James K. DeOrio, Mark E. Easley, James A. Nunley II, and Mark A. Reiley
DEFINITION
The INBONE™ (Wright Medical, Memphis, TN) total ankle system, like other total ankle systems, is indicated for end-stage ankle arthritis failing to respond to nonoperative intervention.
In contrast to essentially all other total ankle systems, however, the INBONE™ total ankle system uses intramedullary rather than extramedullary referencing.
While the intramedullary alignment guide passes through the plantar foot, calcaneus, talus, and tibia, it does so anterior to the posterior facet of the calcaneus and does not violate any articulations of the subtalar joint.
To achieve reliable intramedullary alignment, the INBONE™ total ankle system uses a leg frame that is initially cumbersome, demands more pre-incision preparation, and requires greater fluoroscopy time than other total ankle systems. However, with experience this technique becomes manageable and allows the user to correct deformities prior to making bone cut.
ANATOMY
Ankle
Tibial plafond with medial malleolus
Articulations with dorsal and medial talus
In sagittal plane, slight posterior slope
In coronal plane, articular surface is 88 to 92 degrees relative to lateral tibial shaft axis.
Fibula
Articulation with lateral talus
Responsible for one sixth of axial load distribution of the ankle
Talus
60% of surface area covered by articular cartilage
Dual radius of curvature
Distal tibiofibular syndesmosis
Anterior inferior tibiofibular ligament
Interosseous membrane
Posterior tibiofibular ligament
Ankle functions as part of the ankle–hindfoot complex much like a mitered hinge.
PATHOGENESIS
Post-traumatic arthrosis
Most common cause
Intra-articular fracture
Ankle fracture-dislocation with malunion
Chronic ankle instability
Primary osteoarthrosis
Relatively rare compared to hip and knee arthrosis
Inflammatory arthropathy
Most commonly rheumatoid arthritis
Other
Hemochromatosis
Pigmented villonodular synovitis
Charcot neuroarthropathy
Septic arthritis
NATURAL HISTORY
Post-traumatic arthrosis
Malunion, chronic instability, intra-articular cartilage damage, or malalignment may lead to progressive articular cartilage wear.
Chronic lateral ankle instability may eventually be associated with:
Relative anterior subluxation of the talus
Varus tilt of the talus within the ankle mortise
Hindfoot varus position
Primary osteoarthrosis of the ankle is rare and poorly understood.
Inflammatory arthropathy
Progressive and proliferative synovial erosive changes failing to respond to medical management
May be associated with chronic posterior tibial tendinopathy and progressive valgus hindfoot deformity, eventual valgus tilt to the talus within the ankle mortise, potential lateral malleolar stress fracture, and compensatory forefoot varus
PATIENT HISTORY AND PHYSICAL FINDINGS
Patient history
Often a history of ankle trauma
Ankle fracture, particularly intra-articular
Ankle fracture with malunion
Chronic ankle instability (recurrent ankle sprains)
Chronic anterior ankle pain, primarily with activity and weight bearing
Ankle stiffness, particularly with dorsiflexion
Ankle swelling
Progressively increased pain with activity
Physical findings
Limp
Patient externally rotates hip to externally rotate ankle to avoid painful push-off.
Painful and limited ankle range of motion (ROM), particularly limited dorsiflexion
Mild ankle edema
Potential associated foot deformity
Post-traumatic arthrosis secondary to chronic instability may be associated with varus ankle and hindfoot and compensatory forefoot varus.
Inflammatory arthritis may be associated with progressively worsening flatfoot deformity, valgus tilt to the ankle and hindfoot, and equinus.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Weight-bearing AP with contralateral ankle included, lateral, and mortise views of the ankle
Weight-bearing AP with contralateral foot included, lateral, and oblique views of the foot, particularly with associated foot deformity
With associated or suspected lower leg deformity, we routinely obtain weight-bearing AP and lateral tibia–fibula views.
With deformity in the lower extremity, we occasionally obtain weight-bearing mechanical axis (hip-to-ankle) views of both extremities.
We occasionally evaluate complex or ill-defined ankle–hindfoot patterns of arthritis with or without deformity using CT of the ankle and hindfoot.
If we suspect avascular necrosis of the talus or distal tibia, we obtain an MRI of the ankle.
DIFFERENTIAL DIAGNOSIS
See the “Pathogenesis” section.
NONOPERATIVE MANAGEMENT
Activity modification
Bracing
Ankle–foot orthosis
Double upright brace attached to shoe
Stiffer-soled shoe with a rocker-bottom modification
Nonsteroidal anti-inflammatories or COX-2 inhibitors
Medications for systemic inflammatory arthropathy
Corticosteroid injection
Viscosupplementation
SURGICAL MANAGEMENT
In contrast to essentially all other total ankle systems, the INBONE™ total ankle system uses intramedullary rather than extramedullary referencing.
While the intramedullary alignment guide passes through the plantar foot, calcaneus talus, and tibia, it does so anterior to the posterior facet of the calcaneus and does not violate any articulations of the subtalar joint.
To achieve reliable intramedullary alignment, the INBONE™ total ankle system uses a leg frame that is initially cumbersome, demands more pre-incision preparation, and requires greater fluoroscopy time than other total ankle systems. However, with experience this technique becomes manageable and allows the user to correct deformities prior to making bone cut.
In our opinion, the INBONE™ total ankle system is perhaps more stout than some other systems.
We have been able to correct coronal and sagittal plane deformities through the tibiotalar joint with appropriate soft tissue balancing and corrective osteotomies relying also on the durability of the implants, particularly the broad talar component and the tibial stem extensions to maintain correction.
Preoperative Planning
The surgeon must be sure the patient has satisfactory perfusion to support healing and is not neuropathic.
Noninvasive vascular studies and potential vascular surgery consultation if necessary
The surgeon must inspect the ankle for prior scars or surgical approaches that need to be considered in planning the surgical approach for total ankle arthroplasty.
The surgeon must understand the clinical and radiographic alignment of the lower extremity, ankle, and foot.
The surgeon must be prepared to balance and realign the ankle. Occasionally, this necessitates corrective osteotomies of the distal tibia or foot, hindfoot arthrodesis, ligament releases or stabilization, and tendon transfers.
The surgeon should determine whether coronal plane alignment is passively correctable; this provides some understanding as to whether ligament releases will be required.
Ankle ROM is determined.
Ankle stiffness, particularly lack of dorsiflexion, needs to be corrected.
Anterior tibiotalar exostectomy
Posterior capsular release
Occasionally, tendo Achilles lengthening
Instrumentation
These instruments facilitate total ankle arthroplasty:
Small oscillating and reciprocating saws for fine cuts as well as larger oscillating saw for broad bone cuts. The smaller saws make it easier to resect prominences with precision, and easily morselize large bone fragments to be evacuated from the joint.
A rasp for final preparation of cut bony surfaces
A 90-degree angled curette, particularly to separate bone from the posterior capsule
A toothed lamina spreader to distract the joint and aid in realignment of preoperative ankle deformity. Since the INBONE™ prosthesis uses a monoblock cutting guide for tibial and talar resection, an intra-articular lamina spreader assists in limiting bone resection. A lamina spreader placed on the concave side of the joint also assists in realignment.
A toothless lamina spreader to judiciously distract the ankle to improve exposure even after preparing the surfaces of the tibia and talus
Large fluoroscopic scanner
Fluoroscopy confirms proper alignment of the cutting guide to the ankle.
The leg holder maintains the leg in position relative to the alignment guides and reference drill.
With the leg holder, the large scanner is necessary to straddle the leg and leg holder.
Fluoroscopy through the operating table is necessary, so a little fluoroscopy unit is inadequate.
Foot pedals to make adjustments to the table position
With the foot secured in the leg holder, subtle adjustments to the table's rotation confirm ideal alignment relative to the alignment guides.
Subtle adjustments to the alignment guides relative to the ankle allow fine-tuning for the reference drill trajectory.
Positioning
Supine
Plantar aspect of operated foot at end of operating table
Foot and ankle well balanced with toes directed to the ceiling
A bolster under the ipsilateral hip prevents undesired external rotation of the hip.
We routinely use a thigh tourniquet and regional anesthesia.
A popliteal block provides adequate pain relief postoperatively, particularly if a regional catheter is used. Moreover, hip and knee flexion–extension is not forfeited, facilitating safe immediate postoperative mobilization.
However, using a thigh tourniquet with a popliteal block typically requires a supplemental femoral nerve block (patient temporarily forfeits knee extension in the immediate postoperative period) or general anesthesia.
The operative extremity needs adequate space for the INBONE™ leg holder. The surgeon should be sure the opposite extremity is not secured too close to the operative extremity.
Approach
Anterior approach to the ankle, using the interval between the tibialis anterior (TA) tendon and the extensor hallucis longus (EHL) tendon
TECHNIQUES
APPROACH
Make a longitudinal midline incision over the anterior ankle, starting about 10 cm proximal to the tibiotalar joint and 1 cm lateral to the tibial crest.
Continue the incision midline over the anterior ankle just distal to the talonavicular joint.
At no point should direct tension be placed on the skin margins; we perform deep, full-thickness retraction as soon as possible to limit the risk of skin complications.
Identify and protect the superficial peroneal nerve by retracting it laterally.
In our experience there is a consistent branch of the superficial peroneal nerve that crosses directly over or immediately proximal to the tibiotalar joint.
We then expose the extensor retinaculum, identify the course of the EHL tendon, and sharply but carefully divide the retinaculum directly over the EHL tendon.
We always attempt to maintain the TA tendon in its dedicated sheath if present.
Preserving the retinaculum over the TA tendon prevents bowstringing of the tendon and thereby reduces the stress on the anterior wound. Should there be a wound dehiscence, then the TA is not directly exposed.
However, preserving the retinaculum over the TA tendon is not always possible. Not infrequently only the retinaculum is present over the tendon and it will be free with the EHL tendon (TECH FIG 1).
Use the interval between the TA and EHL tendons, with the TA and EHL tendons retracted medially and laterally, respectively.
Identify the deep neurovascular bundle (anterior tibial–dorsalis pedis artery and deep peroneal nerve) and carefully retract it laterally throughout the remainder of the procedure.
Perform an anterior capsulotomy and elevate the tibial and dorsal talar periosteum to about 6 to 8 cm proximal to the tibial plafond and talonavicular joint, respectively.
Elevate this separated capsule and periosteum medially and laterally to expose the ankle, access the medial and lateral gutters, and visualize the medial and lateral malleoli.
Remove anterior tibial and talar osteophytes to facilitate exposure and avoid interference with the instrumentation.
TECH FIG 1 • In this case there is no separate sheath for the tibialis anterior (TA) tendon. Nonetheless, the retinaculum was opened lateral to the tendon, and upon closure the TA will not be immediately up against the suture line.
TIBIOTALAR ALIGNMENT
Before placing the lower leg in the INBONE™ foot and ankle holder, we optimize ankle soft tissue balance and alignment.
Varus malalignment
We routinely perform a comprehensive medial release for moderate to severe varus malalignment.
The concept is similar to balancing the varus knee for total knee arthroplasty and was well described by Bonnin et al.1 in their 2004 report of the Salto prosthesis.
We routinely subperiosteally raise a continuous soft tissue sleeve from the distal medial tibia to the medial talus.
There is no need to be aggressive on the medial talus, as this could compromise the deltoid branch of the posterior tibial artery that perfuses the medial talar dome.
The superficial deltoid (medial collateral) ligament is elevated but left intact proximally and attached distally. The release of these fibers is complete when the posterior tibial tendon can be visualized.
The deep deltoid (medial collateral) ligament may be peeled off the medial malleolus to balance the ankle appropriately. In severe varus deformity, the entire deep deltoid ligament must be released to achieve tibiotalar balance (TECH FIG 2A). Overrelease is theoretically possible, but in our experience, with severe varus deformity, the ankle will not collapse into valgus even with a complete release.
In our experience, with an appropriate medial release, optimal bony resection and metal component alignment, and proper sizing of the polyethylene, a lateral ligament reconstruction is seldom necessary. One exception is when there has been an avulsion fracture of the tip of the fibula: in that instance it is difficult to obtain any ability to rotate the ankle against the lateral tissue, and a Brostrom ligament reconstruction can be done at the beginning of the case (TECH FIG 2B–D). This marks a significant change from our initial practices in rebalancing the varus ankle.
A lamina spreader placed in the medial tibiotalar joint maintains the correction.
Valgus malalignment
Likewise, a valgus malalignment must be rebalanced.
However, in our experience, we rarely need to perform a ligament release.
Often, valgus malalignment is secondary to lateral ankle joint collapse and some medial (deltoid) ligament attenuation. This may involve a component of lateral ankle ligament instability as well.
While the latter portion of this statement seems counterintuitive, it has been our experience in treating many patients with end-stage ankle arthritis and valgus malalignment.
Moreover, lateral release in such situations may lead to paradoxical lateral instability!
We use a lateral lamina spreader to realign the ankle and regain functional tension in the medial ligaments (TECH FIG 2E,F).
TECH FIG 2 • A. In this varus ankle a complete medial peel of the deltoid ligament has been performed and the ankle can be opened up with the lamina spreader. B. There was a large ossicle at the tip of the fibula representing an old avulsion fracture containing the anterior talofibular ligament. Hence, the bone was removed (C) and a Brostrom ligament reconstruction was performed (D). E. Valgus ankle with AP alignment guide properly rotated. However, the talus is not orthogonal to the guide or the tibia. F. In this view the lamina spreader has been placed laterally on the concave side, and now the talus is orthogonal to the tibia and the alignment guide.
INTRAMEDULLARY ALIGNMENT
Be sure the foot and ankle frame is properly assembled and the alignment drill guide trajectory is calibrated. If unsure, you can assemble the cannula into the holder, put the drill in, and take a fluoroscopic view to make sure they coincide (TECH FIG 3A).
The foot and lower leg are secured in the leg holder.
With correction of the preoperative deformity, we transfer the leg into the foot and ankle holder with the lamina spreader in place (TECH FIG 3B).
If the foot and ankle are secured first, it may be difficult to position the lamina spreader effectively.
Proper rotation
We use a small straight osteotome in the medial gutter as a reference. The foot is rotated until the osteotome is parallel with the leg holder foot plate.
Plantigrade foot
The heel must be flush with the foot plate of the guide.
If it is not, then the talar cut will have a posterior slope, removing an excessive amount of the talar body and increasing the risk of posterior talar component subsidence. Be sure all anterior tibiotalar osteophytes are removed. Perform a gastrocnemius release or tendo Achilles lengthening if necessary.
Coronal plane alignment
In the mediolateral plane, center the heel over the starting point for the reference drill.
We use the AP alignment guides to grossly set this alignment.
This position should also be in line with the tibial shaft axis so that minimal adjustments will be necessary.
Preoperative deformity complicates such preliminary alignment.
Sagittal plane alignment
We use the lateral alignment guides to grossly set this alignment.
The calf and Achilles rests need to be adjusted to optimize the lower leg's position relative to the foot (talus) (TECH FIG 3C).
In our experience, proper heel position, optimal tibial alignment, and ideal rotation may make the foot appear internally rotated relative to the lower leg.
Fluoroscopic confirmation of proper alignment
A large fluoroscopic scanner is needed (TECH FIG 3D,E).
TECH FIG 3 • A. Fluoroscopic view being obtained of leg holder with cannula and drill in place to ensure correct assembly of leg holder. B. Gelpi retractor holding deep tissue aside with lamina spreader on concave medial side of varus ankle. C. Leg positioned in leg holder with Achilles and calf rests supporting leg. D. C-arm coming in to obtain AP view of ankle on ipsilateral side. E. Overhead view of lamina spreader in place and deep Gelpi retractor holding deep tissue apart. C-arm to the left is coming in for lateral view. F. Foot pedals are used to control tilting of the table to get the alignment sites exactly parallel to one another.
Foot pedals to make adjustments to the table position (TECH FIG 3F)
With the foot secured in the leg holder, subtle adjustments to the table's rotation confirm ideal alignment relative to the alignment guides.
Subtle adjustments to the alignment guides relative to the ankle to allow fine-tuning for the reference drill trajectory may be made with the foot pedal.
Reference drill
Make a horizontally oriented 1-cm incision in the plantar foot, directly in the opening in the foot frame for passing the reference drill.
1 cm allows for subtle adjustments to the medial and lateral position of the reference drill, even when its drill sleeve has been positioned on the plantar calcaneus.
The incision should not be more than a 5 mm deep, since otherwise it could injure the lateral plantar nerve.
Insert the drill guide to contact the plantar calcaneus.
Avoid holding the frame while inserting this guide as this could allow the drill to bend, achieving a different trajectory than the guide.
Secure the drill guide.
Advance the reference drill from calcaneus to tibia.
Since the trajectory may change when the drill hits the plantar medial calcaneus, we typically start the drill in reverse and “peck drill” (tap drill) to gradually penetrate the plantar calcaneal cortex without veering from the planned trajectory.
Once the plantar cortex is penetrated, the drill is run in forward.
Since drilling may shift the frame slightly, fluoroscopic confirmation of proper alignment must be re-established, after which proper alignment of the reference drill may be confirmed.
Advance the drill into the distal tibia, about 8 to 10 cm.
Confirm appropriate reference drill position fluoroscopically in both the coronal and sagittal planes.
TIBIOTALAR JOINT PREPARATION
Sizing
Approximate sizing for the component may be performed on preoperative radiographs of either the involved side or the uninvolved opposite ankle.
Position the cutting block in roughly the correct position by using the reference drill guide to estimate its position.
Fine-tune the cutting block using the reference drill guide under fluoroscopy.
In the AP plane we align the cutting guide with the reference drill guide (TECH FIG 4A).
In the lateral plane, we use saw blades through the cutting guide to determine the resection level (TECH FIG 4B).
The position of the cutting block should be finalized only if proper alignment has been confirmed fluoroscopically with the alignment guides.
It is important that the guide is centered medially and laterally and no more than 1 mm of bone is removed form the medial malleolus.
Pinning the cutting block
Once proper position of the cutting block is established, the block is pinned, tibial pins first and talar pins next.
Occasionally the talar pins will skive and not engage the talus, particularly if a lamina spreader is being used to distract the joint or if the talar dome is sclerotic.
A toothless lamina spreader may be used to gently keep the talar pins in position as they are driven into the bone, but do this carefully because too much pressure may cause the pins to permanently bind in the cutting guide.
Two more pins are placed in the medial and lateral gutter.
Their mediolateral position is determined on the fluoroscopic image of the final cutting block position.
These pins protect the malleoli.
If a lamina spreader was used to distract the joint, it will interfere with the pin placement.
TECH FIG 4 • A. The cutting guide has been placed over the ankle and centered on the drill. B. A lateral view of the cutting guides with the saw and “dummy” blade in place gives the surgeon the amount of bone resected on the top of the talus and the bottom of the tibia.
Try to keep it in place long enough to get enough pins in so that when the lamina spreader is removed, the correction is maintained.
Withdraw the axial reference drill.
Anti-rotation drill
The anti-rotation drill corresponding to the cutting block is used to drill the anti-rotation slot in the tibia (the sagittal prominence on the tibial base plate).
Bone resection
With the soft tissues protected, make the tibial and talar cuts.
The bone resection should go all the way through the posterior cortex for each cut. It may not be possible on the initial pass, depending on the height of the cutting block and the particular saw used. After the initial cut, the cutting block can typically be lowered to complete the cuts, or the cuts can be freehand after the initial cuts. Obviously, avoid plunging the saw blade. Release the Achilles support to help prevent the flexor hallucis longus from being forced anteriorly and cut with the saw. Gently tapping the saw on the posterior cortex is usually possible to confirm that there is still cortex in place.
Once the posterior cortex has been penetrated for all cuts, the cutting guide and its pins can be removed.
The resected bone is evacuated from the joint.
A toothless lamina spreader may be used to facilitate accessing the most posterior bone.
Avoid levering on the malleoli with the instruments, as they may break.
A rongeur and an angled curette are ideal to remove the bone.
A fine reciprocating saw may be necessary to morselize the resected bone to facilitate removing all of the bone. Avoid cutting into the prepared tibial and talar surfaces with this saw, and protect the malleoli.
Tibial reaming
Secure the reamer tip to its shaft within the joint (TECH FIG 5). A toothless lamina spreader may be required to facilitate securing the reamer tip.
Advance the reamer. We typically use four segments for the stem extension; this requires reaming 55 mm into the tibia.
Extract the reamer tip from the joint. When the wrench is placed on the reamer tip, avoid activating the driver, as it will spin the reamer and the wrench, which then may fracture a malleolus. Keep your fingers off the trigger during this portion. With the wrench secured to the reamer tip and firmly held with one hand, set the driver for reverse and disengage the shaft from the tip, thereby protecting the malleoli. Extract the reamer tip from the joint and withdraw the reamer shaft from the plantar foot.
Talar preparation
Secure the talar alignment guide sleeve to the plantar aspect of the foot plate.
Advance the talar positioning guide through this sleeve to the prepared talar surface.
TECH FIG 5 • Reamer tip being assembled onto reamer to ream out distal tibia.
Secure the talar pin guide to the positioning guide and place the talar pin. Check to see if the pin will be appropriately placed in the prepared talar surface; if not, then the talar pin guide affords multiple options for pin positioning. Alternatively, the pin may be placed in the “0” position and then the talar pin guide may be used over that initial pin to position a second, more appropriately positioned pin.
We have also used the talar trial to determine optimal pin position. The talar trial may be positioned in the ideal mediolateral position and on the posterior cortex (TECH FIG 6A). The pin can then be placed through the talar trial and will then be in the ideal position. The talar trial is positioned on the talar pin and a lateral fluoroscopic view confirms that the talar component will be in the desired position.
Optimally, the talar pin (which is the drill guide for the talar stem) is just posterior midpoint to the center of the calcaneal posterior facet. In the radiograph shown in Techniques Figure 6B, the component and talar pin are too far posterior. The talar trial and pin were moved anteriorly before drilling the talar stem hole. The new correct position is seen on the intraoperative films at the end of the case (TECH FIG 6C).
This also determines which of the two stem sizes is to be used. The 10-mm stem can typically be attached to the talar component on the back table and the talar dome–stem combination may be inserted simultaneously. For the 14-mm stem, we typically place this stem first and then attach the talar dome separately.
Remove the talar trial and ream the talar stem guide pin to either 10 mm or 14 mm (TECH FIG 6D).
TECH FIG 6 • A. Talar component trial with hole and talar stem guide pin through it to determine position of stem. B. Cannulated drill being used over guide pin to create hole for stem. C. Lateral view of talar component with the talar stem guide through it. The guide and prosthesis are too far posterior and were brought forward. D. Final intraoperative lateral view showing that the prosthesis was moved forward and is in the correct position.
COMPONENT IMPLANTATION
Assemble the tibial stem within the joint.
We routinely leave the ankle plantarflexed, assemble the first two segments of the tibial stem on the back table, and insert them into the reamed tibia with the corresponding wrench (TECH FIG 7A).
Return the ankle to the neutral position in which the tibia was reamed and introduce the “X-screw driver” from the plantar foot while the next tibial stem segment is positioned within the joint using the corresponding clip (TECH FIG 7B). A toothless lamina spreader to gently distract the joint may be needed to introduce the next segment.
Using the X-screw driver and while securing the wrench holding the other two segments in the tibia, secure the third segment to the stem (TECH FIG 7C). Be sure to hold the wrench that is stabilizing the two segments already in the tibia; if the third segment is advanced and secured and then turned, the wrench could impact the malleolus and break it.
Remove the X-screw driver and place the rod impactor from the plantar foot to advance the three-segment stem into the tibia (TECH FIG 7D). Obtaining a radiograph at this point can help ensure the correct angle of placement in this varus ankle (TECH FIG 7E). Be sure to attach the appropriate wrench to the third segment while impacting the stem to avoid having the stem advance too far into the tibia.
TECH FIG 7 • A. The foot is plantarflexed to allow insertion of the cone piece with one mid-stem cylinder attached. B. Wrench holding already inserted pieces in place while another mid-stem component is being inserted. C. X-screw driver being inserted into stem component to screw it in place. D. Stem components inserted waiting for wrench to be attached before tapping stem up into tibia E. AP view of stem just before wrench is attached and stem is pushed up into tibia.
TECH FIG 8 • A. Base plate of tibial component being inserted onto base of stem. Note male Morse taper. B. Trimming away of bone using small reciprocating saw to ensure final fit. C. Base plate with stem being tapped up into tibia.
Repeat the steps to attach the fourth segment to the third segment. Add additional segments as needed. We typically use four segments.
The final segment is different from the others in that it houses the female portion of the Morse taper. It also has a small hole that indicates proper rotation. Be sure this segment is aligned and rotated properly. Then the entire stem is fully seated with its corresponding wrench using the rod impactor.
Tibial base plate
Introduce the tibial base plate into the joint (TECH FIG 8A).
Withdraw the rod impactor from the stem slightly, allowing the tibial base plate to be positioned, and then use the rod impactor to secure the base plate to the stem. The tibial base plate is secured to the stem by means of a Morse taper (TECH FIG 8A).
Once the Morse taper is secured, remove the wrench on the stem and the composite base plate and stem combination is ready to be fully seated. Make sure there is enough room for the base plate, and trim out any bone on the sides, which could lead to a malleolus fracture (TECH FIG 8B).
During this step, rotation of the tibial component must be controlled. A narrow handle attaches to the anterior aspect of the base plate to control rotation as the tibial component is impacted. When the component is fully seated it should rest snugly in the mortise (TECH FIG 8C).
Talar component
In our opinion, this is the most challenging step of the procedure, particularly if the joint was distracted to minimize bone resection or to correct deformity. In this situation, the joint space is quite tight by design, to achieve optimal soft tissue balance and ligament tension.
We routinely assemble a 10-mm stem to the talar dome component on the back table for the size 2 and 3 prosthesis, using the dedicated assembly device to secure the Morse taper.
Typically, a 14-mm stem is too long to be connected to the talar dome component before implantation. Therefore, we place the 14-mm talar stem first for size 4 and up if there is enough depth to the talus and seat it to the thin rib wrench that is flush with the prepared talar surface (TECH FIG 9). Since the Morse taper has not been secured, the rib wrench must remain under the 14-mm talar stem.
The joint must then be gently distracted with a lamina spreader, followed by insertion of the talar dome component. The toothless lamina spreader may need to go under the talar dome component to obtain the distraction, while the talar component is carefully forced posteriorly into position. A handle attached to the talar dome component facilitates driving the talar dome posteriorly. A protective plastic sleeve inserted onto the tibial base plate protects the talar dome from being scratched.
TECH FIG 9 • Fourteen-millimeter stem inserted first with rib wrench underneath and component impacted onto stem. Rib wrench prevents stem from being impacted before Morse tape is seated. Plastic trial protects talar dome surface.
TECH FIG 10 • Trial in place to determine final thickness of final polyethylene component.
Once the talar dome component seats on the stem, use the talar dome impactor to secure the Morse taper, with the rib wrench still between the talar dome component and the prepared talar surface.
Remove the rib wrench and inspect the interface between talar dome and stem to ensure that the two talar components are securely attached. Use the impactor to fully seat the talar component.
While impacting the talar component, use the handle that inserts into the talar dome to control subtle changes in rotation of the talar component.
Polyethylene insertion
The polyethylene trials determine optimal polyethylene thickness (TECH FIG 10).
We routinely remove the leg from the leg holder and obtain AP and lateral fluoroscopic images at this stage to confirm proper position and balance of the components.
With the ankle in neutral position, there should be a balance with varus and valgus stress. If not, the polyethylene thickness may be inappropriate or, more likely, balance needs to be established. Typically, the medial joint (deltoid ligament) is too tight. Traditionally, we have performed a lateral ligament reconstruction (modified Brostrom or BrostromEvans); however, in our more recent experience, we have been successful in rebalancing the ankle with a deltoid ligament release (described above) and increasing the polyethylene thickness.
The ankle should dorsiflex to at least 5 degrees, preferably 10 degrees beyond neutral. If not, the polyethylene thickness may be too thick. If the polyethylene thickness is appropriate and the foot cannot be dorsiflexed to 90 degrees, consider a gastrocnemius recession or percutaneous tendo Achilles lengthening.
Using the dedicated polyethylene insertion device, insert the polyethylene (TECH FIG 11A). In our experience, the polyethylene will engage the tibial base plate's locking mechanism most effectively with the following maneuvers:
Have an assistant or co-surgeon distract the joint.
During the initial portion of the insertion, gently pull the insertion device into slight plantarflexion, thus driving the polyethylene into the tibial base plate's locking mechanism.
Once the polyethylene has cleared the superior dome of the talar component, ease off on the plantarflexion of the insertion device and have the assistant or co-surgeon compress the joint, thereby forcing the polyethylene into the locking mechanism.
Remove the insertion device and fully seat the polyethylene with the dedicated impactor. With that accomplished, the prosthesis should be fully seated (TECH FIG 11B).
Obtain final AP and lateral fluoroscopic views of the valgus ankle (TECH FIG 12).
TECH FIG 11 • A. Polyethylene insertion device that screws down and pushes polyethylene onto tibial component tracks. B. Final component in position.
TECH FIG 12 • A, B. Final AP and lateral films taken in the operating room showing correction of initial valgus deformity.
CLOSURE
Thoroughly irrigate the joint and implant with sterile saline.
Reapproximate the capsule. We routinely use a drain.
Release the tourniquet and obtain meticulous hemostasis.
Reapproximate the extensor retinaculum while protecting the deep and superficial peroneal nerves.
Irrigate the subcutaneous layer with sterile saline and then reapproximate it.
Reapproximate the skin to a tensionless closure.
Apply sterile dressings on the wounds, adequate padding, and a short-leg cast with the ankle in neutral position.
POSTOPERATIVE CARE
Overnight stay
Nasal oxygen while in hospital
Touch-down weight bearing on the cast is permitted, but elevation is encouraged as much as possible.
Follow up in 2 to 3 weeks for cast change and suture removal
The patient returns 6 weeks after surgery for cast removal and weight-bearing radiographs of the ankle.
OUTCOMES
While some recently reported outcomes are based on highlevel evidence, results of total ankle arthroplasty are almost uniformly derived from level IV evidence.
Functional outcome using commonly used scoring systems for total ankle arthroplasty (AOFAS [Kofoed, Mazur] and NJOH [Buechel-Pappas]) suggest uniform improvement in all studies, with follow-up scores ranging from 70 to 90 points (maximum 100 points).
Patient satisfaction rates for total ankle arthroplasty exceed 90%, although follow-up data for patient satisfaction often do not exceed 5 years.
Overall survivorship analysis for currently available implants, designating removal of a metal component or conversion to arthrodesis as the endpoint, ranges from about 90% to 95% at 5 to 6 years and 80% to 92% at 10 to 12 years.
At the time of this writing there are no published results available for the INBONE™ total ankle arthroplasty.
COMPLICATIONS
Infection (superficial or deep)
Neuralgia (superficial or deep peroneal nerve; rarely tibial nerve)
Delayed wound healing
Wound dehiscence
Persistent pain despite optimal orthopaedic examination and radiographic appearance of implants
Osteolysis
Subsidence
Malleolar or distal tibial stress fracture
Implant fracture (including polyethylene)
REFERENCES
1. 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.
2. Gougoulias N, Khanna A, Maffulli N. How successful are current ankle replacements? A systematic review of the literature. Clin Orthop Relat Res 2010;468:199–208.
3. Haddad SL, Coetzee JC, Estok R, et al. Intermediate and long-term outcomes of total ankle arthroplasty and ankle arthrodesis: a systematic review of the literature. J Bone Joint Surg Am 2007;89A:1899–1905.