An ACL sprain is a tear of the anterior cruciate ligament in the knee. This may occur from ‘jarring’ or ‘twisting’ your knee, either in a contact or non-contact situation, and either a sporting or non-sporting environment.
The anterior cruciate ligament (ACL) runs diagonally across the knee originating at the back of the femur (thigh bone) and attaches to the front of the tibia (shin bone). It provides support and stability to the knee joint, in particular, it prevents the tibia (shin bone) displacing forwards.
It is often injured during an uncontrolled or unsuspected/unpredictable fast and twisting movement when the foot is in contact with the floor. The foot is planted on the ground, whilst the knee twists inwards.
Such as in ‘missing a step’ or landing heavily. This is more common in the many ‘twisting and turning’ or ‘jumping and landing’ movements in sport. There is often a higher risk of injury in contact but many occur under bodyweight activity only.
The rapid swelling is caused by bleeding within the joint. This is due to ruptured blood vessels around and within the ACL which causes bleeding into the joint cavity. Learn more about ACL sprains.