Knee anatomy and functions
The knee is the largest joint in the body and is made up of three main parts:
- The lower end of the thigh bone, or femur.
- The upper end of the shin bone, or tibia.
- The kneecap, or patella.
The knee is a complex hinge joint where the femur moves on the upper end of the tibia, and the patella slides in a groove on the end of the femur. The quadriceps, the long muscles on the front of the thigh, help strengthen the knee.
A smooth substance called articular cartilage covers the surface of the bones where they touch each other within the joint. This articular cartilage acts as a cushion between the bones. The rest of the surfaces of the knee joint are covered by a thin, smooth tissue liner called synovial membrane, which makes a small amount of fluid that acts as a lubricant so that the joint bones will not rub against each other. Between the femur and tibia the medial meniscus and the lateral meniscus (a specialised form of cartilage) help to distribute load, absorb shock, stabilise the knee and aid in lubrication. The knee bones are connected by strong ligaments which stabilise the knee and allow it to function properly. There are two cruciate ligaments (anterior cruciate ligament and posterior cruciate ligament) and two collateral ligaments (medial collateral ligament and lateral collateral ligament).
Muscles around the knee provide movement. The muscles at the front of the thigh, the quadriceps, straighten the knee, and those at the back, the hamstrings, bend the knee.
One of the most common causes of knee pain and loss of mobility is the wearing away of the joint's cartilage lining. This is commonly called as Arthritis. When this happens, the bones rub against each other, causing significant pain and swelling. The most common cause is osteoarthritis, though it can be caused by other inflammatory conditions like rheumatoid arthritis. Trauma or direct injury to the knee can also cause knee pain and osteoarthritis. Without cartilage there is no shock absorption between the bones in the joint, which allows stress to build up in the bones and contributes to pain.
Soft tissue conditions such as bursitis, quadriceps or patella tendonitis and variety of bony and cartilage conditions within the knee such as joint surface (chondral) damage, cartilage tears and unstable knee can also give rise to knee pain