Yasuhito Tanaka and Yoshinori Takakura
DEFINITION
Total ankle arthroplasty (TAA) is indicated for end stage osteoarthritis or rheumatoid arthritis.2
The semi-constrained TNK ankle is a two-component total ankle implant (FIG 1).10,11
It is made of alumina ceramic, and its interface with bone is coated with alumina beads. This prosthesis combines biocompatibility of alumina ceramics with a design that facilitates fixation to bone.
ANATOMY
The physiologic alignment of the tibial plafond is nearly perpendicular to the anterior tibial shaft axis in the coronal plane and has a slight posterior slope relative to the lateral tibial longitudinal axis. To match this natural anatomy, the TNK ankle's tibial component is ideally implanted perpendicular to the anterior logitudinal axis of the tibia with a 10 degree posterior slope. The talar component is ideally set parallel to the ground or plantar aspect of the weight-bearing foot.
PATHOGENESIS
Ankle osteoarthritis (OA) is most commonly posttraumatic in origin, often secondary to intra-articular fractures with cartilage injury and/or malunions of the tibial plafond.1,6
Occasionally, severe pes planovalgus deformity, particularly that associated with stage IV posterior tibial tendon insufficiency, may result in a valgus-type ankle OA.5
In our experience, a varus-type ankle OA may develop, typically characterized by varus deformity of the tibial plafond.3,4
Advanced rheumatoid arthritis (RA) affects the ankle in 25% of patients.8
The talonavicular, subtalar, and calcaneocuboid joints are involved in 29%, 39%, and the calcaneocuboid joint in 25%, respectively.7
FIG 1 • The TNK ankle is a semiconstrained artificial joint made of alumina ceramic.
NATURAL HISTORY
Irrespective of cause, OA is characterized by a gradual, progressive, and diffuse loss of articular cartilage with eventual complete eburnation down to subchondral bone on both sides of the joint. RA originates from an inflammatory process of the joint's synovial tissue.
We routinely use Larsen's grading scheme for evaluating the stage of RA.
TAA is indicated for Larsen's grades 3 and 4.
In our opinion, grade 5 (mutilans-type of RA) is contraindication for TAA.
PATIENT HISTORY AND PHYSICAL FINDINGS
Osteoarthritis
Patients typically complain of ankle pain with weightbearing, particularly start of pain in the first few steps and also with prolonged walking. With progressive OA, pain with ankle motion and ankle edema become more common. Ankle stiffness is associated with advanced stages of OA.
Rheumatoid arthritis
Morning stiffness, symmetrical joint pain, and joint swelling in the hands, wrists, and feet are distinctive symptoms of RA.
In our experience, the ankle is usually not involved until advanced stages of RA.
Typically, patients complain of pain with ankle range of motion (ROM) and swelling.
Because RA may affect the talonavicular joint in isolation, ankle and talonvicular joint involvement must be distinguished. Careful examination of ankle and hindfoot palpation and stress usually allows differentiation between tibiotalar and talonavicular RA, but radiographic confirmation is often warranted.
Advanced RA of the ankle associated with pes planovalgus often has concommittent posterior tibial tendon tendinopathy and spring ligament pathology.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Weight-bearing AP and lateral radiographs of the ankle determine the extent of arthritis and deformity at the ankle. Preoperatively, we determine the appropriate implant size using dedicated template for the TNK system.
Generally, we select the largest possible component to optimize the biomechanical advantage of maximum surface contact between implant and bone.
In complex cases, we utilize computer simulation to more accurately template the implants (FIG 2).
Weight-bearing radiographs of the ipsilateral foot are important when ankle arthritis is associated with foot malalignment/deformity.
FIG 2 • Preoperative computer simulation. A. AP view. B. Lateral view.
We routinely evaluate the hindfoot in any patient being considered for TAA.
Occasionally, computed tomography (CT) is necessary to provide greater detail of potential subtalar pathology (FIG 3).
As for laboratory tests, anticyclic citrullinated peptide (CCP) antibodies and galactose deficient IgG are useful to an early diagnosis.
NONOPERATIVE MANAGEMENT
Osteoarthritis
Activity modification; bracing
Some patients benefit from heat treatments and ultrasound.
NSAIDs
Judicious use of corticosteroid injections
Viscosupplementation
Rheumatoid arthritis
Anti-inflammatory medications
Systemic rheumatoid medical management through a rheumatologist
Bracing
Judicious use of corticosteroid injections
SURGICAL MANAGEMENT
We favor TAA over tibiotalar arthrodesis for bilateral ankle arthritis and ankle arthritis associated with hindfoot stiffness/arthritis. In 1975, we developed a metal prototype of our TNK ankle.9
In 1980, because of improvements in materials and operative procedures, we developed a TNK ankle made of alumina ceramic.10 However, there were problems with the interface between bone and alumina ceramic, and the clinical results of the alumina ceramic TNK ankle were not satisfactory.
FIG 3 • CT is helpful for detecting subtalar lesions.
In 1991, we developed a bead-coated alumina ceramic TNK ankle11 and the current design has been modified from this version of the TNK implant.
Preoperative Planning
Three sizes of the TNK prosthesis are available: small, medium, and large (FIG 4).
We template for the TNK implant based on the preoperative weightbearing ankle radiographs, marking the proposed resection level. The planned resection line is 8 to 15 mm above the distal tibial surface, and has a 10 posterior slope.
The antero-posterior dimension of the tibia plafond is measured to ensure optimal support for the tibial implant. While we favor noncemented implants, we rarely consider cement fixation for patients with osteopenic bone or bone defects that do not allow full support for the prosthesis with standard tibial and/or talar resections. In an effort to limit initial micromotion of the implant and to promote effective bone ingrowth, we routinely secure the prosthesis to bone with screw fixation.
Positioning
Supine position
Thigh tourniquet
Bolster under the ipsilateral hip to prevent excessive external rotation of the operated extremity.
FIG 4 • Small, medium, and large sizes of the TNK ankle.
TECHNIQUES
APPROACH
A 10-cm longitudinal incision is centered over the anterior ankle. The extensor retinaculum is divided over the interval between the tibialis anterior and extensor hallucis longus tendons.
The dorsalis pedis artery and the deep peroneal nerve are retracted to the lateral side.
An anterior ankle capsulotomy is performed.
In RA, a comprehensive synovectomy is performed, from the extensor tendon sheath(s) to the talonavicular joint.
TIBIAL PREPARATION
Tibiotalar osteophytes are removed to expose the anterior joint. Based on preoperative templating and level of the tibial plafond, the tibial resection level is determined. The tibial cutting guide is positioned at the desired tibial resection level (TECH FIG 1A).
The external tibial alignment guide attached to the cutting block is oriented in line with the tibial shaft axis and the center of the patella.
Once properly oriented, the tibial cutting guide is secured to the tibia with a fixation pin and the distal tibial cut is performed with an oscillating saw advanced through the cutting block (TECH FIG 1B,C).
Although we recommend 10 degrees of posterior slope, we caution that excessive posterior slope is detrimental.
To maintain support for the prosthesis we avoid violating the posterior tibial cortex.
The medial malleolar preparation is performed next.
TECH FIG 1 • Osteotomy of the tibia. A. Tibial cutting guide and alignment bar. The alignment bar on the tibial cutting guide is adjusted to the center of the patella. B. Osteotomy is performed with 10 degrees of anterior opening. C. Osteotomy using a bone saw.
TALAR PREPARATION
The superior surface of the talar cutting guide is brought into contact with the resected distal tibia, with traction applied to the ankle in approximately 10 degrees of plantar flexion.
Proper alignment is confirmed using the external tibial alignment guide as was done prior to the tibial resection. The talar cutting is secured to the talus with a fixation pin.
Using an oscillating saw, the superior surface of the talar dome is prepared using the talar cutting guide as a reference (TECH FIG 2A,B).
A spacer is now inserted to confirm adequate and balanced bone resection (TECH FIG 2C).
The mediolateral talar cutting guide is properly oriented to the talus and secured. Using an oscillating saw through the capture slots of the cutting guide, 2 mm are removed from the medial and lateral talar dome (TECH FIG 2D,E).
Resection of more than 2 mm from either side of talus must be avoided by chosing the appropriate mediolateral cutting guide and orienting it properly; excessive resection may lead to talar component subsidence.
Next, the appropriately sized talar peg cutting guide (TECH FIG 2F) is positioned on the prepared talar surface, and the tibial peg hole is created (TECH FIG 2G).
TECH FIG 2 • Osteotomy of the talus. A. Talar cutting guide. B. Osteotomy is performed parallel to a floor line. C. To confirm the osteotomy of the tibia and talus, a spacer is inserted under traction. D. The talar margin cutting guide. E. The talar margin is cut in a plantarflexion position of the ankle. F. The talar peg cutting guide. G. The talar peg crusher.
PREPARATION OF THE TIBIAL ANCHOR
The talar trial corresponding to the component size is impacted with a talar impactor.
The appropriately sized talar trial is positioned on the prepared talus and impacted.
The tibial peg cutting guide is positioned on the anterior distal tibia (TECH FIG 3A).
The superior and medial aspects of the guide are aligned with the prepared tibial surface.
Once properly oriented with the prepared tibial surface and the talar trial, the tibial peg cutting guide is secured to the tibia (TECH FIG 3B,C).
The tibial anchor is prepared along the inner surface of the guide.
We recommend preserving the posterior tibial cortex at the anchoring region mustbe left intact to prevent posterior tibial component migration (TECH FIG 3D).
TECH FIG 3 • Osteotomy of tibial anchor region. A. The tibial peg cutting guide. B. The tibial peg cutting guide is inserted after placing the talar trial. C. Intraoperative view. D. Reaming is completed.
TRIAL AND SETTING
The tibial trial is inserted
Proper alignment and satisfactory ankle ROM are confirmed (TECH FIG 4A).
Ideally, the tibial trial should be supported by both the anterior and posterior tibial cortices.
Once optimal alignment and ROM are confirmed, the trial components are removed
We favor applying bone marrow aspirate from the patient's iliac crest to the bone ingrowth surfaces of noncemented implants to to accelerate early bone ingrowth. (TECH FIG 4B).
With the ankle held in plantarflexion, the final talar component is impacted using the dedicated talar impactor.
Then, the tibial component is impacted with its specific impaction tool
Via the screw hole in the tibial component, a 2.5-mm drill is advanced through the posterior tibial cortex.
A specially designed polyethylene sleeve is placed into the screw hole of the tibial component into which a 4.0-mm AO small fragment cancellous screw is inserted to secure the tibial component to the tibia (TECH FIG 4C,D).
Any residual gapping between the bone and tibialcomponent should be filled with cancellous bone autograft.
For patients with osteopenia, we routinely use bone cement for fixation of the components.
TECH FIG 4 • Trial and setting. A. The tibial trial is inserted. B. Bone marrow mounting. C. Screw fixation. D. Implantation is completed.
SUBTALAR ARTHRODESIS
In patients with concomitant ankle and subtalar arthritis, we favor performing simultaneous TAA and subtalar arthrodesis (TECH FIG 5A,B).
Through a 2.5-cm lateral incision over the sinus tarsi, the subtalar joint is exposed and residual articular cartilage is removed using a chisel and a curette.
To facilitate fusion, a small diameter drill is used to penetrate the subchondral bone and increase the surface area of the subtalar joint.
Through the anterior incision, anterior to the talar component, a standard AO cancellous screw is placed from the talar neck across the subtalar joint into the calcaneus.
TECH FIG 5 • Subtalar arthrodesis. A. Postoperative AP view with subtalar arthrodesis using a single OA cancellous screw. B. Lateral view.
CLOSURE
The wound(s) are thoroughly irrigated with sterile saline solution
We routinely use a drain.
The retinaculum and skin are reapproximated, taking care to protect the deep neurovascular bundle and superficial peroneal nerve.
A short leg cast is applied with the ankle in a neutral position.
POSTOPERATIVE CARE
Patients with uncemented prostheses wear a cast for 3 weeks postoperatively, after which they gradually increase their active range of motion.
During the first week, weight bearing is not allowed. In the following weeks, weight bearing to tolerance is permitted, with crutches. At 2 months postoperative, full weight bearing is initiated.
Patients with cemented prostheses wear a cast for 2 weeks, and full weight bearing is allowed after the cast is removed.
OUTCOMES
From 1991 to 2001, we performed 70 TNK TAAs in 62 patients (FIG 5).10
Follow-up was possible for 67 ankles in 60 patients: 39 ankles in 36 patients with OA (osteoarthritis group), and 28 ankles in 24 patients with RA (rheumatoid arthritis group). Duration of follow-up ranged from 24 months to 134 months, with an average of 62 months.
Cemented TAA was performed in three ankles with OA and 19 ankles with RA (FIG 6).
Revision surgery was performed for three ankles in three patients: two ankles with collapse of the talus, and one infected ankle.
Clinical evaluation was performed using our rating system,9 in which the maximum score of 100 points is divided into 40 points for pain and 60 points for function. Satisfactory pain relief was obtained in majority of patients.
FIG 5 • The TNK ankle replacement for osteoarthritis of the ankle (noncemented replacement). A. Preoperative AP view. B. Preoperative lateral view. C. Postoperative AP view at 8 years. D. Postoperative lateral view.
FIG 6 • The TNK ankle replacement for rheumatoid arthritis of the ankle (cemented replacement). A. Preoperative AP view. B. Preoperative lateral view. C. Postoperative AP view 2 years 6 months after the surgery. D. Postoperative lateral view.
In the OA group, mean values of pain, function and total score improved from 14, 34, and 48 points preoperatively to 37, 49, and 86 points at last follow-up, respectively.
In the RA group, the same mean values improved from 14, 31, and 35 points to 35, 39, and 74 points, respectively.
Preoperative and postoperative mean ankle ROM was 28 and 33 degrees in the OA group and 22 and 22 degrees in the RA group, respectively.
In the OA group, overall results were excellent in 24 ankles, good in 10 ankles, fair in 3 ankles, and poor in 2 ankles. In the RA group, overall results were excellent in 6 ankles, good in 12 ankles, fair in 7 ankles, and poor in 3 ankles.
In the RA group, mean total scores (using our own ankle rating system) at the follow-up were 77 points for cemented fixation (18 ankles) and 71 points for cementless fixation (10 ankles).
Radiography showed subsidence and loosening in four prostheses in the OA group (two tibial prostheses and two talar prostheses) and 17 prostheses in the RA group (six tibial prostheses and 11 talar prostheses).
Although the results of the RA group were worse than those of the OA group, shortand medium-term results with beadcoated alumina ceramic prostheses were encouraging.
COMPLICATIONS
Intraoperative fracture of the medial malleolus
Superficial peroneal nerve palsy
Wound edge necrosis
Superficial infection
Deep infection
Loosening of the implant
Subsidence of the implant
REFERENCES
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