Emerging Insights With The Ankle Implant Arthroplasty

Robert W. Mendicino, DPM, FACFAS, Alan R. Catanzariti, DPM, FACFAS, and Kyle S. Peterson, DPM

Can the total ankle replacement (TAR) provide a viable alternative to ankle arthrodesis? In addition to reviewing the FDA approved TARs in the United States, advances in device design and the current literature, these authors emphasize proper patient selection, sound pre-op planning and other insights from their experience in performing total ankle arthroplasty procedures.

End-stage osteoarthritis (OA) of the ankle is a major cause of pain and disability. The most common cause of ankle degeneration is previous trauma with ankle fracture-dislocations being common.1,2 The treatment for disabling ankle arthritis remains a controversial topic. Until recently, the “gold standard” treatment for painful arthritis has been an ankle arthrodesis.3-5 With unique designs, comprehensive patient follow-up and improved instrumentation, total ankle replacements (TARs) have become increasingly popular. These features now make the option of an ankle replacement more attractive.6

   Accordingly, let us take a closer look at the emergence of TAR, current literature and the evolution of TAR surgery at our institution.

   Lord and Marotte performed the first ankle prosthesis procedure in 1970.7 When only seven of 25 implants proved successful, they abandoned the procedure. Many design changes have occurred since the introduction of TAR in the early 1970s. Initially, the ankle prosthesis was highly constrained and consisted of a complete polyethylene tibial component, which required large bony resection and cement for implant fixation.8 Low patient satisfaction and a high complication rate — including loosening, subsidence and osteolysis — slowed the use and popularity of the prosthesis.9

   Newer implant designs, referred to as second- and third-generation implants, developed in the 1980s. They consisted of three pieces: tibial and talar metallic components, and a bearing surface made of high-molecular weight polyethylene interposed between the metallic components.8,10 These new generation implants are also classified as two- or three-component designs. The two-component implant, also referred to as a fixed-bearing device, locks the polyethylene piece within the tibial component. The three-component implant, referred to as a mobile-bearing device, provides two distinct and independent articulation interfaces for the polyethylene component, allowing translation, rotation and flexion.8

   The new implant designs were meant to function with less constraint, require less bone resection and utilize stems or pegs for fixation instead of cement.10 Many of the second-generation implants, though, had increased polyethylene wear and failure, leading to instability and even reported dislocation of the components.10 With the advent of the newest third-generation implants, manufacturers have placed more emphasis on improved instrumentation, soft tissue balance, a plantigrade foot and patient selection and education.11 These elements have led to greater long-term results.12,13

A Pertinent Review Of Approved Total Ankle Replacements

There are currently five total ankle replacement systems approved for use in the United States by the Food and Drug Administration (FDA). These devices include: the Agility LP Total Ankle System (DePuy); the INBONE total ankle (Wright Medical); the Salto Talaris anatomic ankle (Tornier); the Eclipse Total Ankle (Integra LifeSciences); and, most recently, the Scandinavian Total Ankle Replacement (STAR) (SBI). All the approved devices, except the STAR, are fixed-bearing, two-component systems. The STAR ankle is the only approved three-component, mobile-bearing system available for use in the U.S.

   Designed by Frank Alvine, MD, in 1984, the Agility LP Total Ankle Replacement is a two-component prosthesis, which was the first FDA-approved ankle replacement device in the U.S. The Agility device requires an arthrodesis of the distal tibiofibular syndesmosis to increase stability. It also requires the use of an external fixator in surgery to allow proper distraction. One would insert the tibial component in an externally rotated position of 22 degrees to mimic the natural transmalleolar axis. The Agility ankle is approved only with the use of bone cement. Long-term follow up from the creators of the implant have shown between a 90 to 93 percent satisfactory result.12,14

   The INBONE total ankle system was approved by the FDA in 2005. The system has a unique design, which is similar to that of a total knee replacement. One would implant the modular, multipiece tibial stem through an intramedullary reaming system. The talar component, also supported by a stem, has a surface of 1.5 to two times larger than other FDA-approved ankle devices.11

   Approved by the FDA in November of 2006, the Salto Talaris ankle device is a fixed-bearing ankle prosthesis. The U.S. implant is based off the original Salto prosthesis, a mobile-bearing three component system widely used in Europe. The improved two-component ankle system used in the U.S. utilizes a conical talar component with two different radii of curvature and a curved groove in the sagittal plane. The medial radius is smaller than the lateral to allow equal tensioning of the collateral ligaments. The tibial component is designed for a fixed insertion of the polyethylene bearing piece that is replaceable. The tibial component has a tapered plug on a pedestal, which one inserts through an anterior tibial cortical slot and drill hole in the bone.11

   The Eclipse total ankle garnered approval in November 2006. The surgeon inserts the implant through a medial or lateral approach rather than the typical anterior incision required by most TARs. Although this device is FDA-approved, only a few Eclipse total ankles have been implanted and this implant is not readily available to all surgeons.11

   Hakon Kofoed, MD, originally designed the STAR implant in 1978 as a two-component, cemented and unconstrained implant. This design was later modified in the 1980s to a cementless, mobile-bearing design. Arguably one of the most widely used ankle implants worldwide, the STAR just received FDA approval for use in the U.S. in May 2009. The STAR ankle is the only U.S. FDA-approved cementless and mobile-bearing, three-component system.

   The tibial component is designed for less bone resection and has two parallel bars for insertion into the subchondral bone. The talar component is meant to mimic the talar dome but has a central ridge for stabilization of the polyethylene piece. Both the tibial and talar components are sprayed with titanium plasma to aid in bony ingrowth.15 The first long-term study in the U.S. for the STAR, published in May 2011, reported an implant survival rate of 96 percent at five years and 90 percent at 10 years, which is in direct accordance with previous long-term research in Europe.13

Emphasizing Proper Patient Selection

Similar to any elective surgery, ensuring proper patient selection is key. One must obtain a thorough history and physical examination, and generally exhaust all methods of non-operative treatment. To date, there are no specific parameters to designate candidates for an ankle replacement. The literature does reveal, however, generalized characteristics of the ideal patient population. Patients typically present with: older age, low body mass, minimal osseous deformity and a lifestyle with a low physical demand.10

   Although these indications are generalized, absolute contraindications do exist. These contraindications include: peripheral neuropathy and/or Charcot neuroarthropathy; active infection; peripheral arterial disease; significant osseous malalignment or deformity (greater than 15 degrees varus/valgus); extensive avascular necrosis; severe soft tissue or bone quality compromise (previous incisions, flaps, or bone cysts); skeletal immaturity; and high physical demands (laborer, running, jumping).10,16

Keys To Appropriate Preoperative Planning

When it comes to initial radiographs of the ankle, surgeons should evaluate these for degenerative arthritis, quality of bone and osseous alignment. This evaluation must include weightbearing anteroposterior, lateral and mortise ankle views. If proximal deformities are a concern, surgeons should obtain tibio-fibular and long leg axial views to assess overall alignment. One should also consider concerns about knee and hip pathology or malalignment before proceeding with an ankle replacement.

   A computed tomography (CT) scan is recommended prior to surgery to evaluate the quality of bone, paying specific attention to any extent of cystic lesions within the tibia or talus as well as adjacent joints. Experience has shown that although the extent of arthritis and subchondral cysts may seem minimal on two-dimensional radiographs, they are often magnified on a CT scan, which can alter surgical planning. If concomitant hindfoot arthrosis is present, an arthrodesis may be beneficial to first provide a stable, plantigrade foot.

   Furthermore, one must test soft tissue and ligamentous structures to ensure their competence to constrain the implant. Otherwise, surgery may result in a poor outcome. A Telos stress ankle exam (Austin & Associates, Inc., Telos Medical) of both the lateral collateral and deltoid ankle ligaments often serves this purpose.

   It is routine to obtain non-invasive arterial Doppler studies to evaluate arterial perfusion. We typically order ankle-brachial indices, pulsed volume recordings, toe pressures and transcutaneous oximetry. If these are abnormal, surgery is contraindicated.

   One must assess the medical condition of the patient prior to surgery. Before surgery, address any major medical issues, such as cardiopulmonary conditions, and smoking. We also consult with infectious disease specialists to treat any underlying infections — such as a urinary tract infection or respiratory infection — that may place the patient at risk for possible implant infection.16

   Lastly, one would perform a physical therapy evaluation preoperatively to assess the patient’s ability to maintain a non-weightbearing gait. We consider this a key factor in obtaining a successful outcome.

What We Have Learned From Our Experience

We started performing ankle replacement surgeries at our institution in 1998. Since that time, we have performed over 100 total ankle replacement surgeries. The initial implanted device was the Buechel-Pappas implant (Endotec). Although this implant never received FDA approval, we did see early patient satisfaction with this device.

   We began using the Agility total ankle device shortly after its approval by the FDA. With minimal data available at the time, we were uncertain of the implant’s long-term durability. Within the first two to three years following surgery, patients were satisfied with decreased pain and a preservation of ankle motion. We experienced some hardware problems at three to four years following surgery. Common complications we encountered included: talar and tibial component subsidence and osteolysis; prosthesis loosening; and periprosthetic fracture. These complications lead to poor patient satisfaction and increased failure rates. As a result, we decreased the number of TARs in the early 2000s and performed more ankle arthrodesis procedures.

   Recently, with the approval of the STAR system in the U.S., we have increased the number of TAR procedures at our institution. The STAR has now become our preferred device. The advancements of the improved device include a cementless, low profile design requiring minimal bone resection and a modification of the instrumentation set.

   The reproducible stepwise surgical approach facilitates the ability to effectively and accurately prepare the joint for implantation. First, the surgeon ensures the tibial component is tightly seated into dense subchondral bone. This allows stronger fixation.
Secondly, the talar component is designed to bear weight on five surfaces. This increases the weightbearing surface area and allows for increased bony in-growth.

   Lastly, because the STAR implant is the only mobile-bearing device on the market, it effectively reduces torsional stress against the tibial and talar components. This significantly reduces the possibility of loosening.

   We have also found the Salto Talaris total ankle to be promising because it also requires minimal bone resection. The STAR and Salto Talaris devices are our current ankle implants of choice. The Agility total ankle still remains a viable option but we have relegated its use to revision surgery rather than using it as a primary implant.

In Conclusion

Although total ankle replacement surgery had less than desirable outcomes in the past, newer designs and extensive patient follow-up allow a compelling argument for total ankle replacement versus ankle arthrodesis. Similar to other foot and ankle procedures though, one must ensure careful patient selection and employ appropriate preoperative planning.

   In addition, surgeons should have the proper training and experience to perform these technically demanding procedures. Researchers have reported that the percentage of complications decreases significantly with greater surgeon experience.17,18 With four ankle implants available, one must consider each device’s specific designs and the consideration for revision surgery, if necessary. In the U.S., total ankle replacement surgery is safe, efficacious and a more cost-effective alternative to ankle fusion.19

   Dr. Mendicino is the Chairman of the Division of Foot and Ankle Surgery at the Western Pennsylvania Hospital in Pittsburgh. He is a Fellow and Past President of the American College of Foot and Ankle Surgeons.

   Dr. Catanzariti is the Director of Residency Training in the Division of Foot and Ankle Surgery at The Western Pennsylvania Hospital in Pittsburgh. He is a Fellow of the American College of Foot and Ankle Surgeons.

   Dr. Peterson is a second-year resident in the Division of Foot and Ankle Surgery at the Western Pennsylvania Hospital in Pittsburgh.


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   For further reading, see “Inside Insights On Ankle Replacement Surgery” in the March 2008 issue of Podiatry Today.

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