Knee Anatomy
About Your Knee
The knee is one of the body's largest and most complex joints, and this structure and one of the most stressed joints in the body.
It is vital for movement, can wear with age, and is vulnerable to injury.
Elements of the Knee
The knee is made up of four bones.
- Femur or thigh bone connects the hip to the knee.
- Tibia or shin bone connects the knee to the ankle.
- Patella or kneecap is the small bone in front of the knee and rides on the knee joint as the knee bends
- Fibula is a shorter and thinner bone running parallel to the tibia on its outside.
The knee joint acts like a hinge but with some rotation and is a synovial joint, which means it is lined by synovium. The synovium produces fluid lubricating and nourishing the inside of the joint.
Articular cartilage is the smooth surface at the end of the femur and tibia. It is the damage to this surface which causes arthritis.
Femur
The femur (thighbone) is the largest and strongest bone in the body. It is the weight-bearing bone of the thigh. It provides attachment to most of the muscles of the knee.
Condyle
The two femoral condyles make up the rounded end of the femur. Its smooth articular surface allows the femur to move quickly over the tibial (shinbone) meniscus.
Tibia
The tibia (shinbone), the second largest bone in the body, is the weight-bearing bone of the leg. The menisci incompletely cover the superior surface of the tibia, where it articulates with the femur. The menisci act as shock absorbers, protecting the articular surface of the tibia and assisting in knee rotation and stability.
Fibula
The fibula, although not a weight-bearing bone, provides attachment sites for the Lateral collateral ligaments (LCL) and the biceps femoris tendon.
The articulation of the tibia and fibula also allows a slight degree of movement, providing flexibility in response to the actions of muscles attaching to the fibula.
Patella
The patella (kneecap), attached to the quadriceps tendon above and the patellar ligament below, rests against the anterior articular surface of the lower end of the femur and protects the knee joint. The patella acts as a fulcrum for the quadriceps by holding the quadriceps tendon off the lower end of the femur.
Menisci
The medial and the lateral meniscus are thin C-shaped layers of fibrocartilage, incompletely covering the surface of the tibia where it articulates with the femur. The inner two-thirds of the meniscus has no blood supply; therefore, when damaged, the meniscus cannot undergo the normal healing process that occurs in the rest of the body.
The menisci act as shock absorbers, protecting the articular surface of the tibia and assisting in the rotation and stability of the knee. As secondary stabilisers, the intact menisci interact with the stabilising function of the ligaments and are most effective when the surrounding ligaments are intact.
Knee Ligaments
Anterior Cruciate Ligament (ACL)
The anterior cruciate ligament (ACL) is the major stabilising ligament of the knee. The ACL is located in the centre of the knee joint and runs from the femur (thigh bone) to the tibia (shin bone) through the centre of the knee.
The ACL prevents the femur from sliding backwards on the tibia (or the tibia sliding forwards on the femur). Together with the posterior cruciate ligament (PCL), the ACL rotationally stabilises the knee. Thus, if one of these ligaments is significantly damaged, the knee will be unstable when planting the foot of the injured extremity and pivoting, causing the knee to buckle and give way.
Posterior Cruciate Ligament (PCL)
More research needs to be done on the posterior cruciate ligament (PCL) because it is injured far less often than the ACL.
The PCL prevents the femur from moving too far forward over the tibia. The PCL is the knee’s primary stabiliser and is almost twice as strong as the ACL. It provides a central axis about which the knee rotates.
Collateral Ligaments
Collateral Ligaments prevent hyperextension, adduction, and abduction
- Superficial MCL (Medial Collateral Ligament) connects the medial epicondyle of the femur to the medial condyle of the tibia and resists valgus force.
- Deep MCL (Medial Collateral Ligament) connects the medial epicondyle of the femur with the medial meniscus.
- LCL (Lateral Collateral Ligament), entirely separate from the articular capsule, connects the lateral epicondyle of the femur to the head of the fibula and resists various forces. It is the main component of the Posterolateral Corner (PLC) Complex of the Knee, together with the Popliteus tendon and Fibular-Popliteal Ligament
