The Terrible Triad – A Major Knee Injury

As a physiotherapist 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 in the knee 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. We have bones, the main thigh bone called the femur has 2 rounded heads that make the top of the knee, and below we have the main shin bone called the tibia which is shaped like 2 cups for the femur to sit on. Slightly below and to the outside of your tibia is the fibula bone but this rarely affects the knee joint and on top we have a patella (knee cap) which floats on top.

Covering the ends of the bones is cartilage, also known as meniscus in the knee. 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 very poor blood supply so when it gets injured it heals very slowly or not at all.

Next we have ligaments which join bones to bones. In the knee we have 4, two crossing over each other inside the knee called the Anterior Cruciate Ligament (ACL) and the Posterior Cruciate Ligament (PCL), and one on each side of the knee called the Medial Collateral Ligament (MCL) and Lateral Collateral Ligament (LCL). Ligaments are there to keep your bones together so they are your balance, they stop you dislocating you knee and are damaged with 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 to the knee the injured player is unable to walk on their leg and will need prehabilitation before surgical repair of the knee and then further rehabilitation afterwards. 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 to get you better, faster but a good knowledge of anatomy helps with understanding your injury.

See our facebook page for a video of a local rugby player, who we are currently treating, being tackled and getting a terrible triad injury!

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