Comparison of the contact stress between the sensor and real polyethylene insert in total knee arthroplasty: a finite element analysis

BACKGROUND: In implants, sensors are made of an acrylic-like plastic, while polyethylene (PE) inserts are made of ultra-high-molecular-weight PE (UHMPE). Thus, the stress distribution on the sensor may be different from that on the PE insert due to variations in material properties. The present study sought to analyze and compare the stress distribution profile between the sensor and PE insert after total knee arthroplasty (TKA). METHODS: Finite element analysis was performed to estimate contact stress between the sensor and PE insert after TKA. The materials of the femoral component, sensor, and PE insert were determined as cobalt-chrome-molybdenum, acryl plastic, and UHMWPE, respectively. The stiffness levels of medial and lateral soft tissue were set at 28.8 N/mm and 18.8 N/mm at knee flexion and 24.7 N/mm and 17.2 N/mm at knee extension, respectively. The average and peak contact stress levels on the sensor and PE were analyzed in knee flexion and extension. RESULTS: The average amount of contact stress in the medial compartment was 43.4 MPa on the sensor and 31.9 MPa on the PE insert at knee extension. Meanwhile, the medial compartmental peak contact stress levels were 55.2 MPa on the sensor and 48.8 MPa on the PE insert at knee extension. The other values of average and peak contact stress among the two materials were less than 5 MPa. CONCLUSIONS: There was a difference in the contact stress distribution between the sensor and PE insert due to material properties, especially in the medial compartment at knee extension. The development of a sensor composed of a material with properties similar to a PE insert would be useful in the prediction of femorotibial contact stress in real implants.