Causes and Treatment of ACL, MCL, or PCL Knee Injuries

Mature woman in gym holding painful knee

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The ACL (anterior cruciate ligament) and the PCL (posterior cruciate ligament) are the two major ligaments in the knee that work together to provide stability in the knee. They cross each other and form an 'X' which allows the knee to flex and extend without side to side movement. And they are two of the most common serious knee injuries that happen to athletes.


The anterior cruciate ligament (ACL) is one of four major ligaments that provide stability to the knee joint. Injuries to these cruciate ligaments of the knee are typical sprains. The ACL is most often stretched, or torn by a sudden twisting motion while the feet remain planted.

ACL injuries are most common during sports that require a sudden change of direction, sudden, abrupt stops and starts, and lots of jumping such as in football, basketball, and soccer. The most common treatment for a torn ACL is arthroscopic surgery and ACL reconstruction.


ACL injuries, including partial or complete tears, can occur when an athlete changes direction rapidly, twists without moving the feet, slows down abruptly or misses a landing from a jump. This type of movement may cause the ACL to stretch to the point of tearing.

Other things may contribute to ACL injuries; one is gender. Women are two to eight times more likely to suffer from ACL injuries because of genetics. Turns out women's ACLs express 32 genes differently than men's, and three of those expressed genes control specific proteins related to ligament structure and integrity.

PCL injuries are likely with impacts to the front of the knee, or from hyper-extending the knee. The PCL can also be injured by a direct impact from the outside of the knee joint, such as those that occur during soccer or football. Both the ACL and PCL can be injured or torn by a sudden twisting of the knee joint.

Cruciate ligament injuries don't always cause pain, but typically a loud popping sound can be heard at the time of the injury.


The degree of injury may determine the type of treatment recommended. Incomplete ACL and PCL tears are treated conservatively to allow the body to hear on its own. Rest, ice, compression, and elevation are the immediate treatment. Anti-inflammatory medications and NSAIDs can help reduce pain. Physical therapy is often recommended to regain and build muscle strength over time.

For a complete tear of the ACL, arthroscopic surgery and ACL reconstruction is usually performed.

Medial Collateral Ligament Injuries

The medial collateral ligament (MCL) is more easily injured than the lateral collateral ligament (LCL). It is most often caused by a blow to the outer side of the knee (such as occur in contact sports) that stretches and tears the ligament on the inner side of the knee.

The classic sign of this injury is hearing a "pop" and feeling the knee buckle sideways. Pain and swelling are immediate. To diagnose a collateral ligament injury, a medical professional will perform several manual tests (applying pressure on the side of the knee to determine the degree of pain and looseness of the joint) and possibly order an MRI to confirm the diagnosis.

Treatment for Minor Sprains

Minor sprains of the collateral ligaments will heal with rest and gradual return to activity. R.I.C.E., rest, ice, compression, and elevation, help reduce pain and swelling. A knee brace may be used to protect and stabilize the knee. A sprain may take 2 to 4 weeks to heal. A severely sprained or torn collateral ligament may occur along with a torn anterior cruciate ligament, which usually requires repair with arthroscopic surgery.

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Article Sources

  • Johnson JS, Morscher MA, Jones KC, Moen SM, Klonk CJ, Jacquet R, Landis WJ.Gene expression differences between ruptured anterior cruciate ligaments in young male and female subjects. J Bone Joint Surg Am. 2015 Jan 7;97(1):71-9. doi: 10.2106/JBJS.N.00246.