The knee joint is comprised of three bones: your thighbone (femur), shinbone (tibia), and kneecap (patella). Your kneecap sits in front of the joint to provide some protection. Bones are connected to other bones by ligaments. There are four primary ligaments in your knee. They act like strong ropes to hold the bones together and keep your knee stable.

One of the most common injuries to the knee is a sprain or tear to the anterior cruciate ligament, commonly known as the ACL. The ACL runs diagonally in the middle of the knee. It prevents the tibia from sliding out in front of the femur, as well as provides rotational stability to the knee.


About half of all injuries to the anterior cruciate ligament occur along with damage to other structures in the knee, such as articular cartilage, meniscus, or other ligaments.

Injured ligaments are considered "sprains" and are graded on a severity scale.

Grade 1: The ligament is mildly damaged in a Grade 1 Sprain. It has been slightly stretched, but is still able to help keep the knee joint stable.

Grade 2: The ligament is stretched to the point where it becomes loose. This is often referred to as a partial tear.

Grade 3: This type of sprain is most commonly referred to as a complete tear of the ligament. The ligament has been split into two pieces and the knee joint is unstable.

Partial tears of the anterior cruciate ligament are rare; most ACL injuries are complete or near complete tears.

While all athletes are susceptible, those who participate in high demand sports like soccer, football, and basketball are more likely to injure their anterior cruciate ligaments. Depending on the extent of the damage and on the recovery process, this could be not only a season-ending but a career-ending injury.

Research has shown there may be several influences on the likelihood of ACL injury, such as the playing surface, playing style, shoe wear, altered neuromuscular control, and deficits in strength. However, you may not be an athlete and still experience an injury to the ACL. There are several anatomical or structural predisposing factors in addition to the aforementioned external factors that increase one’s risk for injury. Some intrinsic factors include a narrow intercondylar notch, generalized joint laxity, malalignment of the legs, and hormonal influences to name a few. In fact, female athletes are 6-8x more likely to suffer an injury to the ACL than male athletes. Yes, you read that right.

Mechanism of Injury

The anterior cruciate ligament can be injured in several ways:


When you injure your anterior cruciate ligament, you might hear a "popping" noise and you may feel your knee give out from under you. Other typical symptoms include:


Most ligament injuries can be diagnosed with a thorough physical examination of the knee. The two most renowned tests for identifying ACL injury are Lachman and Anterior Drawer.

Other imaging which may help your doctor confirm your diagnosis include an X-ray to rule out broken bones and an MRI to assess the soft tissue and ligament damage. However, an MRI is not always necessary to make the diagnosis of a torn ACL.


If you have injured your anterior cruciate ligament, you may require surgery to regain full function of your knee. This will depend on several factors, such as the severity of your injury and your activity level.

Nonsurgical Treatment

While a torn ACL will not heal without surgery, nonsurgical treatment may be effective for those who are elderly or have a low activity level. If the overall stability of the knee is intact, your doctor may recommend nonsurgical options, including bracing and physical therapy.

Surgical Treatment

Most ACL tears cannot be sutured (stitched) back together. To surgically repair the ACL and restore knee stability, the ligament must be reconstructed. Your doctor will replace your torn ligament with a tissue graft. This graft acts as a scaffolding for a new ligament to grow on.

Grafts can be obtained from several sources. Autografts, or self-grafts, are often taken from the patellar tendon, a hamstring tendon, and sometimes, the quadriceps tendon. An ACL graft may also be taken from a cadaver, referred to as an allograft.

There are advantages and disadvantages to all graft sources. You should discuss graft choices with your own orthopedic surgeon to help determine which is best for you.

Because the regrowth takes time, it may be six to nine months or more before an athlete can return to sports after surgery. Typically, return to play follows full range of motion, flexibility to meet demands of the sport, lack of apprehension, and near full strength.


Whether your treatment involves surgery or not, rehabilitation plays a vital role in getting you back to your daily activities. A physical therapy program is crucial in helping you regain knee strength and motion. The general timeline for rehabilitation and return to play are typically surgeon-specific but the goal is ultimately the same: control swelling, restore range of motion and strength, and normalize your walking pattern. In the athletic population it is also essential to regain agility and proprioception to protect the integrity and stability of the joint. With land-based and aquatic-based programs, our licensed therapists will work with you to develop a comprehensive plan of care to help you safely return to the sport or activity you love.


Risk for re-injury or tearing the other ACL increases by 4-6x after initial injury!

We offer free screenings at all of our locations to assess your risk of knee and other orthopedic injuries. Give Aquahab Physical Therapy a call with any questions regarding your prehab or rehab needs - 866.577.3422!


Watch below for exercises to help prevent knee injury - featuring Ali Krieger, USWNT soccer star and ACL/MCL tear survivor.