THE KNEE JOINT
• Femur – thigh bone
• Tibia – larger of the two lower leg bones
• Fibula – smaller of the two leg bones
• Patella – kneecap
As in all joints, the ends of the bones are covered with hyaline, or articular, cartilage that protects the ends of the bones and allows them to glide over each other during movement. Loss of this cartilage can lead to osteoarthritis.
The knee can also be seen as consisting of two compartments, one on the inside of the knee (medial) and one on on the outside (lateral). Each of these contains a meniscus, or pad of more fibrous cartilage, that acts as a shock absorber and helps to stabilise the knee.
The two joints of the knee are:
• Femoral-tibial – the main knee joint between the femur and the tibia
• Patellofemoral – between the kneecap and the femur
The femoral-tibial joint is mainly held together by four ligaments:
• Anterior cruciate ligament
• Posterior cruciate ligament
• Medial collateral ligament
• Lateral collateral ligament
The two cruciate (cross-shaped) ligaments are found at the center of the knee and stop the tibia moving too far forwards or backwards, while the two collateral ligaments are on the inside and outside of the knee and help attach the femur to the lower leg bones. If any of these ligaments are injured, the knee can become unstable.
In the patellofemoral joint, the kneecap moves in a groove on the femur called the trochlea, and both sides are covered in articular cartilage that eases movement.
Above the knee, the quadriceps (four-headed) muscles of the thigh help to straighten the knee and stop the tibia moving backwards, while the hamstring muscles, at the back of the knee, help to bend the knee and stop the tibia moving too far forwards.
The progressive degeneration of articular cartilage is an underlying problem in the pathogenesis of osteoarthritis (OA) as well as in rheumatoid arthritis (RA) and other inflammation arthritis. It leads to a loss of joint function, frequently accompanied by debilitating pain.
The physical and economic burden of OA is enormous, affecting up to 15% of the total population (>50% of the aging population over 60 years of age)