Ankle Arthroplasty

Anatomy and Physiology

Having in-depth knowledge of the anatomy and biomechanics of the ankle joint is essential for appropriate patient and implant selection, surgical intervention, and successful outcomes. The ankle joint is a hinged synovial joint comprising the tibial plafond, the medial malleolus of the tibia, the lateral malleolus of the fibula, and the talus. These structures all articulate with one another, forming the ankle joint. The stability of the ankle joint is conferred by the ankle's static and dynamic stabilizers. Dynamic stabilizers of the ankle joint include the various tendons surrounding the joint, including the peroneal tendons. The static stabilizers of the ankle include the various ligamentous and osseous structures of the ankle.

Indications

TAA is indicated in patients with unilateral or bilateral end-stage ankle osteoarthritis. A healthy, low-demand, reasonably mobile patient with no significant comorbidities, normal or low body mass index, stable, well-aligned hindfoot, and robust soft tissue envelope is the ideal candidate for TTA. Wood et al denote a preserved ankle range of motion with at least 5° of dorsiflexion is also ideal.[5]

Contraindications

TAA is not recommended for patients with active infection, peripheral vascular disease, Charcot arthropathy, severe osteoporosis, osteonecrosis of the talus, peripheral neuropathy, and inadequate soft tissue envelope, as these conditions predispose the patient to implant failure or infection.[6]

Equipment

A few iterations of standard TAA implants have developed since the procedure was first described.[7][8] First-generation designs were highly constrained but required large bone cuts; they comprised 2 components with cement fixation on the tibia and talar components. The 2 components were a concave polyethylene tibial component and a convex metal (usually cobalt-chrome alloy) talar component. Some designs had the same components inverted, so the talar component was concave. First-generation implants had high loosening rates, osteolysis, subsidence, and mechanical failure.

Second-generation implants were developed to combat the large bone cuts required in first-generation, which were fixed bearing with a polyethylene bearing surface built into the talar or tibial components. Examples of second-generation implants included the Buechel-Pappas Total Ankle Replacement (Endotec, South Orange, NJ) in the United States and the Scandinavian Total Ankle Replacement (STAR; Waldemar Link, Hamburg, Germany) in Europe. This generation had more conservative bone cuts to allow for more bone preservation and were press fit. Like the first-generation models, however, there was a high failure rate due to increased polyethylene wear.

More modern third-generation implants have been designed to counter these causes of failure.[9] Examples of third-generation TAA implants include the Salto (Tornier SA, Saint Ismier, France), Hintegra (Newdeal SA, Lyon), Mobility (DePuy, Warsaw, IN), and Bologna-Oxford (BOX; Finsbury Orthopaedics, Leatherhead, Surrey, UK). These implants use a standalone polyethylene component not built into the tibial or talar components. They require minimal bone resection; however, they do require adequate balancing for implant success. These implants rely heavily on the integrity of the ligamentous structures surrounding the ankle. As implant technology has advanced, implant instrumentation has been refined, often incorporating cutting jigs. Preoperative computed tomography planning and patient-specific instrumentation in 3-dimensional printed cutting guides have evolved to reduce operative time and fluoroscopic exposure without compromising implant position.[10]

Personnel

To perform a TAA safely, the minimum operative team required includes:

• Anesthetist or anesthesiologist
• Surgical technician or scrub technician 
• Operating room circulating nurse
• Foot and ankle surgeon
• Surgical assistant—either a physician's associate or first assist
• Recovery nurse
• Implant device representative (provides the necessary implants and serves as a reference when using the equipment)

Preparation

Patient History 

Before considering TAA for the treatment of end-stage osteoarthritis, all patients should undergo a comprehensive history and physical examination. This should include obtaining the patient’s past medical history, past surgical history (especially any surgery to the ankle in question), current medications and allergies, history of prior trauma to their ankle, and all previous interventions and treatments.  

Clinical Assessment 

A thorough clinical assessment should take place, including a complete physical examination, gait assessment, active and passive ankle range of motion, vascular status of the limb, ankle stability, and skin condition.  

Imaging Modalities 

Ankle x-ray 

• Weight-bearing anterior to posterior, lateral, and oblique plain films are obtained before surgical intervention to assess the bony elements of the ankle and allow for preoperative templating. Full leg-length radiographs may often be obtained to assess preoperative alignment.[11]   

Ankle computed tomography 

• Preoperative ankle computed tomography (CT) scans may be useful in determining bone stock before surgery. Recent advancements in implant technology now create patient-specific 3-dimensional printed cutting guides for accurate bone cuts and adequately sized implants. These require a preoperative CT scan to be completed and sent to the implant manufacturer.[11]   

Ankle magnetic resonance imaging 

• Ankle magnetic resonance images may help determine the amount of involvement, bone loss, cyst size and locations, and osteonecrosis.[11] 

Technique or Treatment

Anesthesia

General anesthesia associated with a regional nerve block, such as a popliteal fossa block, is usually used for TAA. Prophylactic intravenous antibiotics are given during the induction.

Patient Position

For TAA, the patient is usually positioned in the supine on a radiolucent operating table. A nonsterile tourniquet is applied as proximal as possible on the operative extremity. Nonsterile drapes are then applied to delineate the operative versus nonoperative fields. A large bump may be used to elevate the operative extremity.

Approach 

The tibialis anterior tendon is palpated just proximal to the ankle joint, and an anterior approach is made lateral to this tendon with a scalpel. Full-thickness skin flaps are developed and elevated using a scalpel and Metzenbaum scissors. Meticulous dissection is performed deep towards the ankle joint, protecting tendon sheaths, synovium, and medial dorsal cutaneous nerve branches. Upon encountering the extensor retinaculum, the area is incised longitudinally, avoiding disturbance or exposure of the tibialis anterior tendon sheath. The interval between the tibialis anterior and the extensor hallucis longus is developed, allowing retraction of each as needed. The anterior tibial artery and vein, along with the deep peroneal nerve, are identified and protected throughout the procedure. The joint capsule and periosteal layer are then incised, creating flaps typically tagged for repair at the end of the case.

Bone Cuts 

Once appropriate dissection and exposure have been performed, the surgeon’s preferred implant-cutting guides are used to sequentially cut the tibia and talus appropriately. While making the tibial cuts, avoid cutting the tibia too medial, as an iatrogenic medial malleolar fracture may result. As such, it is essential to be cognizant of the medial malleolus thickness before making your cut. Prophylactic pinning of the medial malleolus can be done in this stage to prevent possible iatrogenic fracture.

Trialing and Insertion of Components 

Next, the tibial and talar trials are introduced, and the sizes for the final implants are determined. Soft tissue balancing is performed, which may require multiple soft tissue releases around the joint. Guide holes are typically drilled through the trials. The final implants are press fit with or without cementation, ensuring adequate fixation in the tibia and talus. Trialing again with the trial poly liner to appropriately tension soft tissues is typically recommended. Once satisfactory tensioning is obtained, the final poly is inserted. Appropriate component positioning is determined with fluoroscopy.

Wound Closure

The surgical wound is thoroughly irrigated with sterile, warm, normal saline to remove any remaining debris from the wound bed. The extensor retinaculum is reapproximated with assistance from the prior tagging suture and closed with an absorbable, polyfilamentous suture, ensuring a water-tight seal. The deep dermal layer can be closed with an absorbable polyfilamentous suture, and superficial skin is closed with the surgeon’s preferred suture. Sterile soft dressings, including an occlusive petroleum-based gauze and 4x4 gauze, as well as a short leg splint, are applied.

Postoperative Protocol

Standard postoperative protocol assuming no ligamentous reconstructions or osteotomies were included in the procedure is as follows: 

• Short leg splint for 2 weeks for soft tissue rest 
• Removal of sutures and splint at 2 weeks, begin ankle range of motion 
• Non-weight bearing for a total of 4 weeks 

Postoperative x-rays should be obtained at regular intervals to assess the components, look for fractures, evaluate for loosening or subsidence, and assess the bone stock of the tibia and talus near the components. Notably, a lateral approach can be used for TAA that requires a distal fibula osteotomy, but this technique has fewer implant designs and is much less commonly used.[12]

Complications

Wound Healing

In TAA, postoperative wound complications can range from superficial to deep. Superficial dehiscence, stitch abscesses, cellulitis, and delayed wound healing are known complications. Ensuring delicate soft tissue handling using tension-reducing closing sutures during the case can decrease wound complications. A compressive dressing has been shown to reduce wound complications.[12][13]

Prosthetic Joint Infection 

The incidence of infection in primary TAA noted in the literature ranges from 0% to 13% and is more frequently seen in revision TAA compared to primary.[14][15] Prosthetic joint infections (PJIs) can be quite severe and require much more aggressive intervention for treatment. Surgical treatment of acute (within 3 weeks postoperative) PJIs is typically managed with debridement, antibiotics, polyethylene insert exchange, and retention of the prosthesis components. Surgical treatment of chronic PJIs in the setting of TAA typically includes an explant of the prosthesis and an aggressive and comprehensive debridement of the ankle and surrounding tissues with the insertion of an antibiotic-impregnated spacer. Supplementing an aggressive antibiotic regimen, either oral or intravenous, for an extended time is typically warranted; they may require serial debridements and complex revision surgery after clearing the infection. As of 2023, there is a lack of diagnostic criteria specific for PJI after TAA, and instead, clinical and laboratory tests frequently used in hip and knee arthroplasty are generally used in the setting of TAA.[16]

Intraoperative Fracture 

Iatrogenic medial malleolus fracture is the most common intraoperative fracture during TAA. They usually occur due to fracture propagation through the narrow bone bridge formed after the tibial cuts are made, especially if the cuts are more medial.[17] Prevention of this potentially detrimental complication is accomplished through prophylactic screw fixation of the medial malleolus with retention of the screws postoperatively versus Kirschner wire fixation until the final implants are in.[18]

Other Common Postoperative Complications 

Other complications include: 

• Sensory deficits or nerve injury [19] 
• Component loosening or subsidence [20] 
• Talus component fails more commonly than the tibial component due to loosening [20]
• Osteolysis [21] 
• Iatrogenic tendon injury or postoperative tendinitis [21][22]
• Polyethylene displacement or subluxation [20]
• Gutter impingement [21][22] 
• Arthrofibrosis [21][22]

Clinical Significance

TAA is a fast-growing treatment modality for complex end-stage ankle osteoarthritis. Compared to ankle arthrodesis, arthroplasty preserves the motion of the ankle joint, allowing for a more physiologic approach to treatment.[23] Preventing abnormal gait with ankle arthroplasty can preserve the other joints in the extremity.  

Enhancing Healthcare Team Outcomes

Healthcare professionals responsible for supervising patients with end-stage ankle arthritis must thoroughly understand the total ankle arthroplasty procedure and the specific indications and contraindications associated with it to correctly identify suitable candidates for this form of treatment. Effective TAA relies heavily on a multidisciplinary team approach to ensure optimal patient outcomes and safety. Foot and ankle surgeons and podiatrists should provide transparent guidance on expectations and postoperative care. Educating patients on weight-bearing ability, pain management, perioperative medical management, wound care, and postoperative rehabilitation is imperative to promote rapid recovery and minimize complications. Perioperative nurses are responsible for coordinating and monitoring patients before, during, and after surgery, promptly informing clinicians of any changes in vital signs or mental status. Additionally, nurses and advanced practitioners should support clinicians in educating patients and their families about expectations regarding the procedure. The hospital pharmacist should assess the patient for potential drug interactions and allergic reactions and assist with proper dosing for pain management during the patient's hospital stay. Postoperative rehabilitation is typically facilitated by a physical therapist, with rehabilitation protocols put in place.

Regular follow-up office visits, clinical evaluations, and sequential postoperative imaging are essential to quickly identify and address potential postoperative complications. Interprofessional communication and care coordination are critical for seamless patient-centered care in TAA. Achieving the best outcomes requires a coordinated effort from the entire healthcare team. This integrated approach improves clinical outcomes, enhances patient satisfaction, and improves team performance.