Ligament Injury Grades

  • Grade I – Slight overstretching of the ligament fibers (fibrils) that causes pain. Only minimal local swelling or bruising noted.
  • Grade II – Partial tearing of the ligament fibers (moderate tear) that typically results in more pain and joint laxity, and involves swelling and bruising.
  • Grade III – Complete tear/rupture of the ligament that causes increased laxity, and often instability, and involves severe initial pain, swelling, and bruising.

Experiencing knee pain? Learn about our physical therapy services for knee pain.

Anterior Cruciate Ligament (ACL)

What is the ACL? The Anterior Cruciate Ligament (ACL) is one of the two main ligaments positioned in the middle of the knee. It runs opposite the Posterior Cruciate Ligament (PCL), stretching diagonally, posterior to anterior, and attaches towards the front of the tibial plateau (shin bone). Its main function is to prevent excessive anterior translation of the tibia on the femur, or too much gliding forward of the shin bone. It also has an important role in limiting rotational forces. The ACL has both a nerve and blood supply, although a portion of the ligament is avascular, which contributes to its poor healing capabilities. The neural innervation of the ACL, and all of the ligaments of the knee, are not just for pain but also play a huge role in proprioception, or our body’s sense of joint position. This is partly why the ACL is so important for balance and stability of the knee. How is the ACL typically injured? Like most ligaments, injuries typically occur when the tissue is overstretched in the motion it is oriented to resist. For the ACL, that means when the tibia slides too far forward on the femur, especially when rotation is involved. This generally occurs when planting the foot into the ground as one attempts to quickly change direction or pivots. Approximately 70% of ACL injuries are non-contact, and are significantly more common in females for various reasons stated in research.


What is the PCL? The posterior cruciate ligament (PCL) runs diagonally opposite of the ACL, crossing its path to make an “X” in the middle of the knee. Unlike the ACL, the PCL restricts excessive posterior translation, or sliding backward of the tibia on the femur. This ligament is nearly twice as thick as the ACL, meaning that it is almost twice as strong. This is why, along with the orientation of the ligament, PCL injuries are less common than ACL injuries. How is the PCL typically injured? The PCL can be injured by “missteps” and poor landing from jumping similar to the ACL. However, the most common mechanism of injury is during motor vehicle accidents. This is typically called the “dashboard injury,” as the ligament can be injured when the tibia slams into the dashboard after a sudden stop or impact, shoving the tibia posteriorly.

Medial Collateral Ligament (MCL)

What is the MCL? The Medial Collateral Ligament (MCL) is a two-part ligament found on the medial (inner) aspect of the knee. The deep part of this ligament attaches to the medial meniscus and the tibial joint line, and the superficial part starts and ends more superficially on the thigh and shin bone. The MCL acts to restrict excessive separation of the inside of the knee joint, something called a valgus force. How is the MCL typically injured? As the MCL is oriented to resist excessive separation of the inside of the knee joint, most injuries occur from impact to the outside of the knee (think of a football player being tackled from the outside leg). This causes excessive stretching to the inside of the knee and can damage the MCL. Because a part of the MCL attaches to the medial meniscus, damage often occurs there as well. Have you, or someone you know, experienced knee pain or injury from a vehicular accident, sport incident, or painful misstep? Contact Life’s Work Physical Therapy to schedule an appointment at one of our Portland locations.

Lateral Collateral Ligament (LCL)

What is the LCL? The Lateral Collateral Ligament (LCL) sits opposite the MCL on the lateral (outer) aspect of the knee. It is strong, but much thinner than the MCL, and resists force coming from the inside of the knee (varus force), which would stretch the outside of the knee joint. It also resists lateral, or external, rotation of the knee joint. How is the LCL typically injured? Injuries to the LCL are less common than the MCL, occurring approximately 25% of the time. The LCL is usually damaged with a sudden varus force or twisting of the knee, such as when attempting to change directions when the foot is planted on the ground. It should be noted that the LCL and MCL are both susceptible to repetitive stress that can cause an overuse injury over time.

The Unhappy Triad

Because of their specific orientation and susceptibility to certain stresses, the ACL, MCL, and meniscus are often all damaged simultaneously in a single event. It used to be thought the medial meniscus was more often injured, versus the lateral meniscus, with ACL tears. This was nicknamed the “unhappy triad,” which also included damage to the MCL. However, research has shown that lateral meniscal tears are more common with ACL tears.

Rehabilitation at Life’s Work Physical Therapy

Much can be done to help guide the healing and rehabilitation of knee ligament injuries. At Life’s Work PT, that process starts with accurate diagnosis stemming from a detailed history taking and evidence-based clinical testing. Our expert team of clinicians are excellent at evaluation and diagnosis of knee injuries, and will help you determine the best course of action towards recovery. If you have injured your knee, contact Life’s Work Physical Therapy today for an hour-long examination.