The Lexicon of Ligaments: Understanding Knee Injuries

PCL…Public Limited Company? Printer Control Language? Python Coding Layer?

MCL and LCL? These are Roman numerals…right?

If—like me--you’re not in the field of orthopedics, you might wonder what these abbreviations stand for. I was familiar with the letters ACL in relation to knee injuries, but only because ACL sprains and tears are so common, especially in athletes.

So what do all these baffling letters mean in medicine?

• ACL= Anterior Cruciate Ligament: The ACL runs diagonally down the front of the knee. The ACL prevents the tibia (shinbone) from sliding out in front of the femur (thighbone) and provide stability in the knee when the body is rotating. People with visible scars running vertically down the front of their kneecaps might have had surgery to repair an ACL tear.
• PCL= Posterior Cruciate Ligament: The PCL runs vertically down the back of the knee. It prevents the tibia (shinbone) from sliding out behind the femur (thighbone). Injuring your PCL requires a powerful force, like the impact of hitting your bent knee against your dashboard in a car accident.
• MCL = Medial Collateral Ligament: The MCL runs along the inside of the knee. Its function is to prevent the leg from extending too far inward. Direct contact from a kick or other impact to the outside of the knee can push the knee sideways, putting pressure on the MCL on the inside of the knee.
• LCL = Lateral Collateral Ligament: The LCL runs along the outside of the knee. Its function is to prevent the leg from extending too far outward. Severe impacts to the inside of the knee can strain the LCL, causing the ligament to tear.

There are a ton of ways in which a person could injure the ACL. ACL sprains are common in a wide range of sports activities, and the characteristic loud pop, sudden instability, and immediate swelling are telltale signs that you’ve seriously injured your ACL.

MCL injuries are nearly as common as ACL injuries, and make up large percentage of knee injuries in contact sports like hockey or American football. Orthopedic surgeons categorize MCL injuries in three grades:

• Grade 1 — Minor injury with minimally torn ligament fibers. Some tenderness and minor pain.
• Grade 2 — Moderate injury with a partial tear. Noticeable looseness in the knee when moved by hand accompanied by major pain, tenderness, and sometimes swelling at the inside of the knee.
• Grade 3 — Severe injury with complete tear. Considerable pain and tenderness at the inside of the knee; some swelling and marked joint instability. This severity of injury is frequently accompanied by a tear of the ACL.

To diagnose the severity of the injury, evaluation by an orthopedic specialist is necessary, often in conjunction with MRI. Because it creates a clear picture of the soft tissues in the knee, MRI has an accuracy rate of nearly 90 percent in determining whether and how badly a medial collateral ligament is torn.

LCL injuries are categorized by similar gradations. They are less common than MCL injuries, and they also do not heal as well. While MCL injuries rarely require surgery, severe LCL tears may require surgery followed by physical rehabilitation.

LCL tears rarely occur in isolation; they usually happen in conjunction with another knee injury. Unlike most knee ligament tears, which occur frequently during high-impact sports, isolated LCL tears ironically sometimes result from the attempt to achieve certain seated yoga poses such as the full lotus or Eka Pada Sirasana (in which the foot is placed behind the head).

Even if you’re not an aspiring yogi or a rugby player, mild to moderate knee injuries are quite common, and it can be helpful to know which ligaments are where.