The Terrible Triad – A Major Knee Injury

As physiotherapists, we see a lot of knee injuries. And as far as joints go knees are pretty simple. This is because the knee is a basic hinge joint like you find in a door, and all of the structures have a specific purpose in regards to only two movements – bending or straightening.

So first a little bit of anatomy. Let us start deep and work our way out. The main thigh bone called the femur has 2 rounded heads that make the top of the knee. The bottom part is the main shin bone called the tibia which is shaped like 2 cups for the femur to sit on. To the outside of your tibia is the fibula bone, but this rarely affects the knee joint. And on top, we have a patella (kneecap) which floats with the quads tendons.

Covering the ends of the bones is cartilage, also known in the knee as menisci. On the inside, we call it the medial meniscus and outside is called the lateral meniscus. Cartilage is the padding of the knee and has a very poor blood supply so when it gets injured it heals very slowly or not at all.

Next, we have 4 ligaments which join bones to bones. Two cross over each other inside the knee called the Anterior Cruciate Ligament (ACL) and the Posterior Cruciate Ligament (PCL). One on each side called the Medial Collateral Ligament (MCL) and Lateral Collateral Ligament (LCL). Ligaments are there to keep your bones together. These are your balance to stop you dislocating your knee and are damaged with excessive external force.

Finally we have muscles that move the knee like a hinge. On the front of your thigh are the quadriceps who straighten your knee from a bent position. Behind your thigh are your hamstrings who bend your knee and they are helped by your gastrocnemius (calf) muscle.

So the terrible triad usually occurs when a player has all of their weight on one leg and another player comes from the side and/or slightly in front and takes out the knee. Due to the attachment sites, this snaps the ACL, tears the MCL badly and causes tearing of the medial meniscus. Due to the stability that these 3 structures provide the injured player is unable to walk on their leg. They will need prehabilitation before surgical repair and then further rehabilitation after. With good compliance and good management, a player can be back on the field, fully fit within 9-12 months after surgery.

We see the terrible triad every year and have great prehabilitation and rehabilitation protocols. We can get you better, faster but a good knowledge of anatomy helps with understanding your injury.

Here is a link to our facebook page with a video of a local rugby player, who we fully rehabilitated, being tackled and getting a terrible triad injury!    And click here to see his rehab video.