Anatomy of the Knee
Your knees are two of the largest joints in your body. The knee joint is made up of 3 bones along with tendons, ligaments and other tissue. We’ve broken down the complexities of the knee into its various components. Many of our patients find that learning about normal knee anatomy helps them to better understand their knee injury or condition.
First, it’s important to note that many of the structures in the knee are named by location.
- Anterior: refers to a structure toward the front of the body
- Posterior: refers to a structure toward the back of the body
- Midline: an imaginary line running down the center of the body
- Medial: refers to a structure closer to the midline (the medial side of the knee is the inner side of the knee)
- Lateral: refers to a structure farther away from the center of the body (the lateral side of the knee is the outer side of the knee)
The knee joint consists of the femur (thigh bone) and the tibia (shin bone). The patella (knee cap) is located on the front of the knee joint. The joint surfaces of these bones are lined with articular cartilage. Articular cartilage provides a smooth joint surface. The knee joint is a synovial joint. Synovial joints are surrounded by a joint capsule and filled with a fluid called synovial fluid. Synovial fluid lubricates the joint.
Two cartilage cushions called menisci separate the tibia (shin bone) and the femur (thigh bone). Menisci is the plural term for meniscus. The two menisci are the medial meniscus and the lateral meniscus. The menisci serve two important roles. First, they help make the tibia and the femur fit together better. Second, the menisci act as cushions to distribute the impact of weight bearing across the joint surface.
There are 4 main ligaments that provide stability to the knee:
- Anterior Cruciate Ligament ( ACL )
- Keeps the tibia (shin bone) from moving forward on the femur (thigh bone)
- Posterior Cruciate Ligament ( PCL )
- Keeps the tibia (shin bone) from moving backward on the femur (thigh bone)
- Medial Collateral Ligament ( MCL )
- Prevents the knee from buckling inward
- Lateral Collateral Ligament (LCL)
- Prevents the knee from buckling outward
The quadriceps muscle is located on the front of the thigh. When the quadriceps muscle tightens, the knee extends (straightens). The quadriceps connects to the tibia (shin bone) via a long tendon across the front of the knee joint. The patella (knee cap) sits within this tendon. This tendon is divided into two parts. The quadriceps tendon attaches the quadriceps muscle to the top of the patella. The patellar tendon attaches the patella to the tibia.
Another major muscle group near the knee is the hamstring muscle group. The hamstring group is made up of three muscles that cross the back of the knee. These muscles form the muscle mass along the back of the thigh.