Anterior cruciate ligament tears

The anterior cruciate ligament (ACL) works to limit anterior translation and lateral rotation of the tibia with respect to the femur and, together with the posterior cruciate ligament (PCL), accounts for the roll-back mechanism to optimise quadriceps function.

The majority of ACL tears are low energy injuries with 80% being from non-contact. 

The most common mechanism is either pivoting the affected leg, or landing single-legged from jumping.

Biomechanically the knee is close to full extension, the hip is internally rotated and adducted and the body’s centre of mass shifts laterally with respect to the knee. This position combined with a vigorous quadriceps contraction results in overload and failure of the ACL.

The patient will often feel a pop or a tear, have sudden significant pain, will be unable to continue the activity they were involved in and may have a subjective feeling of instability. Knee swelling starts