requirement of the procedure is that the assistant holds the
graft with a bone clamp to prevent it from rotating or shift- ing during reaming. Once this is performed, the nail is inserted and distally locked. It should then be impacted and locked proximally using a dynamic slot screw. The fibula may be lagged into the tibia, or the graft at the surgeon’s dis- cretion. The reminder of the graft and platelet-rich plasma are applied and the wound is closed in a standard manner.
No drain is used, to prevent loss of the platelet-rich plasma.
Standard closure is performed. The tourniquet is removed and a splint is applied.
Aftercare includes casting and non–weight-bearing for 12 weeks until evidence of fusion is observed. Stitches are usu- ally removed at 6 weeks. Therapy and progressive weight- bearing in an off-the-shelf boot may be begun at 12 weeks.
The patient should be back to activities of daily living by 14 weeks postoperative.
FIGURE 20–14.Final radiographs at 2 years showing complete consolidation of the allograft. The patient has done very well and walks without ambulatory aids.