By Elizabeth A. Murray, Mount St. Joseph University
The knee is a hinge joint between the medial and lateral condyles of the femur and the medial and lateral condyles of the tibia. It must be remembered that the fibula doesn’t directly articulate with the femur, though the patella does. Nevertheless, the patella and fibula are still both crucial elements of the knee joint.
Tibial/Medial Collateral Ligaments
Since the knee is a hinge joint, one can easily guess what kind of ligaments are found on either side of the knee. Yes, collateral ligaments. The tibial collateral ligament, referred to by most as the medial collateral ligament, or MCL, is a relatively wide and flat ligament that connects the medial epicondyle of the femur to the medial condyle and proximal shaft of the tibia.
It’s considered an intrinsic ligament because it blends with the capsule of the knee joint—remember, the capsule is a connective tissue sleeve that covers many synovial joints.
Fibular/Lateral Collateral Ligament
The fibular collateral ligament, commonly known as the lateral collateral ligament, or LCL, connects the lateral epicondyle of the femur to the head of the fibula.
It is much more cord-like and more mobile than the medial collateral ligament, and is an extrinsic ligament, given that it is not connected to the joint capsule.
Menisci of the Knee
The so-called tibial plateau is not exactly flat, since between the medial and lateral condyles of the tibia is a projection known as the intercondylar eminence. On either side of this intercondylar eminence sit the menisci of the knee. These fibrocartilaginous pads are articular discs, but they are usually called menisci at the knee.
The medial meniscus is more C-shaped when seen from above, while the lateral meniscus is more O-shaped. The menisci sit atop the articular cartilage of the tibia and are connected to the tibia at their edges by small attachments known as coronary ligaments.
Each meniscus functions to slightly deepen its articular surface on the tibia; the menisci act almost like cupholders for the rounded condyles of the femur, helping them sit on the much flatter tibial condyles. The menisci also cushion the femur on the tibia, so are protective as we walk, run, and jump.
This article comes directly from content in the video series How We Move: The Gross Anatomy of Motion. Watch it now, on Wondrium.
Meniscus Tears
It’s important to note that the most medial edge of the medial meniscus is solidly connected to the medial collateral ligament, making the MCL less mobile than the lateral collateral ligament. This relationship also means that when the MCL tears—as from a sudden change in movement or an impact that puts excessive stress on the ligament—the medial meniscus is often damaged, as well. Since the LCL doesn’t attach to the lateral meniscus, the lateral meniscus is not torn as often.
One needs to remember that cartilage is avascular, so meniscus tears may heal slowly, poorly, or not at all. Not only can that depend on how severe the damage is, but sometimes the degree of healing relates to which part of the meniscus is damaged, as some parts are more vascularized than others.
Cruciate Ligaments
Between the medial and lateral condyles of the tibia, the cruciate ligaments attach to the tibia’s intercondylar eminence, which really consists of two small peaks: one for attachment of the anterior cruciate ligament, or ACL, and the other for the posterior cruciate ligament, known as the PCL.
Cruciate means “cross-like”, since these two ligaments form an anterior-to-posterior X within the knee joint. The modifiers anterior and posterior are really best understood relative to the attachments on the tibia.
In other words, the anterior cruciate ligament attaches to the anterior part of the intercondylar eminence on the tibia and passes posteriorly to attach to the posteromedial part of the lateral femoral condyle. The ACL prevents the femur from moving posteriorly on the tibia.
Extra-synovial
The PCL attaches on the posterior part of the tibia’s intercondylar eminence and passes anteriorly to attach to the anterolateral side of the femur’s medial condyle. The posterior cruciate ligament prevents the femur from moving anteriorly on the tibia.
Since they are within the capsule of the knee joint, the cruciate ligaments are said to be intracapsular, but interestingly, they are also said to be extra-synovial—meaning the cruciate ligaments are outside the thin, transparent synovial membrane that lines the joint.
Though synovial membranes line all freely movable diarthrotic joints, in this case, the knee’s synovial membrane folds around the cruciate ligaments, technically excluding them from being within the membrane, while still within the joint capsule.
Other Small Ligaments
There are a couple of other smaller knee joint ligaments called the arcuate and oblique popliteal ligaments—both help strengthen the posterior part of the joint. However, the anterior stability for the knee joint is largely derived from the tendon of the quadriceps femoris muscles and the patellar ligament that quadriceps tendon becomes.
In fact, the sleeve-like capsule is deficient anteriorly and is essentially replaced by the tendon of the quads and patellar ligament. Additional lateral stabilization is provided by the iliotibial tract and the vastus lateralis muscle, while vastus medialis helps with medial stability—so the strong quads help prevent knee injuries.
Common Questions about Ligaments of the Knee
The so-called tibial plateau is not exactly flat, since between the medial and lateral condyles of the tibia is a projection known as the intercondylar eminence. On either side of this intercondylar eminence sit the menisci of the knee. These fibrocartilaginous pads are articular discs, but they are usually called menisci at the knee.
Apart from the collateral and cruciate ligaments, there are a couple of other smaller knee joint ligaments called the arcuate and oblique popliteal ligaments—both help strengthen the posterior part of the joint.
The tibial collateral ligament, referred to by most as the medial collateral ligament, or MCL, is a relatively wide and flat ligament that connects the medial epicondyle of the femur to the medial condyle and proximal shaft of the tibia
