Knee Anatomy

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.