The Anterior Cruciate Ligament

By Dr. Adam Roberts, DC, CSCS

What is the anterior cruciate ligament?

The anterior cruciate ligament (ACL) is located within the joint capsule of the knee and offers structural integrity, controlling forward translation of the tibia relative to the femur.

How does the ACL become injured?

Although direct contact can be the mechanism of injury it is most commonly damaged without collision. This injury often occurs through rapid deceleration, explosive change of direction, or landing. The risks are magnified when an athlete performs these movements with compromised body mechanics.

As with other ligaments the ACL injury is broken into categories of sprain:

  • Grade 1 refers to a minor damage to the ligament and although it has been stretched can still support the knee joint.
  • Grade 2 refers to moderate damage to the ligament and laxity at the joint is present.
  • Grade 3 refers to a complete tear of the ligament and is often associated instability at the joint.

Figure 1 - An illustration of a ruptured ACL

What happens following ACL injury?

As the ACL is a substantial ligament when it is sprained there is often a significant amount of pain, inflammation, loss of range of motion at the knee and depending on the grade, laxity or instability.

Injury to the ACL may also be accompanied by damage to the other structures within the knee including other ligaments, the meniscus, and sometimes the bone.

The description of the mechanism of injury, clinical presentation, and magnetic resonance imaging (MRI) is used to diagnose an ACL sprain. The mechanism of injury alone is often very accurate in diagnosis.

ACL injuries are referred to the orthopedic surgeon for consultation and depending on grade surgical intervention may be necessary. Physical therapy is needed in all situations.

How does an athlete reduce his or her chance of injury?

As mentioned previously, direct contact can be the mechanism of injury and this can be tough to avoid in athletic situations. However with the majority of ACL injuries being caused by an athlete's own movement there are things that can be done to minimize your risk.

Strengthening your muscles will help offer support to the knee joint and will create the foundation for solid mechanics and proper movement. It is important to strengthen not just the quadriceps and hamstrings but also the hip and core muscles.

Quality movement patterns should be practiced. Drills designed to develop and rehearse proper body mechanics while accelerating, decelerating, changing directions, jumping and landing are excellent for all athletes.

Maintaining a level of cardiovascular conditioning that prevents fatigue during competition will help reduce mistakes in body mechanics caused by exhaustion.

Proper warm-ups are very useful in preparing the body for athletic movement. A general warm-up such as time on a bike or a light jog should be followed by a dynamic warm-up and also a specific progression of the athletic task to be performed.