Operative Techniques in Orthopaedic Surgery (4 Volume Set) 1st Edition

479. TNK Total Ankle Arthroplasty

Yasuhito Tanaka and Yoshinori Takakura

DEFINITION

images Total ankle arthroplasty (TAA) is indicated for end stage osteoarthritis or rheumatoid arthritis.2

images The semi-constrained TNK ankle is a two-component total ankle implant (FIG 1).10,11

images 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

images 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

images 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

images Occasionally, severe pes planovalgus deformity, particularly that associated with stage IV posterior tibial tendon insufficiency, may result in a valgus-type ankle OA.5

images In our experience, a varus-type ankle OA may develop, typically characterized by varus deformity of the tibial plafond.3,4

images Advanced rheumatoid arthritis (RA) affects the ankle in 25% of patients.8

images The talonavicular, subtalar, and calcaneocuboid joints are involved in 29%, 39%, and the calcaneocuboid joint in 25%, respectively.7

images

FIG 1  The TNK ankle is a semiconstrained artificial joint made of alumina ceramic.

NATURAL HISTORY

images 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.

images We routinely use Larsen's grading scheme for evaluating the stage of RA.

images TAA is indicated for Larsen's grades 3 and 4.

images In our opinion, grade 5 (mutilans-type of RA) is contraindication for TAA.

PATIENT HISTORY AND PHYSICAL FINDINGS

images Osteoarthritis

images 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.

images Rheumatoid arthritis

images Morning stiffness, symmetrical joint pain, and joint swelling in the hands, wrists, and feet are distinctive symptoms of RA.

images In our experience, the ankle is usually not involved until advanced stages of RA.

images Typically, patients complain of pain with ankle range of motion (ROM) and swelling.

images 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.

images 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

images 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.

images Generally, we select the largest possible component to optimize the biomechanical advantage of maximum surface contact between implant and bone.

images In complex cases, we utilize computer simulation to more accurately template the implants (FIG 2).

images Weight-bearing radiographs of the ipsilateral foot are important when ankle arthritis is associated with foot malalignment/deformity.

images

FIG 2  Preoperative computer simulation. A. AP view. B. Lateral view.

images We routinely evaluate the hindfoot in any patient being considered for TAA.

images Occasionally, computed tomography (CT) is necessary to provide greater detail of potential subtalar pathology (FIG 3).

images As for laboratory tests, anticyclic citrullinated peptide (CCP) antibodies and galactose deficient IgG are useful to an early diagnosis.

NONOPERATIVE MANAGEMENT

images Osteoarthritis

images Activity modification; bracing

images Some patients benefit from heat treatments and ultrasound.

images NSAIDs

images Judicious use of corticosteroid injections

images Viscosupplementation

images Rheumatoid arthritis

images Anti-inflammatory medications

images Systemic rheumatoid medical management through a rheumatologist

images Bracing

images Judicious use of corticosteroid injections

SURGICAL MANAGEMENT

images 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

images 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.

images

FIG 3  CT is helpful for detecting subtalar lesions.

images 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

images Three sizes of the TNK prosthesis are available: small, medium, and large (FIG 4).

images 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.

images 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

images Supine position

images Thigh tourniquet

images Bolster under the ipsilateral hip to prevent excessive external rotation of the operated extremity.

images

FIG 4  Small, medium, and large sizes of the TNK ankle.

TECHNIQUES

APPROACH

images  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.

images  The dorsalis pedis artery and the deep peroneal nerve are retracted to the lateral side.

images  An anterior ankle capsulotomy is performed.

images  In RA, a comprehensive synovectomy is performed, from the extensor tendon sheath(s) to the talonavicular joint.

TIBIAL PREPARATION

images  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).

images  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.

images  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).

images  Although we recommend 10 degrees of posterior slope, we caution that excessive posterior slope is detrimental.

images  To maintain support for the prosthesis we avoid violating the posterior tibial cortex.

images  The medial malleolar preparation is performed next.

images

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

images  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.

images  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.

images  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).

images  A spacer is now inserted to confirm adequate and balanced bone resection (TECH FIG 2C).

images  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).

images  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.

images  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).

images

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

images  The talar trial corresponding to the component size is impacted with a talar impactor.

images  The appropriately sized talar trial is positioned on the prepared talus and impacted.

images  The tibial peg cutting guide is positioned on the anterior distal tibia (TECH FIG 3A).

images The superior and medial aspects of the guide are aligned with the prepared tibial surface.

images 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).

images  The tibial anchor is prepared along the inner surface of the guide.

images We recommend preserving the posterior tibial cortex at the anchoring region mustbe left intact to prevent posterior tibial component migration (TECH FIG 3D).

images

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

images  The tibial trial is inserted

images  Proper alignment and satisfactory ankle ROM are confirmed (TECH FIG 4A).

images  Ideally, the tibial trial should be supported by both the anterior and posterior tibial cortices.

images  Once optimal alignment and ROM are confirmed, the trial components are removed

images  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).

images  With the ankle held in plantarflexion, the final talar component is impacted using the dedicated talar impactor.

images  Then, the tibial component is impacted with its specific impaction tool

images  Via the screw hole in the tibial component, a 2.5-mm drill is advanced through the posterior tibial cortex.

images 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).

images  Any residual gapping between the bone and tibialcomponent should be filled with cancellous bone autograft.

images  For patients with osteopenia, we routinely use bone cement for fixation of the components.

images

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

images  In patients with concomitant ankle and subtalar arthritis, we favor performing simultaneous TAA and subtalar arthrodesis (TECH FIG 5A,B).

images  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.

images  To facilitate fusion, a small diameter drill is used to penetrate the subchondral bone and increase the surface area of the subtalar joint.

images  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.

images

TECH FIG 5  Subtalar arthrodesis. A. Postoperative AP view with subtalar arthrodesis using a single OA cancellous screw. B. Lateral view.

CLOSURE

images  The wound(s) are thoroughly irrigated with sterile saline solution

images  We routinely use a drain.

images  The retinaculum and skin are reapproximated, taking care to protect the deep neurovascular bundle and superficial peroneal nerve.

images  A short leg cast is applied with the ankle in a neutral position.

images

POSTOPERATIVE CARE

images Patients with uncemented prostheses wear a cast for 3 weeks postoperatively, after which they gradually increase their active range of motion.

images 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.

images Patients with cemented prostheses wear a cast for 2 weeks, and full weight bearing is allowed after the cast is removed.

OUTCOMES

images From 1991 to 2001, we performed 70 TNK TAAs in 62 patients (FIG 5).10

images 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.

images Cemented TAA was performed in three ankles with OA and 19 ankles with RA (FIG 6).

images Revision surgery was performed for three ankles in three patients: two ankles with collapse of the talus, and one infected ankle.

images 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.

images

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.

images

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.

images 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.

images In the RA group, the same mean values improved from 14, 31, and 35 points to 35, 39, and 74 points, respectively.

images 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.

images 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.

images 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).

images 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).

images 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

images Intraoperative fracture of the medial malleolus

images Superficial peroneal nerve palsy

images Wound edge necrosis

images Superficial infection

images Deep infection

images Loosening of the implant

images Subsidence of the implant

REFERENCES

1. Buckwalter JA, Saltzman CL. Ankle osteoarthritis: distinctive characteristics. AAOS Instr Course Lect 1999;48:233–241.

2. Easley ME, Vertullo CJ, Urban WC, et al. Total ankle arthroplasty. J Am Acad Orthop Surg 2002;10:157–167.

3. Katsui T, Takakura Y, Kitada C, et al. Roentgenographic analysis for osteoarthrosis of the ankle. J Jpn Soc Surg Foot 1980;1:52–57.

4. Monji J. Roentgenological measurement of the shape of the osteoarthritic ankle. Nippon Seikeigeka Gakkai Zasshi 1980;54:791–802.

5. Pomeroy GC, Pike RH, Beals TC, et al. Acquired flatfoot in adults due to dysfunction of the posterior tibial tendon. J Bone Joint Surg Am 1999;81A:1173–1182.

6. Saltzman CL, Salamon ML, Blanchard GM, et al. Epidemiology of ankle arthritis: report of a consecutive series of 639 patients from a tertiary orthopaedic center. Iowa Orthop J 2005;25:44–46.

7. Seltzer SE, Weissman BN, Adams DF, et al. Computed tomography of the hindfoot with rheumatoid arthritis. Arthritis Rheum 1985;28:1234–1242.

8. Spiegel TM, Spiegel JS. Rheumatoid arthritis in the foot and ankle: diagnosis, pathology, and treatment: the relationship between foot and ankle deformity and disease duration in 50 patients. Foot Ankle 1982;2:318–324.

9. Takakura Y. The total ankle prosthesis: experimental and clinical studies. J Nara Med Assoc 1977;25:582–598.

10. Takakura Y, Tanaka Y, Sugimoto K, et al. Ankle arthroplasty: a comparative study of cemented metal and uncemented ceramic prostheses. Clin Orthop Relat Res 1990;252:209–216.

11. Takakura Y, Tanaka Y, Kumai T, et al. Ankle arthroplasty using three generations of metal and ceramic prostheses. Clin Orthop Relat Res 2004;424:130–136.



If you find an error or have any questions, please email us at admin@doctorlib.info. Thank you!