Fight Medicine: Ask the Fight Doctor Mailbag

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You had a great post on ACL rehab in May, but what rehab would you suggest for the lesser-reported PCL injury or over-extension of the knee? -- Joy S.

The Fight Doctor: You are right to say the posterior-cruciate ligament is not discussed as much because it is injured far less than the anterior-cruciate ligament. Nevertheless, it can be strained, partially torn or completely ruptured, especially in MMA, where shooting for a takedown can drive the tibia or shinbone backwards, stressing the PCL.

This can also happen in a high-speed motor vehicle accident and is often called a “dashboard” injury because the tibia hits the dashboard and is driven backwards. Since the PCL is in the back of the knee, when the knee is hyperextended, it can stress the ligament as it becomes tight in extension. As you can surmise from the description of the PCL’s injury pattern, its main job is to prevent the tibia from moving backward relative to the femur or thighbone. It also sits behind the ACL, hence the name “posterior.” When the PCL is injured, you want to strengthen the muscles that help prevent the tibia from moving backwards. The biggest muscle group that does this is the quadriceps.

A group of four muscles forms the quadriceps, runs over the front of the thigh and then forms a tendon that runs over the kneecap and inserts near the top of the tibia. The main job of those muscles is to extend or straighten the knee. By their action, they also pull forward on the tibia. If the ACL is intact, it helps limit how much they pull, keeping the knee like a hinge. If the PCL is injured, the quadriceps can contract and help the tibia from being pushed backwards during movement.

The way to help train these muscles to do this is to perform plyometric exercises such as box jumps, which train the body to trigger the quadriceps as soon as the knee sees a stress. Leg presses also help with quadriceps strength, as do leg extension machines, which isolate them even more.

If you do suffer an incomplete PCL injury, you should be examined by a doctor; you may need a knee brace to help stabilize the knee while you rest, allowing it to heal. The same holds true for surgery, but once you are cleared for strengthening exercises, make sure to focus on the quadriceps. As always, stay safe and train smart.

Want your question answered by The Fight Doctor? You can contact him by email at fightmedicine@sherdog.com or find him on Twitter @fightmedicine. You can also read more about MMA injuries at FightMedicine.net.