The effect of change of direction angle on kneeand hip biomechanics : implications foranterior cruciate ligament injury

ACL injuries have been referred to poor mechanics as they frequently occur without contact. Changes in the knee valgus (abduction) angle and knee valgus (external abduction) moment and limb asymmetry have been linked to greater risk of ACLinjury. Change of direction (COD) manoeuvres are important for many field sports, however they are unfortunately associated with non-contact anterior cruciate ligament (ACL) injuries. There is limited literature exploring the associations between lower-limb biomechanical variables during COD manoeuvre associated with ACL injuries. Although players frequently COD at >90° angles, limited knowledge is available on hip and knee joints kinematics and kinetics in term of limb asymmetry and differences between COD at 90° and 135° manoeuvres. In addition, high knee valgus angle and moment during COD manoeuvre is associated with joint positions including increased hip flexion, abduction and internal rotation angles. In addition, isometric hip muscle strength has been reported to predict ACL injuries, indicating that weakness in hip muscles is a modifiable risk factor of the non-contact ACLinjury. However, the relationship between knee valgus angle and moment with hip kinematics and muscle strength during COD at 90° and 135° manoeuvres still unknown. Currently, there has been no published research correlating the hip abductor, extensor, and external rotator strength on frontal plane hip and knee biomechanics during 90° and 135° COD manoeuvres. Therefore, the purposes of this thesis was to (1) determine whether asymmetry in knee and hip biomechanics kinematics and kinetics and hip muscle strength between preferred and nonpreferred limbs during COD manoeuvres at 90° and 135° angles exists, (2)determine whether differences in knee and hip biomechanics kinematics and kinetics between COD manoeuvres at 90° and 135° angles exists and (3) explore the relationships between ACL injury risk factors (knee valgus angle and moment) and hip kinematics and muscles strength during 90° and 135° COD manoeuvres.Three-dimensional (3D) motion analysis technique is a gold stander to assess biomechanical lower-limb during functional activities. In fact, the gold standard for examining lower limb biomechanics is 3D motion analysis system and allows researchers to calculate all three motion planes during dynamic manoeuvres. Inaddition, the isokinetic dynamometer has been considered as a gold standard measurement tool for assessing isometric hip muscle strength and become more popular in sport, research and clinic setting. Healthy male recreational soccer players performed COD manoeuvres at 90° and 135° angles and maximal voluntaryisometric contractions of the hip abductors, extensors, and external rotators. From recorded motion capture, ground reaction force data and hip and knee biomechanics as well as, hip muscles peak torque were calculated. To determine limb asymmetry,a paired sample t-test was conducted using a Holm method correction. Then, pearson’s correlation coefficient (r) was used to explore the relationships between hip kinematics and strength and knee valgus angle and moment. 36 individuals took part in the study (24.25 ±6.21 years, 1.72 ±0.06 m and 66.41 ±10.83 kg). At 135° COD, participants showed greater knee valgus angles at initialcontact and greater peak external knee abduction moments than at 90°. However, no effect of COD angles on knee flexion angle and peak vGRF were found. The results suggest that there were no differences between preferred and non-preferred limbs. Furthermore, the results highlight an important role the hip motion play in controlling kinematic and kinetic risk factors of ACL injury during COD manoeuvres. The findings provided some support that excessive knee valgus angle and moment is potentially associated with poor hip control in all planes. However, there were nosignificant correlation between hip muscles strength and knee frontal plane kinetics and kinematics. It can be concluded that different COD angles demand different hip and knee kinematics and kinetics. The results suggest that sharper COD angle place the knee at more risk for ACL injuries. COD manoeuvres at 90° may be useful for evaluating of individuals but may not be challenging enough to reveal poor neuromuscular control over hip and knee motion. Therefore, sharper angles of examination should be utilized in the evaluation of individuals. Moreover, these results may help provide an appropriate manipulation and intervention on COD manoeuvre to reduce the risk of ACL injury. The findings of this study will increase the knowledge base of ACL injury and can aid in the design of more appropriate neuromuscular and plyometrictraining protocols for injury prevention