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Current And Emerging Insights On Total Ankle Replacement
Given the increasing popularity and evolution of total ankle replacements in recent decades, these authors discuss findings from the literature on current and emerging devices, and emphasize pertinent principles and pearls for success.
End-stage ankle arthritis can result in debilitating pathology that may lead to a painful, altered gait. Recent research has shown that ankle joint arthritis can lead to reduced quality of life similar to what physicians have found in patients suffering from hip arthritis.1-3
While the etiology of knee and hip arthritis is most commonly attributed to primary osteoarthritis (OA), arthritis of the ankle is more commonly associated with post-traumatic OA.4-7 Valderrabano and colleagues found that post-traumatic OA of the ankle was present in 78 percent of the patients they reviewed with end-stage tibiotalar arthritis.5 High- or low-energy ankle fractures, talus fractures, ankle dislocations or chronic ligamentous instability secondary to multiple prior sprains can lead to significant articular damage of the ankle, precipitating the arthritic decline.4 In addition to post-traumatic changes and chronic instability, systemic inflammatory arthropathy can also result in advanced arthritic change to the ankle.
While a tibiotalar arthrodesis is traditionally the gold standard, evolving techniques and improved implants have made total ankle replacement (TAR) a viable option with increasing utilization.1,3,6,8-10
New data has shown a surge in TAR implantation over the last two decades with good reported outcomes.1,3,11
Beginning in the early 1900s and initially becoming popular in the 1970s, total ankle implantation has had a steep evolutionary process with more regulated and reproducible design.12-14 The older or first-generation products mainly consisted of a two-component design varying from a “constrained” to an “unconstrained” implant with the distal tibia or talus consisting of the polyethylene component without a separate bearing.12-15
These early designs included a variety of implants.12–14 The St. Georg-Buchholz ankle prosthesis was a semi-constrained prosthesis inserted through a lateral approach. The Imperial College of London Hospital prosthesis was a two-component, constrained, cemented implant. The Irvine Ankle TAR (Howmedica) was unique in its talar anatomy design that highlighted the important attributes of the talus in TAR. The Richard Smith TAR was non-constrained. The Mayo TAR was a two-component design. These designs ultimately fell out of favor with poor survivorship due to increased wear resistance, stress deformation and significant bone loss.16
The progression of total ankle implant technology led to newer second- and third-generation design with the use of ultra-high molecular weight polyethylene (UHMWPE) while the most current designs are now considered fourth-generation prostheses. We can categorize these designs by their number of components (two versus three) and device type (fixed- versus mobile-bearing). The two-component system (fixed-bearing without a mobile piece) has the UHMWPE spacer retained within the tibial component of the implant. A three-component system (mobile-bearing with a mobile spacer) allows for independent mobility of the spacer as it articulates with the tibia and talar components.
The second-generation implants, including the Agility Total Ankle Replacement System (DePuy Synthes Orthopaedics), the Buechel–Pappas and the Scandinavian Total Ankle Replacement (STAR, Stryker Orthopaedics), were an improvement upon traditional ankle replacement. The Agility was unique in that it required a syndesmotic fusion as part of its approved technique. Despite some initial success, it is no longer commercially available and largely considered obsolete. With the new product lines available, we will not address the Agility implant in this article.12,17 The Buechel-Pappas implant is not in use in the United States.
The STAR implant, which is still in use today, is the only mobile-bearing implant approved by the Food and Drug Administration (FDA) for the U.S. market.12,14,17 The most recently developed TAR prostheses (i.e. third- and fourth-generation) have continued to improve upon old designs and have utilized new technology, including a patient-specific cut guide, improved UHMWPE wear, new insertional approaches, and overall improved survivorship.
With this in mind, let us take a closer look at the current TAR systems surgeons are using in the U.S. for ankle arthroplasty. The available implant systems include the aforementioned STAR device, Cadence Total Ankle System (Integra LifeSciences), Infinity Total Ankle System, Inbone II Total Ankle System and Invision Total Ankle Revision System (Wright Medical Technologies), Salto Talaris Total Ankle Prosthesis and Salto Talaris XT (Integra LifeSciences), Zimmer Trabecular Metal Total Ankle (Zimmer Biomet), and the Vantage Total Ankle (Exactech).
A Review Of Currently Available Total Ankle Implants
The STAR is an original second-generation (with multiple updates), unconstrained, mobile bearing total ankle implant developed in 1978 by Kofoed.14,15,18 It was originally a two-component, cemented system but was later modified to a three-component design with the addition of the polyethylene “mobile” spacer. It is currently the only mobile-bearing, cementless system approved for use in the U.S. The mobile component allows for rotation translation and can reduce the stress at the junction of the implant and bone interface.12 The STAR is one of the most implanted total ankle systems on the market with over 30 years of use (beginning in Europe) and 30,000 units sold.19
The STAR implant has a double barrel tibial interface with a chamfer-cut talus and a central sagittal ridge that interacts to the polyethylene spacer. It remains one of the most well studied systems and has demonstrated good functional success, including 80 to 90 percent survivorship at 10 years and 95.4 percent survivorship at 12 years without cement use in some studies.6,18-22 However, alternate recent reports have shown a decreased 10-year survival rate (70.7 percent) and deteriorating survivorship at 14 years (45.6 to 47 percent).23,24 Authors have noted some of these discrepancies in prior systematic reviews for the STAR implant, acknowledging that one may potentially encounter inventor or consultant surgeon bias in the published data.25
The next set of TAR implants on the market include the Inbone II, Infinity Total Ankle System/Prophecy Preoperative Navigation Guide (Wright Medical Technologies) and Invision. These implants are two-component, fixed-bearing systems intended for primary and now revision (Invision) total ankle replacement. Initially, the Inbone I (third-generation) involved a saddle talar design. The FDA cleared the Inbone I in 2005 and it evolved into the Inbone II. While maintaining the intramedullary stemmed design and external jig application system, the Inbone II system had an upgrade to a sulcus talar design, increased anterior peg talar component fixation, and more durable polyethylene spacers.26,27 Adams and colleagues published early- to mid-term results of the Inbone I system with improvement in functional patient-reported outcomes and 89 percent implant survivorship at a 3.7-year follow-up.28 Recently, Harston and coworkers found good intermediate survival rates of 90.3 percent in their cohort of 151 patients (Inbone I) with 49 patients needing revision surgery due to impingement, infection and component loosening.29
The Infinity system (fourth-generation) is also a two-component, fixed bearing device but it does not use the intramedullary stems or require a large external jig for application. The Prophecy (using Infinity design components) TAR is a computed tomography (CT)-guided specific system, which creates cut guides for each patient’s unique anatomical profile. One can use the Prophecy with either Inbone II or Infinity. The results are accurate and the implant theoretically can reduce surgical times as the long leg jig and instrumentation are no longer necessary.30 The Infinity, without CT guidance, employs the use of the “extramedullary” guidance for alignment while keeping the same talar sulcus design that is in the Inbone II, allowing the surgeon the choice of either using the Inbone II or Infinity talus with an Infinity tibial tray.31
One recent study from Asaad and colleagues reported on the early results of the Infinity system in 35 patients with a one-year follow-up.32 Patients in the study had improved American Orthopaedic Foot and Ankle Society (AOFAS) and Visual Analogue Scale (VAS) scores with wound healing and intraoperative medial malleolar fractures among the reported complications. The Invision system is intended for revision total ankle arthroplasty with a larger tibial tray and anterior talar component extension to support the implant on good cortical bone.
The Salto Talaris Total Ankle Prosthesis is a third-generation implant originally designed in the mid-1990s as a mobile-bearing device (Salto Mobile) for utilization outside of the U.S. In 2006, the FDA cleared a fixed-bearing, two-component version of this implant, which became available for use within the U.S. This implant system has a central “keel” for tibial fixation, which violates the anterior tibia for insertion.33 One unique aspect of this system is that the designers focused on mimicking the anatomical articular surface of the talus by incorporating the curvature of the radius and biconvex surfaces.33 As a result, the tibia follows the talus with regard to axial rotational alignment.
Stewart and coworkers reviewed midterm qualitative data from 106 patients who had a Salto Talaris total ankle replacement with a minimum of a five-year follow-up.34 The authors reported improved VAS, AOFAS and Short Form-36 (SF-36) scoring, a 95.8 percent survival rate (at minimum five years) and a 19 percent reoperation rate overall. Recently, Gaudot and coworkers compared the mobile- and fixed-bearing versions of the prosthesis, noting a slightly short-term performance from the fixed-bearing implant but the results were not statistically significant.35
The Salto Talaris XT Revision Ankle Prosthesis is a fixed-bearing, semi-constrained system that one can use for both primary and revision total ankle cases. The tibial component has a short or long central “keel” to reduce bone loss and the UHMWPE spacer has more options for revision cases. The talar component is a flat-cut design but keeps the same conical tapered geometrical design as the primary implant.36,37
The Zimmer Trabecular Metal Total Ankle Replacement is a third-generation, two-component, fixed-bearing device that requires a transfibular approach for implantation. It is the only laterally based total ankle system in use in the U.S. This technique avoids the typical anterior-based incision over the ankle joint in an attempt to avoid wound healing issues reported with that approach.
The Zimmer implant uses a trabecular metal interface for both the tibial and talar inserts, and implantation is assisted via an external jig for medullary axis alignment. Instead of a standard flat cut tibia, the tibial component follows the natural anterior to posterior curve of the distal articular surface while the talar component has a medial to laterally based radius of curvature to allow axial motion.38 This system uses a highly cross-linked polyethylene spacer (HXLPE) that may have decreased wear and less debris in comparison to standard spacers.39 In one short-term follow-up study, Barg and colleagues reported a 93 percent survivorship at 36 months with no delayed union or nonunion of the fibula in 54 patients.40
The next two systems, the Cadence and Vantage Total Ankle, are newer to the total ankle market. The Cadence is a fourth-generation, two-component, fixed-bearing implant that the FDA cleared in 2016 with minimal tibial and talar resection. This system has a fibular recess within the tibia component to reduce contact and frictional force against the fibula. In addition, the HXLPE spacer is made in two “biased” forms (anterior and posterior) to offset anterior or posterior subluxation.41 The Vantage Total Ankle is a new TAR system that garnered FDA clearance in 2016. The system offers detailed tibial and talar anatomically-shaped implants with a unique cage peg to allow for bony ingrowth. This comes in both two- and three-component designs, but is available in the U.S. as a fixed-bearing device with a spacer “clipped” into the tibial tray.
Ensuring Proper Patient Selection For TAR
Proper patient selection is paramount to a successful outcome in elective total ankle replacement. Perform a full history and physical to determine if the patient had any previous surgeries, including the presence of retained hardware, previous infection, the presence or family history of neuropathy or vascular disease. Patients should discontinue all tobacco use prior to intervention to reduce wound complications and optimize osseous healing potential. One should attempt all non-operative treatments—including injections, physical therapy and bracing—prior to a surgical approach.
Total ankle replacement is indicated for primary, post-traumatic and inflammatory arthropathies as an alternative procedure to tibiotalar arthrodesis. Total ankle replacement offers improved mechanics and range of motion (ROM) in comparison to fusion with equivalent pain relief.3,8 Generally, the ideal candidate for TAR has a lower body mass index (BMI), adequate bone stock for implantation, limited or correctable angular deformity, a stable hindfoot, and is middle-aged or elderly.
Contraindications to TAR include the presence of neuropathy, active infection, severe peripheral arterial disease, inadequate bone stock and severe uncorrectable coronal plane deformity.15 Consider patients on a case-by-case basis if they have a history of ligamentous laxity and soft tissue compromise from previous surgeries (severe scarring, flaps or prolonged wound healing). Prolonged immunosuppression may be a relative contraindication due to the increased risk of wound complications and potential failure of the implant incorporation. Patients with high physical activity demands, including laborers, also should have extensive counseling regarding the risks of TAR in their given work situation and may not be ideal for TAR. Some surgeons are expanding their focus to include more active and younger patients, especially since post-traumatic ankle arthritis is often present in the third, fourth, and fifth decades of life.42
Key Pearls On Preoperative Planning
Patients may require a staged approach or the use of the adjunctive procedures to achieve a good outcome.43 Many surgeons prefer to balance the foot and ankle prior to TAR if significant deformity or instability is present. Address optimal soft tissue and osseous balancing to reduce stress across the implant, and reduce potential for implant failure. Imaging is essential for preoperative assessment and staging for eligible patients undergoing TAR. Obtain a full set of plain film radiographs, including hindfoot alignment, stress dorsiflexion and stress plantarflexion views as well as standard weightbearing foot and ankle views. Along with physical exam findings, one can base the decision for staging on adjacent arthritis, deformity and instability.
Computed tomography scans can be useful for mapping and potentially revealing a subchondral cystic formation, or other non-obvious defects present on plain films. This advanced imaging can evaluate adjacent joint arthritis that one may need to address intraoperatively or as part of a staged approach, and also help triangulate the location of retained or broken hardware. The Prophecy system utilizes a series of CT scans for preoperative planning to construct patient-specific cutting guides to potentially reduce surgical time and allows for preoperative review of the surgical plan. Additionally, magnetic resonance imaging (MRI) may be beneficial for the assessment of talar or tibial cystic changes, the evaluation of soft tissue structures, and assessment for potential avascular necrosis-type changes of the talus. One potential downside to MRI in the presence of retained hardware is the creation of imaging artifact and distortion, making a CT a better modality for the evaluation of certain osseous pathology.
Consider electromyography (EMG) and nerve conduction velocity (NCV) testing in patients with reported subjective neuropathy and a correlating history. There should be a low threshold to evaluate for neuropathy as this would contraindicate the implantation of a total ankle prosthesis. Non-invasive vascular testing is important for patients with known comorbidities, including diabetes and a history of smoking. Patients with diabetes and tobacco users have known soft tissue and bone healing delays, both of which can be detrimental in the setting of a prosthetic joint.
How To Handle Intraoperative Complication Management
Intraoperative complications can occur at any level of surgery so surgeons must address and manage these appropriately. Fracturing of the medial and lateral malleolar is a known intraoperative complication that one can prevent by placing prophylactic screws prior to the procedure. Surgeons can protect the lateral malleolus with an axially placed full-threaded screw and strengthen the medial malleolus with the placement of a fully threaded screw in the standard fashion for an open reduction internal fixation. Alternately, surgeons can place provisional wires and, if necessary, advance screws over the wires.
Surgeons can minimize the risk of malleolar fracture by maintaining proper positional alignment and component sizing. Management of deformity simultaneous to the TAR procedure is beyond the scope of this article but typically includes a series of soft tissue releases or advancements, sometimes supplemented with osteotomies or tendon transfers. Take care not to “overstuff” the joint by simply increasing the size of the UHMWPE spacer in cases of residual deformity and limited range of motion as this may lead to predictably poor results.
Pertinent Principles For Successful TAR Procedures
• On approach, employ meticulous dissection without violation of the tibialis anterior tendon sheath to reduce edema and soft tissue healing complications.
• Consider limited use of retraction until you have performed the ankle arthrotomy and blunt dissection of the distal tibia and talus can support deep retraction.
• Tagging the extensor retinaculum on the approach for later repair may help with closure.
• Removing the tibial bone block in one piece can reduce operative time and bony fragmentation within the implantation site. Large bone pieces can get lodged posteriorly and cause posterior ankle impingement and residual pain.
• Segmenting the tibial component is sometimes necessary and one should take care to remove all fragments.
• The surgeon may want to consider having a low threshold for malleolar fixation if a stress response or occult fracture is evident intraoperatively.
• Since the so-called “learning curve” resets with each new prosthesis, ensure sound competency with any device you intend to use and train appropriately through multiple cadaver labs and technique reviews.
• Consider staging the ankle for a replacement in patients with multiplanar deformities (i.e. pes plano valgus, cavus).
• We cannot overstate the importance of proper procedure and patient selection for this surgery.
• Understanding the need for adjunctive procedures, including tendo-Achilles lengthening, lateral or medial ligament reconstruction, or bone grafting of cystic changes, is crucial to overall success.
Dr. Brandão is a Foot and Ankle Fellow at the Orthopedic Foot and Ankle Center in Westerville, Ohio.
Dr. Prissel is an attending physician at the Orthopedic Foot and Ankle Center in Westerville, Ohio.
Dr. Hyer is the Co-Director of the Orthopedic Foot and Ankle Center Fellowship at the Orthopedic Foot and Ankle Center in Westerville, Ohio.
References
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Editor’s note: For related articles, see “A Closer Look At Total Ankle Replacement Revision” in the February 2014 issue of Podiatry Today, “Study Focuses On TAR Survivorship After Subtalar Joint Arthrodesis” in the February 2017 issue or “Study Finds Good Patient Satisfaction Two Years After TAR Procedure” in the October 2017 issue.
