Anatomy of the Knee

At some point in your athletic career, whether it was football, baseball, soccer, weightlifting or even helping your mom plant flowers, you’ve probably experienced some type of knee pain. Knee pain can be extremely debilitating just like any other injury, but once we begin to learn about the knee and the injury process, we can make better decisions in taking the correct steps on the road to recovery. So before we get into injury specifics, rehabs and such, let’s take a step back and quickly overview the anatomy of the knee joint.

            The knee joint is a modified synovial hinge joint. When we think of a hinge on a door, it helps swing the door in two different directions while staying smooth and controlled. The knee does the same thing, mainly allowing for flexion and extension. There is a little additional rolling and gliding to allow the full range of motion (ROM). The entire knee complex is made up of three articulations, (where bones come together) which include the medial and lateral tibiofemoral joints and the patellofemoral joint. The medial and lateral tibiofemoral joints come together with the medial and lateral femoral condyles articulating with the medial and lateral tibial condyles. The patellofemoral joint articulation is between the posterior aspect of the patella and the patellar groove of the femur, where it allows gliding of the patella for normal ROM.  In terms of the bony anatomy of the knee, the fibula does not play a role, although it does serve as an attachment point for some tendons and ligaments. So for that reason we won’t talk about the tibiofibular joints at this time.

            These articulations are not the most stable because of how the femoral condyles sit in on the tibial plateaus. However, the integrity of the joint is enhanced with the menisci, which sit in between the tibiofemoral articulations, and help deepen the socket, provide shock absorption for the joint, and allow for smooth ROM.

            The static stability of the joint is provided by the extracapsular and intracapsular ligaments, which we will breakdown. The dynamic stability of the knee joint is provided by the numerous muscles and tendons that attach in various locations in and around the knee. The main muscular stability for the anterior knee comes from the quadriceps muscle group, which includes the rectus femoris, vastus lateralis, vastus medialis and vastus intermedius (there is another muscle called the articularis genu, which some consider the fifth quadriceps muscle.. now you can try to stump somebody with that question today!). The posterior stabilization (and main stabilizer for the ACL) of the knee comes from the popliteus and hamstring muscle group which includes the semitendinosus, semitendinosus and biceps femoris. The medial stabilizers of the knee are the adductor group, which includes the adductor magnus, longus and brevis, gracilis and additionally the sartorius. This is not a comprehensive list as some of the adductors are more proximal. Finally, the lateral stabilization mainly stems from the iliotibial band and biceps femoris. Again these are just the muscles that act specifically at the knee joint and we will touch more on specific musculature when talking about injuries and injury rehab.

The extra capsular ligaments include the patellar ligament (tendon), lateral collateral ligament, medial collateral ligament, oblique popliteal ligament and arcuate popliteal ligament. We will focus on the first three. The patellar ligament provides articulation from the tibia to the patella and is continuous with the quadriceps tendon on the superior portion of the patella. The lateral collateral ligament extends from the lateral femur to the fibular head, and this provides resistance against varus forces, or when the knee is shifted or forced laterally. The medial collateral ligament extends from the medial femur to the medial surface of the top of the tibia and this provides resistance against valgus forces, or when the knee is forced inwards (a common problem in ACL injuries). The oblique and arcuate ligaments help provide posterior strength of the knee joint.

The intra-articular ligaments include the anterior and posterior cruciate ligaments (ACL and PCL) and menisci. The ACL is the main stabilizer of anterior translation of the tibia on the femur whereas the PCL resists against posterior translation of the tibia on the femur. The medial meniscus is “C” shaped and the bigger of the two menisci. It spans from the anterior to the posterior intercondylar area of the tibia and meets with the deep fibers of the MCL. The lateral meniscus is much smaller and more round shaped and it spans the lateral tibial intercondylar area.

There are dozens more small ligaments, bursae, retinaculum, blood vessels and nerves that we have not talked about today, and really that would be overkill at this point. I wanted to be able to introduce you into the knee joint and its basic anatomy, setting the base for you to have a better understanding of your body, your performance and your injuries. We will build off of this article in the future when we begin to cover specific injuries, so if you have any questions, comments or concern feel free to reach out and always remember to #HealByMoving.

Todd SabolComment