Michel Bonnin, Brian Donley, Thierry Judet, and Jean-Alain Colombier
DEFINITION
The Salto Total Ankle Prosthesis is a cementless resurfacingtype implant that is intended to restore near-normal joint kinematics. Fixation is achieved through bone ingrowth.
The surgical technique is critical to a successful outcome, and some criteria are essential:
Tight fit of the components and extended contact area with bone to achieve good primary stability, which is a prerequisite for secondary biological fixation
Restoration of the mechanical axis of the ankle
Accurate restoration of the joint line (proper level and strict horizontal plane)
Preservation or restoration of the soft-tissue balance
Adequate soft tissue release to achieve good range of motion (ROM) intraoperatively
ANATOMY
The Mobile-Bearing Salto Prosthesis
The Salto Total Ankle Prosthesis (Tornier SA, SaintIsmier, France) was developed between 1994 and 1996 and has been used clinically since January 1997.
FIG 1 • A. An oblique view shows the Salto Total Ankle Prosthesis. B. An AP view shows the three main components and the malleolar component.
___________
Dr. Donley is a paid consultant for Tonnier, Inc., the company that makes the Salto Talaris Anatomic Ankle.
Based on experience with the third-generation cementless meniscal-bearing designs, this system was designed to restore nearly normal kinematics of the ankle (FIGS 1 AND 2).
A dedicated instrument system was developed to achieve optimal positioning of the components, and the design of the implant was optimized to better restore the natural anatomy and obtain an optimal primary fixation of the components while retaining a minimally invasive resurfacing concept.
The tibial component accommodates the superior flat surface of the mobile bearing. Its smooth surface allows free translation and rotation of the mobile bearing. The 3-mm medial rim protects the polyethylene from impingement with the medial malleolus.
The specific shape (segment of a cone of revolution) of the talar component replicates the anatomy of the talar dome. It is broader anteriorly than posteriorly, and the lateral condyle has a larger radius of curvature than the medial condyle. As a result, the axis of flexion and extension of the talar component, under the polyethylene, is aligned with the physiologic axis. The lateral aspect of the talus is resurfaced, allowing articulation with the lateral malleolus.
The ultra-high-molecular-weight polyethylene (UHMWPE) insert articulates with the tibial component superiorly and with the talar component inferiorly. It maintains full congruency with the talar component in flexion and extension and accommodates as much as 4 degrees of varus and valgus in the coronal plane, thereby reducing the chance of polyethylene edge loading.
The tibial component is available in three sizes and the talar component is available in four sizes. The mobile bearing is size-matched to the talar component in thicknesses from 4 to 8 mm.
The mobile-bearing size must match the size of the talar component. The talar component must be equal to or one size less than the tibial component.
FIG 2 • AP (A) and lateral (B) radiographs show the Salto Total Ankle Prosthesis in situ.
FIG 3 • The Salto-Talaris components and instrument system are the same as those of the Salto prosthesis, except that the tibial component is a fixed-bearing design.
Primary fixation to the tibia is ensured by close match of the tibial component to the epiphysis, and enhanced by an AP keel and a tapered cylindrical plug.
Stability of the talar component is provided by three bone cuts, and insertion of an 11-mm-diameter hollow fixation peg into the body of the talus.
Secondary fixation is provided by bone ingrowth into a dual coating of hydroxyapatite applied to a 200-µm-thick layer of plasma-sprayed titanium.
The Fixed-Bearing Salto-Talaris Prosthesis
Our experience with the Salto prosthesis has led us to revise our concept of mobility. As a matter of fact, owing to the anatomic design of the implant, the precision of the bone cuts, and the accuracy in component positioning, the need for and the potential problems associated with postoperative motion of the polyethylene bearing during flexion–extension movements have been almost completely eliminated. This has been confirmed in clinical studies based on standing dynamic views. On the other hand, intraoperative motion of the tibial component assembly is most helpful in allowing self-positioning of the bearing with respect to the talar component before the tibial keel preparation is completed.
The Salto-Talaris components and instrument system are the same as those of the Salto prosthesis, except that the tibial component is a fixed-bearing design (FIG 3). The final position of the tibial component is fine-tuned at the end of the procedure to achieve perfect alignment with the talar component. In this manner the self-positioning feature of the mobilebearing insert has been retained.
PATHOGENESIS
In general, our indications for total ankle arthroplasty (TAA) are: end-stage ankle osteoarthritis (OA) or rheumatoid arthritis (RA).
In OA, degeneration may be due to sequelae of trauma, chronic ankle instability, and rarely primary osteoarthritis.
In our experience, RA occurs relatively infrequently in the ankle when compared to the hip or knee. However, there is no consensus on the actual rate of ankle joint involvement in RA patients, with figures ranging from 9% in the study by Vainio,8 in which clinical criteria were used, to 40% in the study by Jakubowski et al,6 which employed radiographic criteria.
Occasionally, end-stage erosive or degenerative changes of the ankle may develop secondary to osteochondromatosis, pigmented villonodular synovitis, hemochromatosis, or osteochondritis dissecans.
Ankle joint involvement in RA tends to occur late in the disease process, with symptoms not occurring until a mean disease duration of 17 to 19 years.
Since the tibiotalar joint is rarely affected in isolation, treatment will need to be systemic and not only for the ankle.
NATURAL HISTORY
Progressive tibiotalar arthritis typically is accompanied by progressive ankle stiffness. Loss of ankle ROM, particularly dorsiflexion, results from tibiotalar osteophytes and less resilience in the distal tibiofibular syndesmosis.
Over time, the patient may develop an equinus gait with resultant Achilles tendon contracture, posterior capsular adhesions, and occasionally tibialis posterior adhesions.
PATIENT HISTORY AND PHYSICAL FINDINGS
Methods for Examining the Degenerative Ankle Joint
Silfverskiold test
Passive ankle ROM with the patient supine and the knee flexed and extended
Physiologic ROM with this examination is 15 (dorsiflexion)/ 0/40 (plantarflexion).
An isolated gastrocnemius contracture is present when lack of dorsiflexion with the knee in extension is eliminated with knee flexion.
Evaluation of ankle ROM with the patient standing and walking
Visualizing the gait pattern. The patient may externally rotate the extremity, or female patients may be able to walk in high heels to mask the lack of ankle dorsiflexion.
Hindfoot ROM
We use three grades of hindfoot motion: physiologic, diminished, or stiff. We favor total ankle arthroplasty (TAA) over ankle arthrodesis in patients with a stiff hindfoot.
Hindfoot alignment with the patient standing or ambulating
Hindfoot malalignment (varus or greater than physiologic valgus) may be most pronounced with the patient walking.
Hindfoot alignment with the patient supine
We typically assess passive hindfoot motion to determine if the deformity can be reduced to a physiologic position. In our hands, this examination determines the type of hindfoot realignment that will be performed concomitant to TAA.
Tibiotalar instability
The examiner successively assesses coronal plane and sagittal plane stability with varus–valgus stress and anterior drawer testing, respectively. In our hands, varus instability or fixed varus ankle requires careful ligament balancing.
IMAGING AND OTHER DIAGNOSTIC STUDIES
In our preoperative assessment we not only determine the extent of deformity and instability at the ankle but also assess any concomitant ipsilateral lower extremity malalignment that may have a bearing on the outcome of TAA. We routinely obtain weight-bearing AP, mortise, and lateral radiographs of both ankles; radiographs of the uninvolved ankle typically provide some understanding of what is physiologic for the patient. Weight-bearing mechanical axis hip-to-ankle radiographs are required if there is associated deformity of the ipsilateral lower extremity.
We recommend obtaining CT scans of the ankle and hindfoot, particularly to review coronal sections, to further evaluate tibial or talar bone loss or cysts not fully defined on plain radiographs.
DIFFERENTIAL DIAGNOSIS
Septic arthritis
Charcot neuroarthropathy
NONOPERATIVE MANAGEMENT
We have had limited success with nonoperative management in active patients with end-stage ankle arthritis.
Activity modification, rocker-bottom shoe modification, and bracing offer some relief.
We reserve nonoperative management for low-demand patients who are poor surgical candidates.
SURGICAL MANAGEMENT
Total Ankle Arthroplasty Versus Ankle Arthrodesis
In general, arthrodesis is favored over TAA because:
Lower risk of mechanical implant failure; no risk of implant wear
Lower risk of infection
Less chance of skin necrosis when the ankle has been previously operated on
In our hands, lower incidence of residual pain
In general, TAA is favored over ankle arthrodesis because:
Less risk of developing adjacent (hindfoot) joint arthritis
In our hands, more favorable functional outcome
In our opinion, malunion or development of adjacent joint arthritis makes revision surgery more difficult after arthrodesis.
Preoperative Planning
Preoperative evaluation of weight-bearing radiographs and CT scan to:
Choose the optimal implant size, with the use of available templates. This is important because an oversized prosthesis will alter the center of rotation, giving rise to pain and stiffness.
If the talus is particularly deformed, the template should be applied to the contralateral, unaffected ankle.
Determine the reference for establishing the ideal tibial resection level, taking into account the extent of wear in the tibial plafond
Analyze tibiotalar joint alignment relative to the tibial shaft axis. This allows differentiation between axial deviations:
Resulting from asymmetrical wear of the tibial plafond that may be corrected with tibial preparation.
Because of malunion that may require corrective osteotomy, simultaneous to or staged with TAA.
Analyze the residual talar body.
Asymmetry needs to be balanced in the talar preparation.
Evaluate the hindfoot.
A joint-sparing calcaneal osteotomy may be necessary to realign the hindfoot.
In the face of hindfoot arthritis or hindfoot instability, a subtalar or even triple arthrodesis may be warranted.
Positioning
The patient is positioned supine on the operating table, with a pad under the ipsilateral hip to promote a neutral tibial and foot alignment with the foot pointing to the ceiling.
The plantar aspect of the foot should be flush with the end of the table.
Placing a rolled towel under the ankle facilitates subtle adjustments in ankle positioning.
We routinely use a thigh tourniquet.
In our experience, a pillow placed behind the knee allows the Achilles tendon to relax and may improve exposure.
We recommend including the knee in the sterile field so that the limb can be positioned more freely and so that the patella and tibial tubercle may be used to confirm optimal alignment. The surgeon stands at the foot of the table, with the assistant at the lateral side of the operative leg.
Approach
The tibiotalar joint is approached through an anterior midline incision starting 8 to 10 cm proximal to the joint line and extending to the midfoot.
The soft tissues must be handled carefully, especially in patients being managed with systemic steroid treatment.
The surgeon should avoid undermining the skin.
The surgeon should maintain deep retraction only and avoid tension directly on the skin edges.
Extending the skin incision will further diminish skin tension.
While we maintain meticulous hemostasis, we ligate vessels whenever possible and use electrocautery sparingly to diminish the risk of skin burns. We typically incise the crural fascia and extensor retinaculum along the lateral border of the tibialis anterior tendon, using the interval between the tibialis anterior and extensor hallucis longus tendons.
Whenever possible, the tibialis anterior tendon should remain protected in its individual sheath throughout the procedure (this also separates the tendon from the anterior incision during closure).
Alternatively, the extensor retinaculum may be incised at the lateral border of the extensor hallucis longus tendon, using the interval between the extensor hallucis and extensor digitorum longus tendons. The tendons are retracted with angled retractors, and the deep neurovascular bundle (anterior tibial artery and deep peroneal nerve) is identified in the proximal wound and carefully reflected laterally.
The periosteum and joint capsule are incised longitudinally. The medial and lateral flaps are elevated using a scalpel and an elevator to expose the tibiotalar joint to the anterior margins of the malleoli.
To avoid direct tension on the skin margins, we use deep retractors, one at the proximal aspects of each malleolus.
Anterior osteophytes are removed with an osteotome, and the talar facets are cleared with a rongeur.
We then define the physiologic aspects of both malleoli, removing any osteophytes, ossifications, and loose bodies that obscure visualization of the medial and lateral ankle gutters, distort the natural anatomy, or impinge on the talus (FIG 4).
Upon completion of these steps, the talus should be mobile and the medial and lateral gutters should be fully exposed.
FIG 4 • A lateral retractor is placed against the lateral malleolus and a medial retractor against the upper part of the medial malleolus. Anterior osteophytes are removed with an osteotome, and the talar facets are cleared with a rongeur.
TECHNIQUES
TIBIAL RESECTION
The goal is to restore a physiologic tibiocalcaneal axis. Ideally, implant position should produce a joint line at right angles to the mechanical tibial axis in the coronal plane and reproduce the physiologic 7-degree posterior slope in the sagittal plane.
Align the extramedullary guide with the anterior tibial crest or a line joining the center of the knee and the midpoint of the distal tibial surface.
Proximally, secure the alignment guide to the anterior tibial tuberosity with a self-drilling pin, roughly perpendicular (in the sagittal plane) to the malleolar tips and distal medial tibial metaphysis in the sagittal plane (TECH FIG 1).
We then perform five sequential adjustments.
Orientation in the Coronal Plane
Provided there is anatomic or near-anatomic overall alignment of the lower extremity, the tibial cut should be horizontal and perpendicular to the tibial axis (TECH FIG 2).
Perform resection using the extramedullary guide referencing off the anterior tibial border.
A few degrees of coronal plane deviation proximal to the ankle or at the knee is readily compensated by realigning the proximal aspect of the external tibial alignment guide on the pin placed in the tibial tubercle. However, in our experience moderate to severe deformity proximal to the ankle should be corrected before TAA, typically in a staged fashion.
TECH FIG 1 • A, B. Left ankle. The extramedullary guide is aligned with the anterior tibial crest. It is attached with self-drilling pins at the anterior tibial tuberosity, roughly perpendicular (in the sagittal plane) to the malleolar tips, and then at the distal medial metaphysis of the tibia. Resection is performed using the extramedullary guide, referencing off the anterior tibial border. A few degrees of axial deviation of the knee joint in the coronal plane can be compensated for by using the proximal holes (arrow) to obtain a perfect adjustment and to perform a bone cut that will be almost horizontal.
TECH FIG 2 • In the coronal plane, provided there is a good overall alignment of the lower extremity, the tibial cut should be horizontal and perpendicular to the tibial axis.
Orientation in Rotation
The external tibial alignment guide, when positioned parallel to the anterior tibial cortex, establishes a physiologic posterior slope of 7 degrees for the tibial cut.
In our experience, to achieve correct angulation of the tibial cutting block, the extramedullary guide must rest on the tibia at both the proximal and distal ends.
Resection Level
The goal is to restore an anatomic joint line level. When the subchondral architecture of the tibial plafond is intact, the amount of distal tibial resection should match the metal tibial base plate plus the polyethylene insert.
We use the apex of the tibial plafond as the reference point for tibial resection. To expose this apex, we resect the anterior margin of the tibial plafond using an osteotome. With clinical inspection or fluoroscopic confirmation in the sagittal plane, the resection level is determined from this reference point (TECH FIG 3).
For the Salto (three-part mobile-bearing) prosthesis, the tibial resection is 7 mm (3 mm for the thickness of the metal base plate plus 4 mm for the minimum thickness of the polyethylene).
For the Salto-Talaris (two-part fixed-bearing) prosthesis, the minimum resection is 8 mm (3 mm for the thickness of the metal base plate plus 5 mm for the minimum thickness of the polyethylene). However, as a routine we resect 9 mm, which allows for downsizing of the polyethylene in the event that the joint is too tight.
We modify the tibial cut based on the ligamentous tension in the ankle. In stiff ankles, we typically resect 2 mm more than the minimal resection; in ankles with instability, we generally resect 2 mm less than the minimal resection.
Bone loss in the tibia may warrant adjusting the tibial cut to re-establish the proper joint line.
Orientation in the Sagittal Plane
Since both the tibial and initial talar cutting guides are suspended from the tibial alignment guide, thus linking the tibial and initial talar resection, proper rotational alignment is critical. Malrotation of the components may interfere with the implant's kinematics, create malleola impingement, risk edge loading, and (particularly in the fixed-bearing Salto-Talaris) lead to increased constraint (TECH FIG 4).
TECH FIG 3 • A. The goal with the Salto is to restore an anatomic joint line level. Then, in the absence of significant bone wear, the amount of bone resection on the tibia must fit exactly with the thickness of the tibial components (metal base plate plus polyethylene). B. The only reliable landmark is the plafond of the tibial pilon. The anterior margin of the tibial pilon is resected using an osteotome. This will provide direct exposure of the joint surface. From this reference level, the required cut is determined, aiming to remove as little bone as possible. C. The guide is adjusted at the level of the tibial pilon (small arrow) and this level is observed on the scale on the tibial alignment jig (large arrow and circle). Left ankle. D. Then, from the initial reference position the guide is adjusted proximally from 7 to 9 mm according to the desired amount of resection (arrow and circle). Left ankle.
While the mobile-bearing Salto implant may compensate for a certain degree of malpositioning, edge loading or overhang of the polyethylene on the metal tibial tray may result. Therefore, every effort should be made to orient the implant on the center bisecting line of the talus in the coronal plane, the line that is parallel with the talus when it is taken through its motion arc. We rotate the cutting guide until it is centered on the line bisecting the space between the medial and lateral talar facets.
Orienting the implant in line with the second metatarsal may be useful but introduces errors with associated midfoot or forefoot deformity.
Coronal Plane Positioning
The final adjustment is to center the cutting block on the tibial plafond, often necessitating medial or lateral translation of the cutting block relative to the tibial alignment guide. The proper-size cutting block must be selected; the reference landmarks for sizing are the medial axilla and the lateral edge of the tibia.
Set the guide to avoid compromise of the malleoli. Secure pins within the cutting block at the level of resection to protect the malleoli from inadvertent saw blade excursion. (TECH FIG 5A).
Bone resection
Before making the sagittal bone cuts (medial and lateral), drill holes through the appropriate-size cutting block and fully insert two short pins through the superior holes to protect the malleoli during resection. Before placing the protective pins, an AP radiograph may be obtained to confirm proper position and sizing of the cutting block in the coronal plane.
For a mobile-bearing Salto prosthesis, use the extramedullary guide to initially prepare for the tibial keel as it sets the rotational alignment of the tibial component.
When implanting a Salto-Talaris prosthesis, the rotational alignment is established using the trials and ranging the ankle to allow the tibial base and insert assembly to self-center with respect to the trial talar component.
The capture guide on the cutting block guides the saw blade.
The tibial resection must be completed through the posterior cortex of the distal tibia, without plunging the saw blade into the posterior soft tissues.
We typically use a saw blade of adequate length and limited excursion.
Removing the resected bone
Remove the tibial cutting block but leave the external tibial alignment guide in position.
With a thin osteotome or small reciprocating saw, complete the two sagittal cuts through the predrilled holes created using the cutting block.
Remove the resected bone wafer.
The resected bone must be fully mobilized before attempting to extract it from the joint; abrupt mobilization of this bone may result in a fracture of the medial malleolus if the cut is not complete, especially in an ankle with an equinus contracture. The removal of the distal tibial resection is rarely done in one piece; usually piecemeal removal is required.
TECH FIG 4 • The rotational alignment is of critical importance even more so as the tibial and talar resections are linked. A. The talar component must be aligned with the axis of the talar dome (1) and is centered on the line bisecting the space between the medial and lateral talar facets (2 and 3). External (B) or internal (C) rotational malpositioning of the components will result in increased stress being placed on the fixation system, impingement with the malleoli and may interfere with the kinematics of the joint replacement.
Remove the anterior half. With the Salto and SaltoTalaris prostheses removal of the posterior portion may be delayed until after the posterior talar cut is completed (TECH FIG 5B).
TECH FIG 5 • A. The instrument system provides accurate component positioning through adjustment of the resection level, translation, and rotation. Pins can be inserted in the medial and lateral holes of the guide to visualize the limits of the tibial cut with respect to the malleoli. Before the tibial cut is performed, holes are drilled through the appropriate-size cutting block, and two short pins are fully inserted through the superior holes to protect the malleoli during resection (small arrows). B. The removal of the distal tibial resection is rarely done in one piece; usually, piecemeal removal is required. The anterior half is removed, and then removal of the posterior portion can be delayed until after the posterior talar cut is completed.
TALAR PREPARATION
Talar preparation requires that the ankle can be dorsiflexed to at least 90 degrees.
This angle is almost always obtained at this stage, since the removal of bone from the tibia (anterior part of tibial resection) will have created more space, even in a stiff ankle.
In the rare case that it is not achieved, then an Achilles tendon lengthening or gastrocnemius–soleus recession may need to be considered.
Talar preparation comprises three cuts: posterior, anterior, and lateral. The native medial talar dome is left intact with this technique.
Posterior Talar Chamfer Cut
To position the talar component properly on the prepared talar dome, the posterior talar cut must be inclined 20 degrees posteriorly.
With the ankle maintained at 90 degrees of dorsiflexion and the hindfoot in physiologic valgus position, suspend the talar guide from the external tibial alignment guide and insert a pin into the talus (TECH FIG 6A).
This pin dictates the sagittal orientation of the talar component.
This reference pin must be placed with the ankle in a strictly neutral position between flexion and extension.
Excessive dorsiflexion will lead to anterior and flexed positioning of the talar component.
Excessive plantarflexion tilts the implant backward.
Secure the posterior chamfer talar cutting block on this reference pin.
Talar styli are available to determine the level for an anatomic resection that corresponds to the thickness of the talar component.
In case of severe flattening of the talar dome, this resection level may need to be adjusted. The talar resection level depends on having satisfactory fixation of the implant in healthy bone while simultaneously trying to preserve as much talar bone stock as possible.
The posterior chamfer cut of the talus should be anatomic, parallel to the superior margin of the talar dome.
Asymmetric wear must be recognized and the posterior talar chamfer cut adjusted appropriately; shims are available to make such adjustments.
We do not recommend compensating extra-articular or hindfoot deformity by means of an asymmetric posterior talar chamfer cut; instead, simultaneous or staged hindfoot correction should be performed.
The talar guide orients the placement of four pins in the talus that are then used to guide the talar resection. Maintain the oscillating saw flush with the dorsal aspects of the pins while protecting the malleoli from injury (TECH FIG 6B).
The residual tibial bone is relatively easy to extract at this point, along with the resected portion of talus. A lamina spreader without teeth, used judiciously, usually improves exposure.
TECH FIG 6 • A. The talar pin setting guide (large arrow) is positioned on the distal end of the tibial guide. With the ankle positioned in neutral flexion, a pin is inserted through the hole into the talus (small arrow) (left ankle). B. The pinguided resection is performed with an oscillating saw, taking care to keep the saw blade flat against the pin surface during resection.
Anterior Talar Chamfer Preparation
Anterior talar preparation contributes to the correct AP and rotational positioning of the talar component.
Perform the anterior chamfer cut with a milling device controlled by the anterior talar cutting guide, secured on the posterior resected surface (TECH FIG 7).
Adequate anterior resection is essential to avoid an anterior talar position relative to the tibia, a situation that may lead to increased anterior contact stresses and potential edge loading.
TECH FIG 7 • The anterior chamfer cut is performed with a end mill cutter controlled by the anterior talar cutting guide, which is positioned on the posterior resected surface.
In our experience, the threshold to deepen the anterior chamfer preparation should be low.
Removing anterior talar neck osteophytes allows the guide to be properly seated on the talus.
Appropriate anterior chamfer preparation is determined using the talar gauge.
With respect to rotation, the guide must be perfectly aligned with the axis of the talar body. The second metatarsal may be used as a reference provided there is no associated foot malalignment.
Lateral Chamfer and Talar Stem Preparation
Proper positioning is essential.
In the sagittal plane, the guide should be positioned flush with the two previously resected surfaces, with no anterior overhang.
In the horizontal plane, rotation is determined with reference to the axis of the talar body.
In the coronal plane, correct mediolateral position is referenced from the lateral margin of the prepared talar dome.
Once correctly positioned, pin the cutting guide to the bone.
First, prepare the talar stem recession using the bell saw. Then insert a dedicated metal peg into this prepared portion of talus to afford greater stability to the lateral talar chamfer cutting guide. Prepare the lateral chamfer using an oscillating or reciprocating saw.
INSERTION OF TRIAL COMPONENTS
The appropriate-size talar trial is that which provides good coverage of the talus in the mediolateral plane, without medial overhang.
The talar trial lacks the plasma spray coating and thus lacks the interference fit of the actual talar implant; therefore, the talar trial may appear loose. To determine optimal polyethylene thickness and ligament balance, the talar trial remains in situ during insertion of the tibial trials.
Insertion of tibial trials
Salto mobile-bearing prosthesis
Insert the selected trial tibial component flush with the bone cut; this will serve as a drill guide for creation of the press-fit hole for the tapered cylindrical plug.
Insert the mobile bearing. Bearing thickness is crucial to the stability of the implant. A bearing of correct thickness will need to be pushed rather than slipped into the joint.
Salto-Talaris fixed-bearing prosthesis
Push the trial tibial base and insert assembly into position; it is free to rotate relative to the tibia.
As the ankle is ranged from flexion to extension the tibial trial locates its ideal position and rotation with respect to the talus, unless the tibial trial has essentially the same dimensions as the prepared tibial surface.
When this automatic adjustment is obtained, the definitive position is determined.
Perform preparation for the press-fit hole for the tapered cylindrical plug as described above for the Salto prosthesis.
The use of a fixed or mobile bearing allows different sizes to be employed on the tibia and on the talus; when this option is being used, the choice of polyethylene size must be by the same size as the talar component.
Range the joint and check stability. The implant should be stable in the coronal plane, without any residual laxity; dorsiflexion greater than 10 degrees should be readily obtained.
INSERTION OF THE DEFINITIVE COMPONENTS
Insert the definitive components.
The prosthesis must have sound initial stability, indicating appropriate ligament balance.
Before impacting the components, any tibial or talar subchondral cysts or other bone defects may be filled with bone graft.
Insert the talar component first.
After inserting the tibial component, fill the anterior opening of the cortex with bone graft obtained from the bone cuts to prevent any ingress of joint fluid (TECH FIG 8), which may lead to osteolysis.
TECH FIG 8 • After insertion of the tibial component, the anterior opening of the cortex (A) is filled with bone graft obtained from the bone cuts to prevent any ingress of joint fluid (B).
CLOSURE
Since the skin over the ankle is very delicate, closure must be meticulous.
Close the wound over an intra-articular drain. Whenever possible, close the capsule with absorbable sutures.
Suture the fascia and retinaculum. Isolate the toe extensor tendons and particularly the tibialis anterior tendon from the fascial suture line.
Close the loose subcutaneous tissue and the skin with interrupted sutures.
Apply a below-knee plaster cast with the ankle in maximum dorsiflexion.
POSTOPERATIVE CARE
The drain is removed the day after the operation.
Once the swelling has subsided, a below-knee circular resin cast is applied.
As a rule, weight bearing may be resumed once the resin cast has been applied.
Patients who have undergone Achilles tendon lengthening will be non–weight-bearing for 3 weeks.
Where there has been a malleolar fracture, the period of non–weight-bearing will be 45 days.
The cast is removed after 45 days to prevent skin problems, and physiotherapy is commenced.
OUTCOMES
Bonnin et al4 reported the results of a consecutive series of their first 98 cases implanted between 1997 and 2000.
With a mean 35 months of follow-up (range 24 to 57 months), they reported two failures requiring conversion to ankle arthrodesis.
Reviewing the same consecutive series with a mean 6.4 years of follow-up (range 5 to 8.5), they reported five failures necessitating conversion into arthrodesis.3
The mean AOFAS ankle–hindfoot score preoperatively was 32.3 (SD 10) and 83.1 (SD16) at last follow-up. The mean ankle range of motion measured on dynamic radiographs improved from 15.2 degrees preoperatively (SD 10) to 28.3 degrees at follow-up (SD 7).
COMPLICATIONS
Technical difficulties in TAA may arise from a number of factors.
Failure to Re-establish the Physiologic Joint Line
The final level of the implant joint line will depend upon the level of the tibial cut.
The level is determined with reference to the preoperative radiographs. Depending on the status of the tibial plafond, the anatomy of the malleoli, and lateral talomalleolar congruency, four different patterns may be encountered (FIG 5):
FIG 5 • A, B. Ankle mortise intact, no asymmetrical wear of the tibial pilon. C, D. Ankle mortise intact, tibial pilon asymmetrically worn. E, F. Malleoli deformed, tibial pilon intact. G, H. Malleoli deformed, tibial pilon worn.
The ankle mortise is intact, with symmetric wear of the tibial plafond. The procedure should be a simple resurfacing, with the metal tibial component and polyethylene thickness replacing exactly what is resected.
The ankle mortise is intact, but the tibial plafond is asymmetrically worn. This pattern is seen in advanced RA, especially in the wake of long-term steroid therapy. In this case, a reasonable and balanced distal tibial resection level will need to be determined during preoperative planning.
The malleoli are deformed, but the tibial plafond is intact. In our experience, this deformity involves the lateral malleolus. This pattern is seen in RA with severe hindfoot valgus that has resulted in a fatigue fracture of the fibula. In this case, the lateral malleolus will need to be managed with malleolar osteotomy and plating before TAA.
The malleoli are deformed and the tibial plafond is worn or depressed. These cases will need to be managed with a combination of the principles discussed above: first, a normal ankle mortise pattern will have to be created, and then a resection level will need to be determined, taking into account the extent of loss of tibial bone stock.
Extra-articular Deformity
The physiologic ankle joint line is perpendicular to the axis of the tibia, and the hindfoot axis is in slight (5 to 10 degrees) valgus in relation to the tibial axis. To promote long-term implant survival, physiologic alignment will need to be restored.
Inserting a TAA prosthesis into a malaligned tibia or hindfoot is a recipe for early loosening and failure.
Correction of deformities may be difficult in sequelae of trauma or RA. Preoperative evaluation should allow the determination of whether these deformities have an intra-articular or extra-articular origin.
In our experience, most intra-articular deformities resulting from wear or laxity (including varus position caused by OA in chronic instability) can be corrected from within the joint with the prosthesis.
In contrast, most extra-articular deformities cannot be corrected from within the joint with the prosthesis and must be treated independently with supramalleolar osteotomy, performed either staged or simultaneous to TAA (FIG 6A).
In our opinion, hindfoot malalignment associated with arthritis must be corrected by doing a triple arthrodesis before TAA (FIG 6B).
FIG 6 • A. In case of tibial malunion, a correction via a supramalleolar osteotomy must be associated with the ankle prosthesis. B. In case of hindfoot deformity, a correction via a subtalar or triple arthrodesis or calcaneal osteotomy must be done in association with the ankle prosthesis.
We recommend performing staged triple arthrodesis and TAA to reduce the potential for skin problems and edema. In our hands, triple arthrodesis is usually done as a first-stage procedure 45 days before TAA, which avoids prolonged cast immobilization (FIG 7).
We perform the triple arthrodesis by what would be an extension of the anterior approach to the ankle to prepare the talonavicular joint and a limited lateral–subfibular approach to the subtalar joint. We avoid dissection under the talar head to minimize the risk of necrosis of the talar body.
Fixation is achieved using a talocalcaneal screw and two talonavicular and calcaneocuboid staples.
The TAA prosthesis must be positioned on a properly aligned hindfoot.
In RA patients with a valgus deformity and severe lateral bone loss, bone grafting is the rule. Graft material is harvested from a local donor site (bone slices taken from the midtarsal joint, sometimes bone material taken from the proximal tibial metaphysis) and in some cases from the ipsilateral iliac crest in case of severe deformity.
We stage the TAA 45 days after triple arthrodesis using the proximal extension of the same anterior approach. The talocalcaneal screw is removed.
Bone Loss
Implant fixation requires sufficient tibial and talar bone stock and an intact ankle mortise.
In RA patients or in posttraumatic OA, there may be major bone loss, and defects may have to be grafted. In particularly severe cases, TAA may be contraindicated.
Ankle Instability
OA secondary to chronic lateral laxity is technically challenging because the persistence of lateral laxity may cause rapid deterioration of the prosthesis.
In our experience, most cases can be balanced with TAA. We routinely restore the ankle's soft tissue balance with TAA and comprehensive soft tissue release on the concave side of the deformity.
Medial release in a varus deformity is challenging and involves the entire deltoid ligament, which is first released subperiosteally from its malleolar attachment and then detached from the talus. We have been satisfied with this balancing technique, which, in our hands, eliminates the need for the medial malleolar osteotomy technique to rebalance the deltoid ligament.
FIG 7 • Rheumatoid arthritis of the ankle, subtalar, and midtarsal joints, with valgus shift of the hindfoot causing a fatigue fracture of the lateral malleolus. A triple arthrodesis was done in association with lateral malleolus correction osteotomy. Forty-five days later, the total ankle prosthesis was implanted in a correctly aligned hindfoot. (From Bonnin M, Judet T, Colombier JA, et al. Mid-term results of the Salto total ankle prosthesis: report of 98 cases with minimum two years follow up. Clin Orthop Relat Res 2004;424:6–18.)
With comprehensive and satisfactory medial release, we rarely need to perform a ligament reconstruction on the convex side of the deformity. Occasionally, however, for severe varus malalignment, we need to perform a lateralizing and valgus-producing calcaneal osteotomy to further realign the hindfoot.
Ankle Stiffness
End-stage tibiotalar joint arthritis almost always leads to stiffness of the tibiotalar joint.
Stiffness with equinus deformity requires sequential steps to regain dorsiflexion, beginning with excision of anterior ossifications, then freeing of talomalleolar adhesions, and finally posterior capsulectomy from within the joint.
The use of a lamina spreader greatly facilitates capsulectomy. However, great caution should be used to avoid avulsion of the medial malleolus and accidental penetration of the prepared tibial surface.
In particular, the surgeon must make sure that complete capsulectomy is performed at the posteromedial corner, flush with the tibialis posterior tendon.
Freeing up adhesions to this tendon is important as they may cause postoperative pain, particularly in patients who have previously undergone a procedure through a posteromedial approach.
In this case, tenolysis of the tibialis posterior tendon with opening of its retinaculum through a limited posteromedial approach may be useful. This approach makes posterior capsular release and even repair of associated fissures much easier.
Lastly, contracture of the triceps surae and Achilles tendon is often responsible for a deficit of dorsiflexion. Therefore, lengthening should be considered whenever dorsiflexion is less than 10 degrees after insertion of the trials. Release of flexors may be achieved through either tendon lengthening or fasciotomy of the triceps surae.
Achilles tendon lengthening
This simple procedure has little influence on the postoperative course, but it is associated with long-term persistence of posterior discomfort and sometimes with permanent loss of plantarflexion strength and range of motion.
Lengthening technique consists of making two or three percutaneous staged incisions with a fine scalpel; each incision should involve slightly more than half of the tendon.
The most distal incision may be performed on either side, depending on the fibers to be lengthened—laterally for a valgus deformity in order to preserve varus-oriented fibers, and medially for a varus hindfoot.
While making incisions, the ankle should be held in forced dorsiflexion with the trial components in place. Dorsiflexion suddenly increases as fibers slide over one another (FIG 8).
Fasciotomy of the triceps surae usually does not cause postoperative pain; it is performed through a limited midline posterior approach at the middle third of the leg. The sural vein is preserved.
The insertional fascia of the gastrocnemius is sectioned in a V-shaped fashion, and the underlying soleus fascia is sectioned in line with the muscle fibers. The postoperative course is the same as for Achilles tendon lengthening.
Anterior Translation of Talus
Anterior translation of the talus must always be corrected to restore normal kinematics and avoid early wear due to overloading in a fixed-bearing prosthesis or due to overhanging of the polyethylene bearing in a mobile-bearing prosthesis (alignment between the polyethylene bearing and the talar component must be maintained at all times).
FIG 8 • Percutaneous lengthening of the Achilles tendon. Lengthening technique consists of making two or three percutaneous staged incisions with a fine scalpel; each incision should involve slightly more than half of the tendon.
Repositioning of the talar component requires complete soft tissue release (ie, talomalleolar compartment, posterior capsule) as well as correction of equinus deformity (if any) through Achilles tendon lengthening.
Should these procedures prove ineffective, the talar component will have to be moved posteriorly, which means recutting the anterior chamfer.
In our experience, the tibial component will have to be positioned as far anteriorly as possible beneath the distal tibia.
REFERENCES
· Bonnin M. La prothèse totale de cheville. Encycl Méd Chir (Editions scientifiques et médicales Elsevier Paris). Techniques Chirurgicales, Orthopédie Traumatologie, 44-903, 2002, 10p.
· Bonnin M, Bouysset M, Tebib J, et al. Total ankle replacement in rheumatoid arthritis: treatment strategy. In: Bouysset Y, Tourné K, Tillmann M, eds. Rheumatoid Arthritis: Foot and Ankle. Paris: Springer Verlag, 2006.
· Bonnin M, Judet T, Colombier JA, et al. Total Ankle Prosthesis: Fiveto Eight-Year Results. Presented at the 22nd Annual Summer Meeting of the AOFAS, La Jolla, Calif., July 14–16, 2006.
· Bonnin M, Judet T, Colombier JA, et al. Mid-term results of the Salto total ankle prosthesis: report of 98 cases with minimum two years follow up. Clin Orthop Relat Res 2004;424:6–18.
· Bonnin M, Judet T, Siguier T, et al. Total ankle replacement: history, evolution of concepts, design and surgical technique. In: Bouysset Y, Tourné K, Tillmann M, eds. Rheumatoid Arthritis: Foot and Ankle. Paris: Springer Verlag, 2006.
· Jakubowski S, Mohing W, Richter R. Operationen am rheumatischen Fuss. Therapiewoche 1970;20:762–768.
· Judet T, Piriou P, Elis JB, et al. Total-endoprothese des oberen Sprunggelenkes. Konzepte und Indikationen der Saltoprothese. In: Imhoff AB, Zollinger-Jies H, eds. Fußchirurgie. Stuttgart, New York: Georg Thieme Verlag, 2003.
· Vainio K. The rheumatoid foot: a clinical study with pathological and roentgenological comments. Ann Chir Gynaecol 1956;45(Suppl 1):1–12.
· Weber M, Bonnin M, Colombier JA, et al. Erste Ergebnisse der Salto-Sprunggelenkendopprotheseseine fränzösische Multizenterstudie mit 115 Implantaten. Fuβ Sprunggelenk 2004;2:29–37.