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ACL Injuries: The Common Causes, Symptoms, and Treatments

If you’re involved in a high-impact sport, you’re likely no stranger to ACL injuries. Anterior cruciate ligament (ACL) sprains or tears are some of the most common knee injuries. About 100,000 to 200,000 instances of ACL injuries occur every year in the United States alone.

They occur when the ligament that connects the femur to the tibia is stretched past its normal range. This can result in a destabilized knee.


They occur when the ligament that connects the femur to the tibia is stretched past its normal range. This can result in a destabilized knee.

ACL injuries are classified through a grading system. They can fall under Grade I, Grade II, or Grade III. Most fall under Grade III while only 10% to 28% are classified as Grade I and Grade II. That means partial tears and sprains are rare. Most cases are complete or near-complete tears.


Grade I – If the ligament is only mildly damaged, the injury is considered a Grade I sprain. When someone sustains a Grade I ACL injury, they only stretched it slightly past its normal position and the tear is microscopic. In this case, the ligament can still help stabilize the knee joint.

Grade II – When someone sustains a Grade II tear, they injure the ACL to a point where the ligament is slightly loosened. A Grade II injury is often referred to as a “partial tear”. At this level, the knee is somewhat supported but it is slightly more unstable.

Grade III – This is the most severe case of an ACL injury. Also known as a “complete tear”, a Grade III occurs when the ligament is fully severed giving way to an extremely unstable knee. As mentioned before, this is the most common type of ACL injury.


ACL injuries are very common in athletes but in rare cases, non-athletes can also sustain an ACL tear. It’s been noted that female athletes sustain this sort of injury more often than their male counterparts possibly due to their anatomy or muscle structure. Regardless of what activity causes an ACL injury, there are a few movements that generally lead to a tear.

Here are some common causes of an ACL injury:

  • A sudden stop or change in direction. These sort of cutting and pivoting motions can sever the ligaments in the knee. Some sports that can lead to this sort of motion in the knee joint are soccer, football, basketball, gymnastics, rugby, and skiing/snowboarding.
  • Hyperextension of the knee. This can occur when one leaps and lands in a way that forces the knee to bend outside of its normal range of motion. Athletes such as volleyball players and gymnasts are especially prone to this type of injury after a messy dismount or misstep.
  • Stress or impact to the outside of the knee or leg. Essentially, the force of a blow to this area of the body can be enough to separate the femur from the tibia and sever the ligaments in the knee. This type of ACL injury is often a result of direct contact sports such as soccer or football.


When the initial ACL injury occurs, you may hear or feel a “pop”. Your knee may immediately buckle underneath you, unable to fully support your weight anymore. But this will depend on what grade the sustained injury is. Here are a few other symptoms you may notice if you have an ACL injury. Your physician will diagnose you based on if you experienced any of the following instances.

  • Knee pain that prevents you from continuing the activity you’re engaged in (this is more likely with a partial tear).
  • A lack of knee pain (this is more likely if the ligament was completely severed).
  • Swelling within an hour to 24 hours after the event of the injury.
  • Extreme bruising due to internal bleeding within the knee joint.


Each ACL injury will require a case by case course of treatment. Your physician will base treatment options around how active you are and how severe the injury is. Grade I and II ACL injuries will typically follow RICE rules at the beginning of treatment: Rest the joint, Ice the injury, Compress the swelling, and Elevate the knee. Injuries in this range may also require anti-inflammatory drugs to calm swelling and manage pain as well as a knee brace to stabilize the area.

A Grade III injury care plan will also include a RICE protocol. Once the swelling recedes, your orthopedic surgeon can surgically reconstruct the ACL. Most of the time they will opt for arthroscopic surgery. This allows the doctor to make a small incision which will result in a quicker recovery and less scarring. One method your doctor might use to reconstruct the ligament is to take an autograft from your patellar tendon or from a large leg muscle. They might also use donor tissue or an allograft or even stem cell therapy.

Whether your injury is a Grade I, II, or III, once the ligament heals, you’ll likely need to enter a rehabilitation program. This will help to stabilize your knee joint, strengthen the surrounding muscle, and prevent any potential future injuries.


Are you on the hunt for timely, top-tier treatment options for your ACL injury? Parker Sports Medicine & Orthopedics is poised to give you a comprehensive look at treatment courses tailored towards your situation. From x-rays to immediate referral for surgery to regenerative medicine, we can help at any stage of your recovery.

Parker Sports Medicine & Orthopedics

7000 W. 9th Avenue Amarillo, TX 79106

Phone: 806.350.BONE | Fax: 806.350.2664