In sports, especially in football, one of the most common knee injuries is the anterior cruciate ligament (ACL) tear, which usually (70%) occurs through non-contact mechanisms that include; sudden deceleration, landing and pivoting manoeuvres which are repeatedly performed. Studies have shown that the incidence of ACL tear in female athletes is two to eight times higher than in men athletes. The research effort to determine the risk factors for sustaining non-contact ACL injuries is increasing as concerns grow about the larger number of incidents, the greater treatment costs and the serious consequences of those injuries.
Mechanically, ACL injury occurs when an excessive tension force is applied on the ACL. A non-contact ACL injury occurs when a person generates great forces or moments at the knee that apply excessive loading on the ACL.
There are number of studies that show that the anterior shear force at the proximal end of the tibia is a major contributor to ACL loading, while there are valgus, varus and internal rotation moments at the knee. According to these ACL loading mechanisms, a small knee flexion angle, a strong quadriceps muscle contraction or a great posterior ground reaction force can increase ACL loading.
The literature also shows that individuals at high risk have a smaller knee flexion angle during athletic tasks than individuals at low risk. Recent biomechanical studies demonstrated that female recreational athletes exhibited small knee flexion angles in running, jumping and cutting tasks. The results of other studies showed that the peak ACL strain occurred at the impact peak vertical ground reaction force shortly after initial contact between the foot and the ground.
The risk factors for non-contact ACL injuries fall into four distinct categories: environmental, anatomic, hormonal and biomechanical.
Recently, a high level of friction between shoes and the playing surface has been identified as a major risk factor for a non-contact ACL injury in the sport of the team handball. In football, there are studies that show that more non-contact ACL injuries occur when the surface is dry. Higher levels of friction between the shoe and the surface are generally associated with better performance but a higher injury risk. That's why we see an increase of ACL tears in areas with artificial grass in football grounds.
There is a need to continue to define specific, neuromuscular, proprioceptive and motor control factors associated with injury. However, until specific predictive and protective factors are identified, training and prevention programmes should continue to be implemented, assessed and improved. There is a pressing need to improve public and participant awareness of the risk of ACL injury and the possibilities for prevention.
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