Robot-Assisted Navigation for Infinity Total Ankle Arthroplasty: Technique Tip

1. INTRODUCTION

End-stage ankle osteoarthritis (OA) severely impacts patients' quality of life. With the introduction of fourth-generation prostheses such as the Infinity total ankle system (Stryker, Kalamazoo, MI, USA), total ankle arthroplasty (TAA) has increasingly become a viable alternative to arthrodesis because it preserves joint mobility.¹ However, the long-term survivorship of TAA is highly dependent on the precision of implant positioning. Biomechanical studies indicate that a coronal alignment deviation of the tibial component exceeding 3° to 5° increases edge loading. This abnormal loading accelerates polyethylene liner wear and can lead to early implant loosening.² Currently, the standard surgical technique for the Infinity system primarily relies on an extramedullary alignment guide. While this instrumentation is well-designed, adjusting the position of the guide still requires the surgeon to visually estimate anatomical landmarks and use repeated C-arm fluoroscopy. Previous studies have reported that the average fluoroscopy time with conventional techniques can reach 77 seconds.³ Despite this extensive intraoperative imaging, approximately 10% to 15% of patients still experience coronal alignment deviations greater than 3°.⁴ Excessive reliance on fluoroscopy not only extends surgical duration but also risks sterile field contamination via repetitive C-arm positioning—both of which are recognized drivers of wound complications, the most common adverse events in TAA.^5,6

To improve surgical accuracy, minimize wound complications, and reduce radiation exposure, patient-specific instrumentation (PSI) has been widely applied. Nevertheless, the clinical application of PSI is limited by long manufacturing cycles, high costs.⁷ In contrast, robotic-assisted surgery systems offer real-time navigation and rigid execution. These systems have already demonstrated clear clinical benefits in hip and knee procedures.⁸ This technical note details the surgical workflow for performing an Infinity TAA assisted by the TiRobot system (TINAVI Medical Technologies, Beijing, China), and evaluates the utility of this robotic approach in simplifying alignment assessment, decreasing wound complications, reducing radiation exposure, and improving overall implant precision.

2. MATERIAL AND METHODS

2.2 Surgical technique

STEP 1: Tracker Installation and Registration

Following sterile prep, a 2.0-mm K-wire secures the patient tracker via an anteromedial proximal tibia stab incision. An intraoperative O-arm 3D scan transmits to the console, achieving automatic registration and eliminating manual point-matching [Figure 1].

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Figure 1: (A-B) Placement of a K-wire in the medial proximal tibia and attachment of the patient tracker. (C-D) Intraoperative O-arm scan of the ankle joint, demonstrating continuous visualization of the robotic arm tracker.

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Step 2: Trajectory Planning

Trajectory planning for the 2.4-mm pins, which will secure the Infinity tibial guide, is performed on the 3D imaging interface of the console. In the coronal plane, the pin trajectory is configured strictly perpendicular to the tibial mechanical axis to accommodate the anatomical design of the prosthesis. In the sagittal plane, the trajectory remains perpendicular to the tibial axis, and the optimal pin height is established, typically approximately 6 cm proximal to the ankle joint line. In the axial plane, at a joint level where the medial malleolus, lateral malleolus, and talus are simultaneously visualized, the trajectory is centered within the ankle mortise to prevent pin malrotation. The continuous review of the 3D spatial data on the console enables direct visual confirmation of the pin positioning [Figure 2].

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Figure 2: (A-D) Trajectory planning for the guide pin in the axial, sagittal, and coronal planes on the console using the acquired 3D scan data. (E) Conventional measurement and positioning of the guide pin using the standard “Spider” jig in the Infinity system, typically located approximately 6 cm proximal to the ankle joint line.

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Step 3: Robotic Execution and Guide Pin Placement

Upon final confirmation of the trajectory planning, the robotic arm is activated. It automatically navigates to and securely locks onto the designated axis. A 2.4-mm pin is advanced through the guide sleeve, serving as a reference to mount the tibial alignment device for the second pin. Robotic control eliminates freehand micro-deviations, and the surgeon avoids initial fluoroscopy radiation exposure in Steps 1 through 3 [Figure 3].

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Figure 3: (A-B) The robotic arm navigates to the planned trajectory and locks into position for guide pin placement. (C-D) Following the mounting of the tibial alignment device, percutaneous fluoroscopic confirmation of the guide position is obtained, and the second pin is inserted (alternatively, both pins can be placed sequentially using the robotic system)

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Step 4: Osteotomy and Implantation

The robotic arm is subsequently retracted. With the critical alignment phase concluded, the limb is exsanguinated and the pneumatic tourniquet is inflated, initiating the open phase of the procedure. Given that the pin trajectory has been rigidly established by the robotic system, the surgeon is only required to adjust the proximal-distal and medial-lateral positioning of the guide under intraoperative fluoroscopic control. The remainder of the procedure proceeds according to the standard Infinity protocol [Figure 4].

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Figure 4: (A-C) Surgical exposure and debridement of the ankle joint, followed by the mounting of the cutting guide and fluoroscopic confirmation. (D-G) Application of the tibial and talar cutting guides to perform the osteotomies, (H-K) and insertion of trial components for assessment, concluding with the implantation of the definitive Infinity tibial and talar components. Notably, a total of only 28 fluoroscopic shots were required for the entire procedure.

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3. RESULTS

We reviewed 113 total ankle replacement cases for this study. The group included 42 robotic-assisted surgeries and 71 traditional surgeries. The robotic approach showed clear clinical data. The surgical team finished the robotic procedures in an average of 75.4±10.2 mins. The tourniquet stayed on for 60.5 ±8.5 mins. The need for intraoperative fluoroscopy dropped significantly. Surgeons took an average of 28.2± 3.4 shots during each surgery. The total intraoperative fluoroscopy time was only 32 seconds. This cut the total radiation dose by about half compared to traditional methods. Patient recovery went well. Only two patients in the robotic group had a minor delay in wound healing. This represents a 5% complication rate. Both wounds healed normally with basic dressing changes.

4. DISCUSSION

The average surgery time in our study was much shorter than traditional times reported in previous studies.³ The robotic system does add time for setup and registration. However, it improves overall efficiency by cutting out repeated intraoperative fluoroscopy checks and guide adjustments during the operation. More importantly, the tourniquet time dropped significantly to an average of only 60.5 ± 8.5 mins. The surgical team also took fewer intraoperative fluoroscopy shots during the procedure. The total intraoperative fluoroscopy time was only 32 seconds. This method cuts the radiation dose by about half.³ Traditional surgeries often rely heavily on frequent intraoperative fluoroscopy checks. Moving the C-arm repeatedly can easily bring germs into the sterile surgical area. A shorter tourniquet time protects soft tissues from poor blood flow. It also limits how long the wound stays open and lowers the risk of infection. Only two patients (5%) in our group had a minor delay in wound healing. Both wounds healed well with basic dressing changes. This complication rate compares very well to the higher rates often seen with traditional methods.6 The robotic system helps newer surgeons greatly reduce the risks of poor tissue blood flow and wound contamination. We must still consider one important trade-off. The robot keeps the surgeon completely safe from intraoperative fluoroscopys, but the patient still receives a specific dose of radiation from the 3D scan.

Our current study focuses mainly on the robotic surgical technique itself. We did not further test the exact accuracy of the implant placement here. In theory, the clear 3D screen helps younger doctors learn joint replacement faster.8 The system stops small hand mistakes and makes the entire surgery much safer and more predictable. We definitely still need long-term data to prove the final clinical results. Future studies must track these patients for many years. We need to know if better early bone alignment actually makes the implant last longer. A surgical robot does cost a lot of money upfront. However, large hospitals can earn that money back over time by sharing the machine across different surgical departments.

5. LIMITATIONS

Our study has a few clear limitations. This is a retrospective review from a single center. We did not randomly assign patients to the robotic or traditional groups. The study also focuses mainly on the surgical steps and early operating room data. We did not use postoperative X-rays or CT scans to prove the exact accuracy of the implant placement. We also lack long-term follow-up data. We do not yet know if the robotic method changes the actual implant survival rate compared to traditional techniques over time. The robotic system also requires an O-arm scan. This scan keeps the surgeon completely safe from radiation, but it still gives the patient a specific dose of radiation. Future studies should use randomized groups, measure the final bone alignment carefully, and track patients for a much longer time.

6. CONCLUSION

Robotic navigation-assisted Infinity total ankle arthroplasty is a safe, precise, and efficient surgical technique. Compared with conventional methods, it streamlines the intraoperative alignment assessment, significantly reduces radiation exposure, and decreases both overall operative and tourniquet times. These advantages effectively mitigate the risks of wound complications and postoperative joint infections. While meriting wider clinical adoption, long-term comparative studies are warranted to determine if these early radiographic advantages translate into improved survivorship and reduced clinical complication rates.