Nonlinear analysis of knee kinematic variability after ACL reconstruction for the return to sport.

Abstract

Return to sport (RTS), which is understood as return to the pre-injury level, is the key clinical outcome after an anterior cruciate ligament (ACL) injury. However, the continuum for RTS is complex and multifactorial, and no precise and coherent definition describes this process following the surgical reconstruction of ACL. In fact, after the resumption of sports activities, functional asymmetries are recorded, which show a lower ability of the knee to absorb dynamic forces. This occurs because athletes are complex and nonlinear dynamic systems, adaptive, goal-oriented, and constrained by morphology, physiological, psychological and biomechanical factors, activity and environment, with many interacting parts, all of which are capable of affecting the overall results of the system. By applying the theory of dynamic systems (DTS) to biological systems such as athletes, the importance of variability that is present in human movements is highlighted, which reflects the adaptability of the system to the environment. Kinematic variability analysis of the knee, when used during RTS continuum, provides important information about the changes in neuromuscular function that occur after ACL rupture and reconstruction and can be a valuable approach to analyse joint capacity to provide proprioceptive information and how the entire system processes it. To contribute to a clear and unambiguous definition of return to sport, for the functional evaluation of the knee, this study uses nonlinear analysis tools (inertial sensors) and indicators of nonlinear dynamics (LyE), which can represent a new and more adequate functional measurement of this joint in the evaluation of RTS.