Novel Surgical Technique for Total Knee Arthroplasty Integrating Kinematic Alignment and Real-Time Elongation of the Ligaments Using the NextAR System

Abstract

This study introduces an innovative surgical approach for total knee arthroplasty (TKA) that combines kinematic alignment (KA) principles with real-time elongation of the knee ligaments through the range of motion, using augmented reality (AR). The novelty of the surgical technique lies in the possibility of enhancing the decision-making process to perform the cut on the tibia as for the KA caliper technique developed by Dr. Stephen Howell. The NextAR is a CT-based AR system that offers the possibility of performing three-dimensional surgical preoperative planning and an accurate execution in the surgical room through single-use infrared sensors, smart glasses, and a control unit. During the preoperative planning, the soft tissue is not considered and only the alignment based on bony reference is ensured. Thanks to the possibility of measuring in real time the elongation of the knee collateral lateral ligaments, the system assists the surgeon in optimizing the cut on the tibia after an accurate resurfacing of the femur as described in the KA surgical technique. The implant used in this novel approach is a medial pivot design (Medacta GMK Sphere) that allows the restoration of the physiological behavior of the software tissue and natural knee kinematics. In conclusion, this novel technique offers a promising approach to TKA, allowing personalized treatment tailored to each patient's unique anatomy and soft tissue characteristics. The integration of KA and real-time soft tissue analysis provided by NextAR enhances surgical precision and outcomes, potentially improving patient satisfaction and functional results.

Keywords: NextAR; augmented reality; enabling technology; kinematic alignment; personalized arthroplasty.

Figure 1

The NextAR System (Medacta International).

Figure 2

Three-dimensional planning: The software enables us to conduct three-dimensional planning based on a CT scan. To preserve the native LDFA, we planned a distal femoral cut at 2.5° valgus with a bone thickness of 6 mm. The posterior femoral cut was set at 0° of rotation with a bone thickness of 5 mm. The tibial cut was planned with a varus of 3.5° and a PTS of 8.5°. Additionally, we determined the optimal component sizes, selecting a femoral component size 3+ and a tibial component size 3. In red is represented the position of the planned femoral component, while in blue is the position of the tibial component.

Figure 3

Camera holder positions: The tibial camera holder is positioned 8 cm below the joint line perpendicular to the joint line, while the femoral camera holder is situated approximately 5 cm above the femoral joint line at a 45° angle; in the image, the top right displays real-time data ensuring that the two cameras, integral to the AR system, maintain contact (in green). It is mandatory to verify that these cameras remain in contact throughout the entire range of motion.

Figure 4

(a) (top) Collateral ligament elongation in extension (top) and in flexion (bottom) showing a shortened MCL before the femoral resurfacing. (b) Collateral ligament elongation after femoral resurfacing shows the restoration of more natural kinematics in extension (top), flexion (bottom), and during the whole range of motion.

Figure 5

Navigation of the distal femoral cut involves aligning the guide with the planned position (indicated by a green line) using real-time position information (indicated by a blue line) in both the coronal and sagittal planes.