The knee takes a lot stress from the body due to running, squatting, lunging, and jumping. While running and walking a person’s knee can bear loads of three to four times their bodyweight (Anderson and Parr, 2009, p.574). The knee is also subject to a lot of torque forces because of its position between 2 long bones, the femur and the tibia. The anterior cruciate ligament is a critical stabilizing ligament inside the knee joint that is prone to injury.
The knee is made up of the tibiofemoral joint. Within the tibiofemoral joint there are several structures:
Menisci – disks of fibrocartilage that are attached to the superior plateau (top) of the tibia. Within the tibiofemoral joint there are 2 menisci: the medial meniscus and the lateral meniscus. The functions of the menisci include absorption and dissipation of forces, increases knee stability, and improve the congruency of the joint surfaces to evenly distribute the stress across the joint (Anderson and Parr, 2009, p.575).
Anterior Cruciate Ligament (ACL) – a stabilizer in the knee that prevents anterior translation (forward movement) of the tibia while the femur is stationary, posterior translation (backward movement) of the femur on a stationary tibia, internal and external rotation (twisting) of the tibia on the femur, and hyperextension of the tibia. The ACL is frequently injured during deceleration movements such as changing directions, planting, and cutting (Anderson and Parr, 2009, p.579).
Posterior Cruciate Ligament (PCL) – the primary stabilizer that is shorter and stronger than the ACL. The PCL prevents posterior displacement (backward movement) of the tibia on a stationary femur (Anderson and Parr, 2009, p.580).
Medial Collateral Ligament (MCL) – a ligament that runs across the medial (inside) aspect of the knee to prevent valgus forces (forces hitting the knee from outside). The MCL is more commonly injured over the LCL.
Lateral Collateral Ligament (LCL) – a ligament that runs across the lateral (outside) aspect of the knee to prevent varus forces (forces hitting the knee from the inside).
Types of ACL Sprains
A sprain is an injury to a ligament in the body where a strain is an injury to a muscle. When classifying an ACL sprain, there are three different degrees (Anderson and Parr, 2009, p.142):
First Degree – few fibers of the ligament are torn. The muscles around the injury only have mild weakness with no spasm. There is mild swelling around the joint with a minor loss of function. Typically first degree sprains are described like a “tweak” to the knee and the person is able to “walk it off”. First degree sprains can typically be treated with RICE: Rest, ice, compression, and elevation. The general rule of thumb is if you have pain with a certain movement after a first degree sprain then do not do it until the pain subsides. General strengthening of the knee and the hips will help the patient from re-injuring the ACL.
Second Degree – nearly half of the fibers in the ligament are torn. The muscles around the joint have mild to moderate weakness and may have some minor spasms. There is moderate to severe loss of function at the knee. The injured person may not want to move the knee or put pressure on the injured leg. Moderate swelling will occur around the joint. Crutches may be needed so the person can move around without pain in the knee. A second degree sprain warrants a visit to the doctor to discuss the options for the best outcome for you. Some second degree sprains can heal without surgery depending on what type of activities the injured person would like to return to. If the doctor and the patient choose to forgo surgery then the patient will typically undergo several weeks of physical therapy. Although some second degree sprains will be surgically repaired if the injured person would like to return to high levels of activity such as competitive sports with lots of running and cutting.
Third Degree – the ligament is completely ruptured. The muscles around the joint have mild to moderate weakness and may have some minor spasms. Moderate to severe swelling will occur around the joint. The knee is very unstable and the patient will report the knee is “giving out” especially if the person is turning around a corner or trying to change directions while walking. Other structures in the knee can be damaged in the knee with a third degree ACL sprain such as the MCL and/or the medial meniscus. Popping and cracking may occur within the joint after the injury. The patient should schedule an appointment with a doctor to get the knee evaluated and to see if any other structures in the knee are damaged. Once the doctor has come up with a definitive diagnosis of what structures are damaged, he/she will decide the type of surgical procedure that would be most beneficial for the patient. Third degree ACL sprains can be treated without surgery but the patient will have to make decisions about the types of activities he/she will and will not participate in. Non-surgical treatment of third degree ACL sprains typically have complications such as patellar tendonitis, arthritis, and chronic pain/swelling and are not the preferred treatment but the patient and the doctor will need to make the treatment decision together.
As with any sprain, the patient should use the RICE method as mentioned above. Rest the joint as much as possible. Crutches may be needed to increase the amount of rest at the joint. Ice the area at least once a day after activities that are difficult or painful. Ice the knee for 20 minutes at a time with at least 60 minutes between icing sessions. If the patient is functional enough to perform physical activity without pain, do not ice before activity. Save the ice until after the activity is over.
Compress the joint with an ACE wrap bandage to push out any swelling in the joint. When applying a compression wrap to the knee, start at the calf and wrap upward toward the hip. Use about 75% stretch on the compression bandage. To find 75% stretch, take the bandage and pull the bandage as tight as possible then release the bandage until the bandage is 75% of the length it was when it was pulled as tight as possible. Try to use this amount of tension when wrapping the entire joint. Be sure not to wrap too tight; do not let any numbness occur around the wrap or in the calf and feet. Elevate the joint to help relieve pressure on the joint and to reduce swelling. When elevating the knee, it should be above the level of the heart so any excess fluid will be pulled back into circulation.
Women are more likely to injure the ACL than men (Anderson and Parr, 2009, p.593). Prophylactic (preventative) bracing has not been shown to prevent ACL injuries (Anderson and Parr, 2009, p.594). Improving strength and correcting imbalances between the hamstring and quadriceps muscles can help protect the knee from injuries. Hip strengthening of the gluteus maximus and the gluteus medius can increase stability up the kinetic chain to reduce forces at the knee. If you have any concerns about pain or problems in your knee, contact a doctor, physical therapist, athletic trainer or another qualified health care professional.
Anderson, M., & Parr, G. (2009). Shoulder Conditions. In Foundations of athletic training: Prevention, assessment, and management (4th ed.). Philadelphia, PA: Wolters Kluwer Health/Lippincott Williams & Wilkins.
Note: This article is intended purely for educational purposes. It is not intended to diagnose, treat, or replace advice from a qualified healthcare professional. Every person with an injury is different and needs an evaluation by a physician, physical therapist, athletic trainer, or qualified healthcare professional to identify any problems. Please consult a qualified healthcare professional if you are experiencing any of the signs and/or symptoms described.