MCL vs. ACL: What’s the Difference?

When talking with a healthcare provider, medical jargon can quickly become alphabet soup. The knee, for example, houses the anterior cruciate ligament, posterior cruciate ligament, medial collateral ligament and lateral collateral ligament. The ACL, PCL, MCL and LCL respectively. Huh? What do those words and acronyms even mean? What do these structures do for the knee anyway? In the absence of an explanation, this jargon can become confusing or overwhelming for patients. Let’s take a deeper look at two of the major ligaments in the knee and make some sense of the alphabet soup, shall we?

Anatomy of MCL vs. ACL

The ACL, PCL, MCL and LCL are the four major stabilizing ligaments of the tibiofemoral joint, your knee. The first letter of each acronym identifies the location of the ligament and the second letter identifies the type of ligament. The anterior cruciate ligament (ACL) oftentimes is at the forefront of the news about knee injuries, but it’s actually the injury to the medial collateral ligament (MCL) that occurs more frequently. In a systematic review performed in 2019, Kluczynski et al found MCL injuries account for 40.8% of all knee injuries for NFL players compared to only 19% for the ACL.¹

“Medial” as it relates to the MCL, indicates the ligament is located on the inner portion of the knee and “collateral” means on the side. The MCL runs from the medial condyle of the femur (thigh bone) to the tibia (shin bone). Its role is to provide stability through the medial side of the knee and to prevent collapse of the knee inward. The MCL has good blood supply and is located outside of the capsule of the knee joint. This allows for faster healing timetables and often times the absence of need for surgical intervention. On the other hand, the ACL is found inside of the tibiofemoral (knee) joint and runs from the back of the femur to the front of the tibia; the ACL has poor blood supply. “Anterior,” in this case, indicates the ligament attaches the front of the tibia whereas the PCL attaches towards the back. Both the ACL and PCL are cruciate ligaments which means they “cross” within the knee joint. Poor blood supply leads to slower healing time comparatively to the MCL and the need for surgical intervention in most cases. The ACL is crucial in instances like landing from a jump, any start-stop motion and cutting activities.

Injuries and Treatment Options

Generally speaking, injuries to the MCL and/or ACL can be classified using a three-grade system. Grade 1 injuries involve a slight overstretch of a ligament, Grade 2 injuries involve partial tearing of a ligament and Grade 3 injuries involve full thickness tearing of a ligament. MCL injuries occur when excessive stress placed on the knee causes extreme inward collapse (valgus) of the joint, and ACL injuries occur when excessive stress placed on the ACL overcomes the strength of the ligament i.e. hyperextension or shear with rotation of the knee.

Medical management of MCL and ACL injuries vary. For example, most MCL injuries are managed conservatively with the use of physical therapy, whereas ACL injuries more often times require surgical intervention. At times, MCL and ACL injury can occur simultaneously as part of the “unhappy triad.” The unhappy triad occurs when an injury is sustained to the ACL, MCL and meniscus (shock absorbing cartilage within the knee) at the same time.

In Pain? Visit a Physical Therapist

Although the ACL and MCL are very similar, they do have distinct differences and roles within the knee. Both are important stabilizing structures utilized to maintain the structural integrity of the tibiofemoral joint. Are you dealing with knee pain or instability? Visit an Athletico near you where one of our talented rehabilitation professionals help you get back on the path to recovery and to living your life. Request a free assessment today. Free assessments are available in-clinic and virtually through our Telehealth platform.

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The Athletico blog is an educational resource written by Athletico employees. Athletico bloggers are licensed professionals who abide by the code of ethics outlined by their respective professional associations. The content published in blog posts represents the opinion of the individual author based on their expertise and experience. The content provided in this blog is for informational purposes only, does not constitute medical advice and should not be relied on for making personal health decisions.

References
1. Kluczynski MA, Kelly WH, Lashomb WM, Bisson LJ. A Systematic Review of the Orthopaedic Literature Involving National Football League Players. Orthop J Sports Med. 2019;7(8):2325967119864356. Published 2019 Aug 20. doi:10.1177/2325967119864356