Ankle Arthritis: Part II. Total Ankle Arthroplasty

Thos Harnroongroj, MD

Constantine A. Demetracopoulos, MD

Dr. Demetracopoulos or an immediate family member has received royalties from Exactech, Inc.; is a member of a speakers’ bureau or has made paid presentations on behalf of Exactech, Inc., Integra LifeSciences, Paragon 28, Royal Biologics, Stryker, and Wright Medical Technology, Inc.; serves as a paid consultant to or is an employee of Exactech, Inc., Integra LifeSciences, Paragon 28, Royal Biologics, RTI Surgical, Stryker, and Wright Medical Technology, Inc.; and has received research or institutional support from Integra LifeSciences. Neither Dr. Harnroongroj nor any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this chapter.

This chapter is adapted from Smith WB, Berlet GC: Ankle arthritis: Part II. Total ankle arthroplasty, in Chou LB, ed: Orthopaedic Knowledge Update: Foot and Ankle 5. Rosemont, IL, American Academy of Orthopaedic Surgeons, 2014, pp 129-143.

ABSTRACT

At present, total ankle arthroplasty (TAA) has evolved to result in improved clinical outcomes and survivorship for the treatment of end-stage ankle arthritis. Recent evidence suggests equivalent pain and improved function after TAA compared with ankle fusion. To achieve a successful TAA, there are important factors to take into consideration such as patient selection, operative techniques, alignment and ligament balancing, and prompt recognition and treatment of complications. This chapter provides a review of the evolution of TAA designs, the indications and contraindications, a brief review of the surgical technique including how to address deformity of the ankle and when to perform concomitant procedures, and a review of common complications. We also review recent literature on the outcomes of TAA, including revision TAA, and salvage arthrodesis.

Introduction

Over the past 10 years, an increasing number of patients with end-stage ankle arthritis have been treated with total ankle arthroplasty (TAA). This trend is due to many factors, including innovations in implant design, improvements in surgical instrumentation, a better understanding of surgical techniques for deformity correction, and promising early to midterm results with modern prostheses. The first reported ankle arthroplasty was in 1970, and the authors subsequently published their initial results of 12 patients in 1973.¹ The implant consisted of a tibial stem and polyethylene talar-replacing component that necessitated a subtalar fusion. The ball-in-socket design of the first total ankle implant was modeled after hip implant design, and results were poor.

Early studies of first-generation ankle arthroplasty demonstrated promising results, but midterm follow-up revealed evidence of substantial radiographic loosening and high failure rates.² Many initial ankle prostheses were designed as a simple, constrained hinge. Motion was allowed only in the sagittal plane. These early implants necessitated substantial bone resection, thus placing the components in softer, metaphyseal bone. In addition, most early implants were cemented. These highly constrained designs transmitted significant forces to the bone-implant interface, which led to early loosening, implant subsidence, and failure.²

Subsequent designs were much less constrained, such as the New Jersey low-contact stress prosthesis (DePuy), the Newton prosthesis (Stryker Howmedica Osteonics), and the Smith prosthesis (Dow Corning Wright). These implants were designed to rely on the stability of the ligamentous envelope of the ankle joint. However, this proved insufficient, and these implants also suffered from a high incidence of impingement, and significant early failure.²

The current generation of TAA implants emphasize limited bone resection, improved fixation to the surrounding bone for initial stability and to encourage bony ingrowth, and seek to restore the physiologic constraint and articulation of the ankle joint. In addition, there are advances in revision TAA systems which compensate for bone loss both on the tibial and talar side. Current TAA implants have two common features: first, all have porous coated surface for enhancing bone ingrowth, and second, all are made of titanium alloy with a cobalt-chrome-polyethylene articulation.³

In the United States, there are nine TAA systems currently available: the Scandinavian Total Ankle Replacement ([STAR] Stryker) (Figure 1), the Salto-Talaris and Salto XT Total Ankles, the Cadence Total Ankle (Integra LifeSciences) (Figures 2 and 3), the Infinity, INBONE II, and INVISION implants (Wright Medical Technology) (Figures 4, 5, 6), the Trabecular Metal Total Ankle (Zimmer) (Figure 7), and the Vantage Total Ankle (Exactech) (Figure 8). All fixed-bearing TAAs in the United States are FDA cleared for cemented use, and the STAR is a mobile-bearing implant FDA approved for use without cement.

FIGURE 1 Scandinavian Total Ankle Replacement (STAR), Stryker.

FIGURE 2 Salto-Talaris Total Ankle (Tornier).

FIGURE 3 The Cadence (Integra Life Sciences

FIGURE 4 INBONE II total ankle (Wright Medical).

FIGURE 5 The Infinity (Wright Medical).

FIGURE 6 The INVISION (Wright Medical).

FIGURE 7 The Trabecular Metal Total Ankle (Zimmer).

FIGURE 8 The Vantage (Exactech).

Design Issues and Rationale

Anatomy and Biomechanics

The ankle joint consists of three bony interactions: the tibia, fibula, and talus. The morphology of each bone affects the function and relationship of the ankle joint.

Many patients who present with ankle arthritis will also demonstrate radiographic and clinically significant adjacent joint arthritis in the hindfoot, most commonly the subtalar joint. Also, adjacent joint arthritis is known to significantly progress with ankle arthrodesis. The biomechanical rationale for increased wear in adjacent joints was elucidated in a 2009 study, which showed that motion in the subtalar joint in the sagittal, coronal, and transverse planes changes to move in the opposite direction when compared with healthy ankles.⁴ The complication of adjacent joint arthritis has fueled the search for ankle fusion alternatives.

The current generation of implants have sought to address the shortcomings of initial implants. Improved materials and fixation techniques were implemented. By minimizing resection, the implants are placed on stronger, subchondral bone. In addition, by improving initial fixation and ingrowth, implants may be successfully placed without cement. Modern implant designs are semiconstrained, which reduces the stress at the bone-implant interface, and has been successful in improving midterm survivorship.

Because the ankle allows for both gliding and rolling motion, implants are designed to accommodate complex three-dimensional ankle motions. Implant use entails a balance of compromises. Fixed-bearing devices offer inherent stability but sacrifice certain planes of motion, particularly rotational. Mobile-bearing devices allow for more rotational motion, thus decreasing stress to the implant, but they also can reduce stability, allow for possible bearing impingement, edge loading of the polyethylene, and create the potential for backside polyethylene wear.

Current ankle prostheses can strike the necessary balance between providing implant stability and decreasing stress transfer to bone. On the tibial side, most implants of the current generation emphasize a similar approach of minimizing the amount of bone resection to allow for stable fixation on the cortical rim of the distal tibia. Additional stability of the tibial component is achieved with either a keel, barrels, pegs, a cage, or a stem.

The complex anatomy of the talus poses challenges to both implant designers and surgeons. Talar anatomy features complex three-dimensional conical wedges. The radii of curvature on each side of the talus (medial, lateral, anterior, and posterior) all differ. The axis of rotation of the talus has been described as having a changing instant center of rotation,⁵ with the primary axis of rotation correlated with the transmalleolar plane and externally rotated 23°.⁶ To further confound the mechanism, the ankle also rotates about 5° in the transverse plane.⁷ Current primary total ankle implants have a “resurfacing” talar component. Most implant systems do so by making an anterior and posterior chamfer after performing a cut on the top of the talus. Two current implants create a curved surface on the talus, which allows for perpendicular loading of the implant against the bone, with the intention of minimizing the effect of shear forces.

Previously, resurfacing the medial and lateral facets was believed to help reduce the incidence of gutter impingement. However, current implants, which do not resect the bone of the medial and lateral talus to spare bone, do not have a higher incidence of gutter impingement postoperatively.

The blood supply of the talus is known to be sensitive to injury and surgical manipulation. Each technique puts different vascular structures at risk. Tennant et al conducted a cadaveric injection study and reported that INBONE subtalar drill hole had a risk of transection of artery of the tarsal canal. While the lateral approach of the Trabecular Metal Total Ankle had a risk of injury to the first perforator of peroneal artery, the STAR had a risk of injury to the deltoid branches.⁸^,⁹ Ultimately, how our surgical approaches and techniques affect in vivo blood supply to the talus is not known, and it is unclear how these effect influence survivorship of the TAA implants.

Indications

Unprecedented amount of data on ankle arthroplasty are becoming available. As this information is reviewed, indications and techniques will undoubtedly evolve as well. TAA is indicated in patients with end-stage ankle arthritis who have failed nonsurgical management. Posttraumatic arthritis is the most common etiology of ankle arthritis, which includes patients with a history of fracture and ankle instability. Other common causes include inflammatory arthropathies, gout, avascular necrosis, and primary ankle osteoarthritis.

Patients who have bilateral ankle arthritis and those who already demonstrate significant arthritis in the hindfoot are excellent candidates for TAA. Patient age is a subjective matter in terms of indications for TAA. Traditionally it was thought that only elderly patients with low physical demands should be offered TAA. Early studies reported that implant survivorship and functional outcomes are decreased in younger patients undergoing TAA.¹⁰^,¹¹^,¹²^,¹³ More recent studies, however, have shown equivalent survivorship outcomes among younger and older patients.¹⁴^,¹⁵ Because there are no hard and fast guidelines, it is important during the informed consent process that patients understand the risks inherent to TAA and determine if those risks fit within their expectations for demand and lifestyle.

Patients with rheumatoid or other inflammatory arthropathies may have foot and ankle joint involvement. Following ankle fusion, the forces across the hindfoot and midfoot joints increase, which may precipitate additional problems. Ankle arthroplasty may be considered in these patients to help decrease forces across the hindfoot and midfoot.¹⁶^,¹⁷^,¹⁸

Patient expectations for return to activity must be discussed. A patient should be counseled that return to activities is encouraged but that lower impact activities are necessary. Return to impact activities presents a challenge; several studies that have looked at return to sport activity after ankle arthroplasty have shown that lower impact activities are safe and may be encouraged.¹⁹^,²⁰

In addition to age and activity issues, patients must have sufficient bone stock to allow for implantation of the prosthesis. They must also have a healthy soft-tissue envelope that allows for adequate coverage after procedure completion. Soft-tissue compromise or significant vascular disease may prompt discussion of alternative options.

Contraindications

Contraindications to TAA include active infection, Charcot or neuropathic joint involvement, complete paralysis of the affected limb, large area of osteonecrosis of the talus or distal tibia, vascular insufficiency, poor soft tissue without good reconstructive options, and severe deformities that cannot be corrected.

An MRI should be considered for patients considering ankle arthroplasty who have a history of talar osteonecrosis or infection. The findings will likely provide additional information about the viability of the bone and whether joint arthroplasty should be considered. Partial osteonecrosis in a section that will be removed with the bone cut is not a strict contraindication to TAA. More extensive bone involvement should be considered a contraindication. A CT scan is beneficial to identify cysts in the bone that may need to be bone grafted at the time of TAA procedure.

Relative contraindications include ligament instability, history of infection, diabetes, morbid obesity, osteoporosis, severe malalignment, poor soft-tissue quality, smoking, and neuropathy. Patients who have high-demand employment or activity requirements may require an ankle arthrodesis.

An extensive preoperative consultation is essential to help patients understand if TAA is an option. During an in-depth conversation with a patient, numerous topics may present themselves that will help to introduce possible treatment options. Not all patients with ankle arthritis are candidates for TAA.

Surgical Treatment

Techniques

At the author’s institute, the procedure is performed with a long-acting spinal, in combination with a popliteus and saphenous nerve block. The patient is then positioned supine on a radiolucent surgical table. The surgical hip is bumped to allow for the foot to be positioned straight. A thigh tourniquet is applied and the surgical limb is prepped and draped to thigh level.

An anterior approach is the most commonly used incision for TAA. The incision should start approximately 10 cm proximal to the ankle joint and proceed distal in a curvilinear fashion to end distal to the talonavicular joint. An adequate incision should be used to decrease tension on the skin during retraction and allow for good visualization. The interval between the anterior tibialis and extensor hallucis longus (EHL) is developed. Attention is given to the anterior neurovascular bundle, which should be mobilized, protected, and retracted laterally with the EHL. Minimal handling of the tissue and judicious use of retractors are warranted to limit undue pressure to the soft tissue. Excessive retraction can lead to wound edge necrosis, and wound complications have been reported to be as high as 28%.²¹^,²²^,²³

After the approach has been developed to the level of the ankle, a complete débridement is done to expose the
osseous architecture. Anterior osteophytes at the distal tibial plafond can be removed to allow visualization of the joint. The main consideration of adequate exposure of the joint is to completely visualize the medial and lateral gutters of the ankle. Ankle deformity must be corrected prior to making the cuts. The talus must be able to come to a neutral position within the ankle mortise. In addition, the ankle must be able to dorsiflex to neutral before making any bony resection. The cuts are completed per the manufacturer-suggested techniques based on the implant being placed.

Key areas of concern outside of the limited soft-tissue envelope include the anterior tendons, which must be protected judiciously during the cutting of the bone. They are at risk for damage by the sagittal saw and must be repaired if accidentally injured. Also, special attention must be given to the posterior medial corner because the posterior neurovascular bundle and posterior tibial tendon are at risk. The flexor hallucis longus is at risk at the center-posterior aspect of the tibial cut. If any of these posterior structures are damaged, further exploration is necessary to determine if the posterior tibial artery and tibial nerve were also injured so that prompt repair may be performed.

After the prosthesis has been implanted, a meticulous layered closure is completed. The patient is then placed into a well-padded splint, taking care to avoid pressure upon the common peroneal nerve proximally and to place the ankle in a neutral position. Care should be taken to avoid applying undue pressure on the incision line after the dressing is applied.

Approaches

Currently, the anterior approach to the ankle is the approach for which there is the most relevant literature for evaluation. A newer implant that was released in 2013 (the Trabecular Metal Total Ankle) uses a lateral, transfibular approach to the ankle joint. The posterior approach for TAA is another option. Because the posterior soft tissue of the ankle is often more robust, it seems to be an attractive alternative in the patient who is a risk for poor wound healing anteriorly. A limited number of anecdotal and case reports mention the posterior approach for the current generation of implants.²⁴ Because the current implant systems are not designed for placement of the implant from a posterior approach, this approach has limited appeal at this time.

Concomitant Procedures

Ankle arthritis usually does not exist as a lone pathology. Additional issues typically affect patients with this condition, some of which may be related to the underlying arthritis. Retained hardware may need to be addressed when posttraumatic arthritis exists, for example. Adjacent joint arthritis, deformities, equinus contractures, and bone stock issues all may need to be considered when thinking about TAA. Deformity of the foot must also be addressed to assure a well-balanced foot underneath the implant.

Hardware removal is a common additional procedure when TAA is performed. The anticipated removal instruments must be available during these procedures. Based on the implant being used, more or less hardware may be removed after joint preparation. Residual bone defects from hardware removal must be considered stress risers. If the surgeon concludes that risk exists for a periprosthetic fracture, prophylactic stabilization must be placed, or, in some cases, a stemmed implant can bypass the anatomy at risk.

If there is residual ankle equinus after the implant has been positioned, a SilfverskiÖld test is performed intraoperatively to determine whether a gastrocnemius recession will be effective in restoring dorsiflexion. Oftentimes, however, a percutaneous tendo-Achilles lengthening or gastrocnemius recession is necessary to achieve sufficient dorsiflexion motion in patients with long-standing equinus contractures. In these cases, however, there is a risk of plantarflexion weakness that must be considered.²⁵ There is a literature comparing the clinical outcomes included range of motion between TAA with triceps surae lengthening and TAA alone. The results demonstrated that TAA with triceps surae lengthening had significantly better total and dorsiflexion range of motion of the ankle than TAA alone at 1 year postoperative follow-up. The other functional outcomes were improved significantly from pre-to postoperative period in both groups²⁶ Patients should be counseled that ankle range of motion will not return to normal.²¹

In regard to adjacent joint arthritis, it is useful to ascertain preoperatively whether the adjacent joints are a significant source of pain. Often, fluoroscopic-guided injections can assist in determining if adjacent joints may be contributing to pain. Several studies have shown progression in adjacent joint arthritis after TAA.²⁷^,²⁸ However, this rate is far slower than what has been reported previously after ankle arthrodesis.²⁹^,³⁰ Patients with subtalar arthritis will often report less pain in that region after TAA. Concomitant subtalar arthrodesis may result in significant injury to the blood supply of the talus and should be performed only when absolutely necessary. A staged approach is favored. If concomitant subtalar arthrodesis is performed, care should be taken to prepare the posterior facet only and not disrupt the vessels within the sinus tarsi.³¹ Gross et al observed the outcomes of the secondary arthrodesis after TAA. The
results revealed that the secondary hindfoot arthrodeses were performed only in 26 of 1,002 TAA patients (2.6%). There were two delayed union (7.7%) and two nonunion (7.7%). Pain and functional outcome scores improved significantly. Comparing of union rate between subtalar arthrodesis with TAA and with ankle arthrodesis, subtalar arthrodesis with TAA had significant better fusion rate and similar time to fusion.³² Lewis et al reported the clinical outcomes of 70 patients with hindfoot fusion before, after, or at the time of TAA compared with 334 patients who underwent total ankle replacement (TAR) alone. He demonstrated the inferior outcomes in regard to pain and functional results of the TAA with hindfoot fusion.³³ Cody et al³⁴ conducted a prospective database review of the patients who underwent primary TAA with a minimum 5-year follow-up. She found that ipsilateral hindfoot arthrodesis was one significant factor led to revision of TAA. The results of Lewis and Cody raises possible concern that hindfoot arthrodesis may alter the biomechanics of the TAA and affect the long-term clinical outcomes and survivorship of TAA.

Additional procedures in the foot can be done in conjunction with TAA to balance the foot. Calcaneal osteotomies, procedures to the first ray, tendon transfers, and ligament repairs or reconstructions may be necessary. With potential complications in mind, additional procedures should be carefully considered during the planning phase to allow for placement of incisions and soft-tissue management.

A thorough limb alignment evaluation and deformity analysis is critical when planning TAA surgery. In addition to obtaining standard three-view radiographs of the foot and ankle, long leg and hindfoot alignment views may also be needed. Weight-bearing CT images also can be beneficial when ascertaining the extent of deformity before surgery.

Traditionally, it was believed that coronal plane deformities exceeding 10° to 15° should be treated with ankle arthrodesis instead of TAA secondary to increased failure rates.³⁵^,³⁶^,³⁷ More recent literature has refuted these claims. Numerous studies have shown equivalent outcomes for deformities of between 15° and 30°.⁷^,¹⁰^,³⁸^,³⁹^,⁴⁰ Studies which show equivalent results in patients with mild and severe deformity also demonstrate no difference in postoperative alignment between the two groups, thus highlighting the need to correct the deformity at the time of surgery.

For treatment of varus ankle deformities, the most common adjunctive procedures are lateral displacing calcaneal osteotomy, deltoid ligament release or medial malleolar osteotomy, and lateral ligament reconstruction.⁷^,³⁸^,³⁹^,⁴⁰^,⁴¹^,⁴² If the talus will not reduce after complete deltoid release, further attention should be paid to debriding the gutters, particularly the lateral gutter, and a portion of the lateral distal tibial plafond may need to be removed to allow the talus to tilt back into a neutral position.⁴³ In addition, a dorsiflexion osteotomy of the first metatarsal, as well as a peroneus longus to brevis transfer may also be beneficial in the varus ankle. It is essential to achieve a plantigrade foot when planning TAA.

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