If you just injured your knee and have concerns for a fracture, start here first. There are several ligaments in the knee. Here’s a quick guide on what you likely hurt
- Valgus Stress? MCL
- Varus Stress? LCL
- Posterior translation? PCL
- Anterior translation? ACL
- Your rotated your leg with a fixed foot? MPFL
Lets quickly discuss the forces that act on the knee so you understand what the terms from the list above mean
- Translation – the low leg moves forward or backwards against a fixed thigh (anterior/posterior)
- Angulation – the low leg bends in or away from a fixed thigh (varus/valgus)
- Rotation – the foot does not move and the low leg rotates away from the foot
- Axial load – vertical force usually from landing from height
- Direct blow – your knee strikes something
The Inside Of My Knee Hurts. What Did I Sprain?
If you sprained your knee and suffered some valgus stress as depicted above, it is highly likely that you have injured your MCL. A valgus force applies tensile forces to the medial knee as well as compressive forces to the lateral knee. This mechanism occurs when there is force to the outside of the knee. An example is when an offensive lineman falls into one of his fellow lineman.
An additional injury to worry about along the medial knee is an MPFL (medial patellofemoral ligament) sprain. This is a rotational injury and occurs when the foot is stuck in the ground and the rest of the body goes the opposite direction. This ligament is only sprained when the patella (kneecap) gets dislocated. In the event your patella is dislocated, you can pop it back rather easily.
- Push the patella to the middle of the thigh
- Squeeze your quads
The Outside Of My Knee Hurts. What Did I Sprain?
If you sprained your knee and suffered some varus stress as depicted above, it is highly likely that you have injured your LCL. A valgus force applies tensile forces to the lateral knee as well as compressive forces to the medial knee. This is a rather rare mechanism to achieve. The foot is usually fixed to the floor and then force is applied to the inside of the knee
I Hit My Knee On The Dash. What Did I Sprain?
A PCL injury usually occurs when there is posterior translation on the lower leg. This is most common with a direct blow to the front of the knee that forces the low leg to move backwards. This happens most often from a car accident where the knee hits the dash or from diving for a ball and hitting the knee on the ground. The PCL is the strongest ligament in the knee and, as such, is the least often injured.
My Knee Buckled. What Did I Sprain?
If your knee completely buckled or gave out, especially in a non contact setting, you probably damaged your ACL. This is never fun and will always require additional testing and images to confirm but at least you can have some idea before you get there. The forces that cause an ACL injury are anterior translation of the lower leg. However, it is usually caused by a combination of forces (mainly valgus) so the ACL is often injured along with the MCL and meniscus. To learn more about meniscus injuries check here
Now that you have an understanding of the extent of your knee sprain, you can start some early rehab exercises here while you wait to have further testing done with your doctor.