Biomechanical research on effects of joint line height on stress of medial and lateral compartment after unicompartmental knee arthroplasty

Abstract

Objective To investigate biomechanical effects of different joint line height on unicompartmental knee arthroplasty (UKA) and to provide biomechanical evidence for surgical decision during UKA using finite element analysis (FEA). Methods On the basis of knee joint CT data from a healthy volunteer (male, 30 years old, 165 cm and 60 kg) and UKA prosthesis 3D scanned data, the 3D models of normal knee and UKA were constructed. Subject-specific finite element models with inhomogeneous material property assignment were constructed for normal knee and UKA with 3 different height of joint line (-3 mm, 0 mm and +3 mm). Starting from the tibial articular surface, 5 sections were extracted with 2 mm interval. 30 nodes were selected in medial and lateral area, respectively on each section. The mean stress value of nodes was defined as the stress level of subchondral bone. Results Mean values of stress on polyethylene upper surface of 0, -3 and+3 mm joint line position were 14.84, 26.81 and 20.86 MPa, and the difference was statistical significant (t0vs-3=4.896, P0vs-3=0.000; t0vs+3=3.455, P0v+3=0.008; t-3vs+3=2.579, P-3vs+3=0.020). Mean values of stress on tibial prosthesis upper surface of 0, -3 and +3 mm joint line position were 29.69, 50.49 and 39.99 MPa, respectively, and the difference was statistical significant(t0vs-3=5.675, P0vs-3=0.000; t0vs+3=4.755, P0v+3=0.001; t-3vs+3=4.783, P-3vs+3=0.000). When joint line was in 0 mm height, stress level of subchondral bone was similar to that of normal knee. When joint line was in -3 mm height, significantly increased stress was found on polyethylene (increased 81%) and tibial component (increased 70%) surface compared with that of 0 mm height, while stress on trabecular bone under lateral tibial articular surface also increased by 8.7%. When joint line was in +3 mm height, increased stress on polyethylene (increased 41%) and tibial component (increased by 35%) surface were less than that of -3 mm height. Stress on trabecular bone under lateral articular surface decreased by 55.6% compared with 0 mm height. Conclusion During UKA, ensuring a normal height of joint line is benefit to keep the stress path of the medial and lateral tibia similar with normal knee and decrease the risk of premature polyethylene wear, tibial component subsidence and periprosthetic fracture. Key words: Osteoarthritis, knee; Arthroplasty, replacement, knee; Finite element analysis