Real-time soft tissue balance assessment in total knee arthroplasty using a wireless flexible sensor array

Soft tissue balance is crucial for the success of total knee arthroplasty (TKA), influencing joint stability, patient satisfaction, and implant longevity. However, intraoperative assessment of ligament tension is subjective and prone to error. In this study, we present a novel, low-cost, and highly sensitive force measurement system based on flexible sensors for real-time evaluation of soft tissue balance during TKA. The system integrates 24 sensor units (12 each in the medial and lateral compartments) embedded within a custom-designed spacer, enabling continuous real-time force measurements throughout the full knee motion range, including clinically relevant positions: full extension (0°), mid-flexion (45°), and deep flexion (90°). The sensors, fabricated from RTV silicone rubber filled with carbon nanotubes (CNTs) and carbon black, show high sensitivity (0.117 N⁻¹) at low forces and stable performance across a wide detection range (0-100 N). A complete testing platform, including data acquisition circuitry and a graphical user interface (GUI), was developed to visualize pressure distribution during simulated surgery. The proposed system demonstrates rapid response (~ 0.4 s), low hysteresis (~ 1.18%), and high repeatability (CV < 3%) across 2000 loading cycles. These characteristics underscore its potential as a practical intraoperative tool to assist surgeons or robotic systems in optimizing soft tissue balance, thus enhancing TKA outcomes.