Knee Anatomy

The knee is the most complex joint in your body and uses a delicately balanced system of bones, ligaments, and other structures to allow you to run, jump, perform cutting movements, and other advanced activities. The knee is made up of three bones: the femur (thigh bone), the tibia (shin bone), and the patella (kneecap). The two joints of the knee are the tibiofemoral joint (between the femur and tibia bones, this is the main knee joint) and the patellofemoral joint (between the kneecap and the trochlea, a groove on the front of the femur). The fibula bone is a thin bone on the outside of your lower leg that does not contribute to the knee joint, but is important to ankle stability.  Due to the geometry of the knee joint, it is inherently unstable and relies on ligaments, tendons, and other soft tissue (non-bony) structures for stability.  

• Ligaments: The knee ligaments support the knee through range of motion

  • Anterior cruciate ligament: This ligament is the most commonly discussed ligament, as it is commonly injured. It is located in the middle of the knee and runs from the back of the femur to the tibia. The ACL prevents the tibia from moving too far forward.

  • Posterior cruciate ligament: This ligament is also located in the middle of the knee and runs from the front of the femur to the back of the tibia. The PCL prevents the tibia from sliding too far backward.

  • Medial collateral ligament: This ligament is located along the inside of the knee and runs from a bony prominence on the inside of the femur to the inside of the tibia. It prevents the knee from collapsing inward.

  • Lateral collateral ligament: This ligament is located along the outside of the knee and runs from a bony prominence on the outside of the femur to the top of the fibula bone. This ligament works in concert with other soft tissue structures to prevent the knee from collapsing outward.

• Tendons: Two important tendons run along the front of the knee and help you bend and extend the knee.

  • Quadriceps tendon: This tendon is formed by the thigh muscles along the front of the thigh and attaches to the top of the patella.

  • Patellar tendon: This tendon runs from the bottom of the patella to the top of the tibia.

• Meniscus: The knee has two menisci that are located between the femur and tibia bones. The meniscus functions as a cushion between the bones and prevent bone-on-bone contact during activity. The meniscus plays an important role in knee health.

• Capsule: Every joint has an envelope around it to contain the joint and the joint fluid. When the knee becomes inflamed, there is an increase in joint fluid which causes the knee to swell

• Muscles: The knee is surrounded by large muscles that allow it to provide you with enough power to perform your daily activities and athletic pursuits.

  • The hamstring muscles are located in the back of the thigh and help the knee bend.

  • The quadriceps muscles are located in the front of the thigh and help the knee extend.

  • The gluteal muscles and core muscles play an important role in knee stability and are frequently included in physical therapy for knee conditions.

Other soft tissue structures in the knee include:

• Bursa: These structures are located between bone and the surrounding soft tissue around the knee. They serve as a cushion between the bones and surrounding tissues.

• Cartilage: This structure is present in all joints, where it’s called articular cartilage, and covers both ends of the bones in the joint. Cartilage allows the bones to glide easily as the joint is moved.