Total Ankle Arthroplasty

Chapter 10 Total Ankle Arthroplasty

Although many orthopaedic surgeons abandoned ankle arthroplasty because of high failure and complication rates, the continued interest in alternatives to ankle arthrodesis for ankle arthritis has led to a renewal of interest. The development of contemporary designs more compatible biomechanically with the anatomy and kinematics of the ankle, improved techniques and instrumentation, and the introduction of biological ingrowth for component fixation have led to a profusion of studies evaluating the design, technique, and outcomes of total ankle arthroplasty.

Development of Total Ankle Arthroplasty Systems

Since the first report of total ankle arthroplasty in the 1970s, more than 20 total ankle arthroplasty systems have been introduced. The first-generation, cemented, constrained designs were very stable but required extensive bony resection for implantation and frequently failed because of loosening, subsidence, and extensive osteolysis. Second-generation, less constrained implants required less bone resection and did not require cement fixation; because shear forces and torsion at the bone-prosthesis were reduced, loosening was less frequent. However, increased polyethylene wear and failure compromised the stability of the components, often leading to painful impingement and subluxation or complete dislocation of the components. Contemporary, third-generation, semi-constrained total ankle systems consist of three components: a metallic baseplate that is fixed to the tibia, a domed or condylar-shaped metallic component that resurfaces the talus, and an ultrahigh-molecular-weight polyethylene bearing surface interposed between the tibial and talar components. Systems in which the polyethylene component is locked into the baseplate often are referred to as “two-piece” or “fixed-bearing” designs, whereas those with the polyethylene component not attached to the baseplate are called “three-piece” or mobile or meniscal bearing systems. Currently, five total ankle arthroplasty systems have been approved for use in the United States by the Food and Drug Administration (FDA), with another in final clinical trials (Table 10-1). Other systems are in widespread use in Europe and Asia (e.g., HINTEGRA, Newdeal SA, Lyon, France; TNK, Kyocera Corporation, Japan; BOX, Finsbury Orthopaedics, Leatherhead, Surrey, UK).

TABLE 10-1 FDA-Approved Total Ankle Arthroplasty Systems

Agility (DePuy, Warsaw, IN)
Agility Revision—May 2002—for revision of primary Agility arthroplasty
Agility LP—2006—talar component completely covers talus; cemented
December 1992 Requires syndesmotic arthrodesis, semi-constrained talar component; designed to be used with cement
INBONE (Wright Medical, Arlington, TN) November 2005 Modular tibial stem, intramedullary instrumentation-alignment
Salto Talaris (Tornier, Saint Ismier, France) November 2006 Conical talar component, medial radius of curvature greater than lateral; two-piece anatomical, fixed-bearing implant
Eclipse (Integra Life-sciences, Plainsboro, NJ) November 2006 Medial approach for insertion, cylindrical cuts for tibia-talus; use currently on hold
STAR (Waldermar Link, Hamburg, Germany) May 2009 Only approved three-component system, tibial fixation with two 6.5-mm cylindrical bars
Mobility (DePuy International, Leeds, UK) Pending Three-component design, anterior window for tibial stem, in clinical trials vs. Agility LP

Adapted from Cracchiolo A 3rd, DeOrio JK: Design features of current total ankle replacements: implants and instrumentation, J Am Acad Orthop Surg 16:530, 2008.

Design Rationale

The development of an implant system that mimics the normal anatomy and biomechanics of the ankle and achieves success rates similar to those of hip and knee arthroplasty has been hampered by several anatomical features of the ankle joint: (1) the ankle has significantly less contact area between joint surfaces than the hip or knee; (2) the ankle experiences 5.5 times body weight with normal ambulation, compared with 3 times body weight at the knee; and (3) the articular cartilage surface of the ankle is uniformly thinner than that of the knee.

The biomechanical concepts that have resulted in the most recent generation of ankle arthroplasties are somewhat beyond the scope of a surgical-oriented textbook; however, the number and variety of implants on the market demand a familiarity of basic principles of component design.

Fixed-Bearing Versus Mobile-Bearing Design

Most modern implants fall into two basic groups: those with the polyethylene component fixed rigidly to the tibial component (Fig. 10-1A) and those with a mobile polyethylene component that has the ability, at least in theory, to move under the tibial component to adapt to changes in joint forces (see Fig. 10-1B). Mobile-bearing designs are used most commonly in Europe and have a long history of outcomes from which they can be evaluated. Another theoretical advantage of these designs is the “forgiveness” of the implant, which allows small variances in alignment to be compensated for by a reorientation of the prosthesis to accommodate the joint forces. The ability of the polyethylene component to move should, in theory, keep the articulation between the talar component and the polyethylene component more congruent and less likely to edge load and have advanced wear. In experienced hands, however, there is a question of how much the polyethylene component actually moves under the tibia. Barg et al. found very little anteroposterior movement of the talar component under the tibia in follow-up radiographs of a three-component, mobile-bearing design and noted that the prosthesis functioned largely like a fixed-bearing design, but with a possible advantage of allowing an individualized position of the polyethylene insert in response to individual soft tissue loads produced by different ankle joint configurations. Aside from the STAR ankle implant (Fig. 10-2), implants approved for use in the United States are fixed-bearing designs (see Table 10-1).

Proponents of fixed-bearing designs suggest that the normal ankle joint, as opposed to the knee, has a more stable central axis of motion and less need for an additional degree of freedom of motion. Backside polyethylene wear against the tibial component is a major concern with mobile-bearing designs and less with fixed designs. Attention to detail in the proper alignment of the prosthesis along the mechanical axis of the limb has been suggested to prevent excessive wear.

Preoperative Evaluation

A thorough understanding of the patient’s medical history and review of systems is important in the decision-making process and the consideration of the patient for total ankle arthroplasty. Systemic diseases such as diabetes, inflammatory arthritis, chronic obstructive pulmonary disease, and peripheral vascular or heart disease may adversely affect the outcome and healing of the incision. Conditions such as sleep apnea, malnutrition, vitamin D deficiency, and depression are associated with decreased functional outcomes and poor results. We do not perform elective total ankle arthroplasty in active smokers. It must be clear that the ankle joint is indeed the cause of the patient’s primary complaint. Many of these patients have adjacent joint disease that might also need to be treated before or at the time of surgery. Selective injections of lidocaine are helpful in accurately identifying the painful pathological process. A complete assessment of the limb is important. A lumbar spine pathological process with sciatica and radicular lower extremity pain or degenerative disease of the hip or knee may cause a change in the management plan. Patients with combined knee and ankle arthritis and deformity often are best managed by correction of the knee deformity first, followed by the ankle replacement.

A thorough evaluation of the neurovascular status of the limb is important, and any concerns should prompt a formal vascular evaluation. The patient’s gait should be evaluated for limp, and any alterations of knee or hip motion to compensate for the arthritic ankle and limb length difference should be assessed. The standing evaluation is important for a clinical assessment of the alignment of the ankle and hindfoot. Is there a supramalleolar deformity that must be corrected? Is the hindfoot well aligned, or is there a component of varus or valgus? Clinical assessment of the gastrocsoleus complex and the Achilles tendon is important. The Silfverskiöld test for selective gastrocnemius tightness might reveal a contracture that is independent of ankle range of motion and that must be released intraoperatively. Coetzee and Castro demonstrated the inability to distinguish true range of motion of the tibiotalar joint on clinical examination and proposed a radiographic evaluation of the range of motion preoperatively. Nonetheless, an idea of sagittal plane range of motion is important. Overall hindfoot motion is important as well. A stiff, arthritic hindfoot might be the difference between choosing arthroplasty or arthrodesis. Strength testing of the leg motor groups should not reveal major deficits that would impair the outcome. The anterior skin should be stable and without lesions that would impair the healing of the surgical incision.

At a minimum, standing radiographs of the ankle in anteroposterior, lateral, and mortise views should be obtained. Any suspicion of proximal limb malalignment should be evaluated with standing lower extremity films. Because an accurate assessment of the alignment of the hindfoot is not possible with standing films of the ankle, Frigg et al. described a hindfoot alignment view (Fig. 10-4) that gives a better appreciation of overall alignment and helps to determine if an adjunctive procedure is needed to improve the alignment of the foot distal to the ankle joint. Radiographic evaluation should include assessment of the quality of the bone stock, coronal plane alignment of the ankle with supramalleolar deformities or joint incongruencies, the presence of osteophytes requiring removal, adjacent joint arthritis or malalignment that requires correction, calcaneal pitch angle as a predictor of gastrocsoleus contracture, and the presence of major cysts or defects that will need grafting.

Total Ankle Arthroplasty or Ankle Arthrodesis for Ankle Arthritis

Ankle arthrodesis (see Chapter 11) has long been the “gold standard” for the surgical treatment of moderate to severe ankle arthritis. It is, therefore, reasonable to ask if there is a compelling reason to pursue total ankle arthroplasty as a treatment option for patients with ankle arthritis. Although the patient satisfaction rate after ankle arthrodesis is fairly high, there are certainly circumstances in which arthrodesis might not be the best procedure, including preexisting subtalar or other hindfoot arthritis, contralateral hindfoot or ankle arthritis, and hip or knee impairment such that motion through the ankle joint may be beneficial to the overall limb and patient function.

No level I studies have directly compared the two procedures, and reports in the literature are contradictory (Table 10-2). Longer-term studies are needed to compare these two procedures, but currently available data seem to indicate similar outcomes for patients with arthroplasty and arthrodesis suggesting that careful patient selection is mandatory for the success of either of these procedures in the treatment of ankle arthritis.

Total Ankle Arthroplasty

Technique 10-1

Jun 5, 2016 | Posted by in ORTHOPEDIC | Comments Off on Total Ankle Arthroplasty
Premium Wordpress Themes by UFO Themes