Biomechanics of planned and unplanned change of direction in subjects with and without anterior cruciate ligament reconstruction: a case study

Abstract

Anterior cruciate ligament (ACL) rupture is one of the most recurrent knee injuries in soccer players [1]. Commonly, global performance measures like jumping/hopping distance or time to perform agility test and side-cutting manoeuvres are used as criteria to determine readiness to return to sport after ACL reconstruction (ACLR) [1]. However, athletes may pass these criteria despite ongoing biomechanical deficits while performing the tests. Although ACL injury commonly occurs during change of direction (COD) [2], little is known about how athletes execute COD after ACLR and how they compare to healthy athletes. Also, few studies have investigated the influence of planned Vs unplanned COD on biomechanical parameters related to ACL injury risk. The aim of this preliminary study is to contribute filling this gap, quantifying a set of relevant biomechanical parameters in a healthy and ACLR soccer players during both planned and unplanned COD. Two male soccer athletes (Tegner Activity Score ≥ 6) participated in the study, one healthy (HS) and one with ACLR (12 months before the test; injured limb: left). They performed three maximal 90° planned (COD-P) and unplanned (COD-U) CODs after standardized warm-up. For the COD-U, speed gates (Microgate, WittySem) were used to indicate the COD direction, which was selected randomly. Ground reaction forces (GRFs) of the foot performing the COD were measured by two force plates (AMTI, 1000 Hz). The start line was 5 meters from the force plates [1] and full foot contact with the force plates had to be made for a valid trial. The 3D trajectories of 52 markers located according to [3] were simultaneously measured by an optoelectronic system (Vicon, 200 Hz). Foot-force plates contacts were identified setting a threshold of 20 N on the vertical GRF (vGRF) [1]. A set of ACL injury risk-related parameters were then extracted from GRFs and marker trajectories [4]: ground contact time (GC time ), knee flexion and knee valgus angles at initial contact (KflexIC, KvalgIC), peak vGRF (vGRF peak ), GRF impulse (J), and peak knee abduction moment (KMabd peak ). Mean and standard deviation values over the three trials were calculated for each parameter and each COD type. The value of each estimated parameter is reported in Table 1. In COD-U, ACLR subject showed - 774% KvalgIC and +123% KMabdpeak in the injured/non-dominant limb compared to the dominant, while smaller asymmetry was reported in HS (non-dominant vs dominant: -440% and +93%, respectively). Overall, COD-P has lower asymmetry percentages than COD-U. The results of this preliminary study suggest that different strategies were implemented by the two subjects in both COD-U and COD-P. As expected, due to the small sample size, a clear trend in terms of between-limb and COD type comparison can be hardly identified. The results about the knee kinematics suggest that a higher degree of asymmetry exists in the ACLR subject with respect to HS. A similar consideration can be drawn for kinetic results, where greater knee abduction moment and force impulse are displayed for the injured limb in the ACLR subject. The implemented methodology proved to be robust and can be applied to a larger sample size to strengthen the present results.