The effects of a posterior-stabilized prosthesis on knee ligament loads during walking: a musculoskeletal modelling study

Background The correct balancing of the knee joint ligaments in case of total knee arthroplasty is fundamental for the functional outcome. Hence, it could be of interest for surgeons to understand how the ligaments' tension and intraarticular forces change after the implantation of a knee prosthesis, not only in clinical tests but particularly during functional activities. Many studies have compared the effects of different implant designs but without any reference to changes compared to the natural knee. Methods In this study, a posterior-stabilized prosthesis was virtually implanted in a three-dimensional musculoskeletal model of the knee joint. Through a dynamic simulation of the gait cycle, the knee kinematics, ligaments' tension and tibial-femoral contact force were quantified and compared with those obtained by the intact knee model. Findings In the presence of the prosthesis, the tibia preserved the two peaks of anterior displacement in correspondence with the peaks of knee flexion, even if reduced in relation to the intact knee. The superficial and deep Medial Collateral Ligaments supported the highest load, compensating for the absence of the cruciate ligaments. After the introduction of the prosthesis, the tibial-femoral contact force showed the same trend obtained in the natural knee model, however it appeared reduced compared to the intact knee condition and approached the experimental data recorded by an instrumented prosthesis. Interpretation This study quantified the changes induced by the posterior-stabilized implant in terms of kinematics, ligament tensions and intraarticular forces during walking, demonstrating how musculoskeletal models can support gaining insight into complex biomechanical systems.