How to Tell if You Tore Your ACL

The knee joint is composed of the femur, patella, and the tibia bones. They are one of the most stressed joints in the entire body and absorb a great deal of stress on a daily basis. In fact, it is estimated that your knees absorb around four times your body weight while walking, running, or jumping. However, your knee joints are not only composed of bones, but also various soft tissue structures such as tendons and ligaments. Unfortunately, because the knee joint is under so much stress and is held together primarily by soft tissues, it is a common location for injury. 

The most common injuries that affect the knee actually affect the soft tissues, specifically the ligaments. There are two main ligaments in the knee known as the Anterior Cruciate Ligament (ACL), which crosses diagonally  below the patella and is responsible for back and forth motion, and the Medial Collateral Ligament (MCL), which is found on the inside of your knee and is responsible for moving your knee sideways. While injuries can certainly affect both of these structures, ACL injuries tend to be more common. 

ACL tears or injuries are generally associated with athletes, specifically those who play sports such as soccer, football, or basketball. However, any sport that involves changing direction rapidly, stopping suddenly, jumping, or accidental collisions can potentially cause an ACL injury. An ACL sprain occurs when the ligament is stretched beyond its normal range of motion and is known as a grade 1 sprain. In a grade 2 sprain, the ligament is said to be partially torn since the excessive stretching causes the ligament to be loose. Finally, grade 3 is known as a complete tear because the ligament has been broken into two pieces. Here are some symptoms you may experience if you’ve torn your ACL: 

Joint Instability

Since the knee joint is primarily held together by ligaments, a tear in your ACL makes your joint unstable. In some cases, the joint may “give out” at the time of the tear, causing you to fall. As a result of joint instability, you may feel like the knee joint is twisting or moving while doing basic activities, like walking. 


In addition to feeling like your knee gave out during a certain activity, you may also hear a popping noise if you’ve torn your ACL. Oftentimes, this popping sound is quite loud and may even be able to be heard by others not directly next to you. In most cases, the popping sound is followed by an immediate shift in the knee. 


Your ACL is surrounded by several blood vessels that supply it with necessary blood flow. Unfortunately, when the ACL is torn, it causes these various blood vessels to rupture. As a result, blood floods into the joint space. This causes the joint to swell, feel hot to the touch, and turn red. 


Of course, feeling pain in the knee joint is a classic sign that something is wrong. In the case of an ACL tear, the pain is caused by the ruptured blood vessels causing swelling in the joint space. The type of pain you experience with an ACL tear can vary, depending on the severity of the damage. Complete ACL tears are generally described as causing an intense pain. 

Decreased Range of Motion

After an ACL tear has occurred, the swelling within the joint will make it very difficult to properly move the joint. Not only will the range of motion in your knee joint decrease significantly, but it will also become difficult to move the lower leg below the knee joint. This, combined with joint instability, makes it exceedingly difficult to walk without the use of a walker, crutchers, or walking stick. 

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