The knee joint, which appears like a simple hinge-joint, is one of the most complex joint.
It is essentially made up of four bones. The femur or thighbone is the bone connecting the hip to the knee. The tibia or shinbone connects the knee to the ankle. The patella (kneecap) is the small bone in front of the knee and rides on the knee joint as the knee bends. The fibula is a shorter and thinner bone running parallel to the tibia on its outside. This joint acts as a hinge but with some rotation.
The knee 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 surfaces at the end of the femur and tibia. It is the damage to this surface, which causes arthritis.
Knee Skeletal Anatomy
- Femur – The femur (thighbone) is the largest and the 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 for the rounded end of femur. Its smooth articular surface allows the femur to move easily 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 as well as assisting in rotation of the knee.
- 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 tibia and fibula, also allows a slight degree of movement, providing an element of 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 majority of the meniscus has no blood supply and for that reason, when damaged the meniscus is unable to undergo the normal healing process that occurs in the rest of the body.
In addition, meniscus begins to deteriorate with age, often developing degenerative tears. Typically, when the meniscus is damaged, the torn pieces begin to move in an abnormal fashion inside the joint.
The menisci act as shock absorbers, protecting the articular surface of the tibia as well as assisting in rotation 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.