Anterior Approach Total Ankle Arthroplasty with Patient-Specific Cut Guides

Abstract

Background: Over the last 30 years, total ankle arthroplasty (TAA) has become a viable surgical option for end-stage ankle arthritis^1,2. The aim of TAA is to relieve pain and preserve ankle joint range of motion, which, by definition, shields adjacent joints^3-6. Alignment is essential for the longevity and survival of TAA, since malalignment of TAA components can cause abnormal loading patterns with subsequent polyethylene wear and early implant failure^7-12. Therefore, patient-specific instrumentation with higher accuracy of tibial and talar component placement and shorter operative times has major advantages in TAA¹³. This present video article describes the use of CT-based patient-specific instrumentation for TAA implantation.

Description: On the basis of preoperative CT scans (PROPHECY Ankle CT Scan Protocol; Wright Medical Technology), a surgical plan is created with comments from an engineer that include the sizing and positioning of TAA implant components (INFINITY with ADAPTIS Technology Total Ankle System; Wright Medical Technology). This plan is reviewed by the surgeon with the opportunity for corrections and adjustments. After approval, the patient-specific cut guides for the TAA are manufactured. TAA with patient-specific cut guides is performed with the patient under general anesthesia, usually with a popliteal and saphenous nerve block for intraoperative and postoperative pain management. The patient is positioned supine with a bump underneath the ipsilateral hip in order to align the foot in neutral rotation. A thigh tourniquet is applied and set at 275 mmHg. Landmarks for the incision are outlined on the skin and the leg is exsanguinated. An anterior approach with a standard central incision is made, creating full-thickness skin flaps medially and laterally. Dissection of the superficial peroneal nerve (SPN) branches should be avoided. The interval between the tibialis anterior tendon and the extensor hallucis longus tendon is entered, and the neurovascular bundle with the deep peroneal nerve (DPN) and the anterior tibial artery is protected and retracted laterally. Hohmann retractors are placed medial and lateral, taking care not to place too much tension on the skin. The anterior distal tibia and the dorsal talus are cleaned of all soft tissues, periosteum, and possible residual cartilage in order to obtain a good cortical read. The patient-specific cut guides (INFINITY PROPHECY, Total Ankle System; Wright Medical Technology) are placed first at the distal tibia and are fixed with temporary pins. Anteroposterior (AP) and lateral fluoroscopic images are made in order to confirm alignment of the tibial alignment guide, which should be neutral relative to the mechanical tibial axis. Once the position is appropriate, the guide is switched to the tibial resection guide, followed by tibial resection with use of an oscillating saw. The patient-specific talar alignment guide is then placed and fixed with pins. Pins are placed through the anterior pin holes, and the guide is switched to the cut guide. AP and lateral fluoroscopic images are made in order to check the talar resection. The talar resection guide will not necessarily be the same size as that used during the tibial resection. A lamina spreader is inserted, and ligament balancing is performed. The posterior capsule can be released at this time if it is tight. Next, the tibial trial is placed over the pins and the appropriate AP positioning of the tibial component is determined and checked on lateral fluoroscopy. Once the position is set, the broaches for the pegs are inserted and tapped in with a mallet. A talar dome trial is inserted together with a polyethylene insert trial, which should engage with the tibial trial. The talar component alignment and rotation are checked clinically as well as under fluoroscopy. Under axial compression and ankle dorsiflexion and plantarflexion, the talar component will rotate into its anatomic position. Two 2.4-mm Steinmann pins are utilized to fix the talar trial component temporarily. The talar resection guide is placed. Temporary fixation screws are placed and tightened by hand. The chamfer cuts are made with an oscillating saw. The talar pilot guide is placed, and the talar reamer is utilized to plunge cut in order to prepare the talar surface. Once this is finished, the pins and the guides are removed, and the residual bone is removed with use of a rongeur. Irrigation is performed with a saline solution. The definitive components are opened, and the tibial component is implanted first and impacted. The tibial pegs must be in the prepared holes. Verification that the component is fully seated is confirmed under lateral fluoroscopic imaging. The talar component is then inserted and impacted. A trial polyethylene liner is inserted, and varus and valgus stress and range of motion are tested. The liner size is then determined. The liner insert guide rail is attached, and the liner is slid into the joint space. With a gentle tap on the liner with the impactor, the fixed-bearing mechanism is locked. Finally, osteophytes, which could block the range of motion, are removed. Final fluoroscopic images are made. After copious irrigation, the wound is closed in layers. Sterile dressings are placed over the wounds, and a padded tri-slab splint is fashioned to immobilize the limb in neutral ankle dorsiflexion.

Alternatives: Nonoperative alternatives include shoe wear modification, the use of NSAIDs, physiotherapy, physical therapy, the use of an orthosis, ankle bracing, and intra-articular injections. Operative alternatives include joint-preserving osteotomies and ankle arthrodesis (AA) (arthroscopic or open).

Rationale: In comparison to ankle arthrodesis, prospective and retrospective cross-sectional studies showed that several patient-reported outcomes were greater after TAA than after AA, without a significant difference in revision rates and complications^14-17. The anterior approach is the most commonly used approach for TAA and gives the surgeon the best exposure of the ankle joint. Varus and valgus deformity of >15° is a relative contraindication, and >20° deformity is an absolute contraindication for TAA¹⁸. If these deformities are not addressed appropriately, long-term survival may be impaired. Multiple studies have shown that malalignment of TAA components can induce high joint contact pressures and therefore lead to early implant failure^7-12. Patient-specific instrumentation in TAA may improve accuracy of implant positioning. Performing TAA using patient-specific cut guides enables the surgeon to plan intra-articular deformity correction, template bone resection, and implant alignment and sizing according to the patient's unique anatomy. Cut guides are based on preoperative CT scans and are single-use instrumentation guides to mark bone cuts for tibial and talar component positioning. Minimal bony resection to preserve the bone stock for future possible revision surgeries is essential, especially in younger patients with end-stage ankle arthritis (< 55 years). Additionally, operative time and fluoroscopy time has been decreased compared with the traditional standard referencing guide technique in TAA¹³. Longer operative times have been shown to place patients at higher risk for wound complications in TAA¹⁹, which could be reduced by performing TAA with patient-specific cut guides.

Expected outcomes: Patients start weight-bearing at 2 weeks postoperatively, which is approximately 4 weeks earlier than patients who undergo ankle arthrodesis¹⁷. Patient expectations are more likely to be met by TAA than by ankle arthrodesis²⁰. Gait analysis has shown that walking speed is faster after TAA compared with ankle arthrodesis. Hindfoot and forefoot sagittal motion is greater following TAA, and gait also more closely resembles the patient's natural gait²¹. Analysis of prospective data showed that in the presence of complex deformity or adjacent joint arthritis, as determined by the Canadian Orthopaedic Foot and Ankle Society (COFAS) classification (COFAS 3 and 4 ankles), patient-reported outcomes were better in patients undergoing TAA compared with ankle arthrodesis. In cases of ankle arthritis without deformity, TAA yielded higher patient-reported outcome measures compared with open ankle arthrodesis. Nevertheless, patients who underwent TAA had a significantly higher rate of additional surgical procedures. TAA patients in general have also been shown to have higher reoperation rates, at around 6% to 7% within a 2-year follow-up window^15,17. Long-term follow-up data on TAA have shown revision rates between 16% and 54%; however, these rates were for older implant designs, and these numbers might not be applicable for the implant utilized in the presently described technique^22,23. The Infinity TAA has shown a revision rate of 3% after a 3-year follow-up study²⁴. Infection rates after primary TAA have ranged from 1.4% to 2.4%²⁵.

Important tips: Patient selection and implant selection are key factors for successful outcome in TAA.It is important to communicate expected outcomes and set patient expectations, as TAA often requires secondary minor operations.The aim of the procedure is to align the implant neutral relative to the mechanical axis of the tibia and to align the foot underneath the ankle joint with the foot progression angle in line with the second ray. In order to achieve this, additional procedures, or even a staged approach, might be required for ligament balancing and foot alignment restoration.There is a surgeon learning curve associated with the implantation of a TAA prosthesis, and adequate training at a high-volume center would be beneficial for early-career foot and ankle surgeons.A perfect fit of the patient-specific cut guides is essential to achieve the planned alignment of the implant. Therefore, a CT scan should be performed within 3 months prior to the surgery, since additional osteophyte development and joint wear over a longer time may result in suboptimal fit of the 3D-printed guides.Meticulous soft-tissue handling is essential to limit the risk of wound complications.Ensure that the medial and lateral gutters are cleared.Ensure that the ankle is balanced. If the gap is asymmetric, meticulously release structures in the concavity of the asymmetry. Potential malleolar osteotomies are required to balance the gap. If the gap is the result of soft-tissue laxity, be sure to reconstruct the incompetent ligaments.If a varus ankle cannot be reduced, be sure to assess the lateral talar process. If it is prominent and represents a block to reduction, resect it.Once the ankle is balanced, assess the sagittal motion. If appropriate rollback or dorsiflexion is not obtained, assess for the presence of a gastrocnemius or soleus contracture with the Silfverskjöld test. Release the contracted tissues as required. For a triceps surae contracture, perform a Hoke procedure. For an isolated gastrocnemius contracture, consider a modified Strayer procedure.Once the ankle prosthesis is in place, assess the position of the foot. If there is a component of cavovarus or planovalgus, address the deformity by additional procedures (i.e. calcaneal osteotomy or midfoot osteotomies).

Acronyms and abbreviations: TAA = total ankle arthroplastyNSAID = nonsteroidal anti-inflammatory drugCT = computed tomographyCOFAS = Canadian Orthopaedic Foot and Ankle SocietyAA = ankle arthrodesisSPN = superficial peroneal nerveDPN = deep peroneal nerveER = extensor retinaculumTA = tibialis anteriorEHL = extensor hallucis longusAP = anteroposteriorDVT = deep vein thrombosis.