ACL Tear – Definition, Anatomy and Causes (Video)

An ACL tear is used to describe any injury to the Anterior Cruciate Ligament.  Most commonly,  the ACL pulls away from its origin on the end of the thighbone.  It may also simply stretch or only be “partially” injured.

The following  video shows the surgical (arthroscopic) appearance of an intact ACL followed by an ACL that has torn from its origin.

ACL tears are one of the most frequently talked about sports injuries. They are one of the most common knee injuries. It is estimated that about 200,000 occur in the US each year.  As sports become more competitive in adolescent and female athletes,  these groups have seen an increase in ACL tear frequency.  In fact, ACL tears are approximately 3 times more frequent in females and about 5% of year-round female soccer and basketball players will sustain an ACL tear.

ACL Anatomy

ACL Tear

Knee Anatomy

Ligaments are thick firm bands of tissue that connect one bone to another.  The ACL is one of the four major ligaments in the knee.  The ACL and the three others (PCL, MCL, LCL),  connect the bottom of the thigh bone (femur) and the top of the shin bone (tibia).  By doing so, these ligaments stabilize the knee.  The ACL is primarily responsible for preventing excessive back to front motion of the tibia on the femur and rotation of the tibia outwards.  When there is an ACL tear, the ACL is unable to prevent these motions and the knee will often feel unstable. This instability will typically be felt during pivoting, cutting and jumping activities.  Some, however,  may have instability with everyday non-sport activities.

ACL Tear Causes

Most often an ACL tear will occur during a non-contact pivoting or jumping activity, such as during skiing, team sports or racquet sports.  Often the injury will occur while engaging in an activity that has frequently been performed in the past without injury.

The following video shows Derrick Rose tearing his left ACL while pivoting (the injury occurs at 0:05 secs. and then again in slow motion at 0:48 secs.).

The following video shows a gymnast tearing his right ACL when landing after jumping (the injury occurs at 1:13).

Occasionally an ACL tear will occur from direct contact to the knee.  ACL tears caused by contact are often associated with additional ligament injuries.  Even more rarely, an ACL tear may occur from a simple slip or fall while performing everyday non-sport activities, such as those that may occur when stumbling on a wet surface or while dancing.

There are a number of potential risk factors for ACL tears.  Those often discussed are:  fatigue, activity intensity (game vs. practice),  field surface,  shoe type,  jumping and landing techniques, size and shape of particular areas of the knee, female sex and associated female hormonal status.

Look for future posts about ACL Tears in which the symptoms, treatment options, prognosis and preventative strategies will be discussed. You may also wish to view the main Orthopaedic Organization’s (AAOS) recommendations in regard to ACL tears.



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