Knee Injury Series Part 1: Knee Physiology

If you are a healthy, active individual, there is a high probability that at some point in your life you will have a knee injury. If you play sports that require quick pivots such as basketball, soccer, football, gymnastics, dance, tennis and skiing, you are particularly at risk. While ankle injuries are slightly more prevalent, a knee injury is much more likely to be debilitating. 50% of sports knee injuries will require medical attention and more than 400,000 individuals have full-on knee replacement surgery each year. Ask any sports medicine professional, and they will tell you that knee injuries are the most common reason a player is sidelined for an entire season.

The knee is a remarkable hinge joint between the femur (thigh bone), the tibia (shin bone), fibula (long slender bone next to the tibia) and the patella (knee cap). It has considerable stability thanks to a network of ligaments, cartilage and muscles, but an injury can destabilize the patella, forcing an athlete to wear a patella stabilizer during training. The Q-angle, or the joint area between the tibia and femur, is a portion of the knee that is prone to overuse injury and osteoarthritis.

Critical knee-related muscles include the quadriceps and hamstrings. The quadriceps (quads) are the longest, leanest muscle group in the human body. They connect to the top part of the patella / kneecap and when the quads contract, they pull laterally, extending the leg. Your quads are made up of four muscle groups, the vastus medialis, the vastus lateralis, the vastus intermedius and the rectus femoris. When individuals experience a knee injury in this area, they often lose significant strength in the vastus medialis, located at the lower inside potion of the quad. This muscle is critical to patellar stability, so an effective rehabilitation regimen should pay specific attention to strengthening that area in order to restore knee tracking alignment. Conversely, the hamstring muscle group provides medial knee stability and controls the knee flexion (i.e. bending your leg at the knee.)

When it comes to knee injuries, tendons are particularly at risk. The knee relies on four key tendons for stability, specifically the MCL, LCL, ACL & PCL. The medial collateral ligament (MCL) is part of the medial stabilizers and is located deep within the knee below the knee. It connects to the lateral meniscus, so it is not uncommon to have other injuries, such as a meniscus, ACL or cartilage tear when you injure the MCL. For this reason, many MCL tears are effectively treated with an ACL brace. The anterior cruciate ligament (ACL) connects to the femur to the lateral meniscus. Like the MCL, an ACL injury is frequently accompanied by other ligament or cartilage injuries. The lateral collateral ligament (LCL) runs along the side of the knee, connecting the femur to the tibula. This ligament is not attached to the lateral meniscus, making it less likely to be injured. Lastly, the posterior cruciate ligament (PCL) also connect the femur to the tibia, holding the knee into place and preventing the tibia from moving posterior to the femur.