Anatomy of Normal Knee Joint
The knee is the largest weight-bearing joint in the body. Nearly normal knee function is needed to perform routine everyday activities. It is a complex hinge variety of a synovial joint. The knee is made up of the lower end of the thigh bone (femur), which moves on the upper end of the shin bone (tibia), and the knee cap (patella), which slides in a groove on the end of the femur. Large ligaments attach to the femur and tibia to provide stability. The long thigh muscles give the knee strength for movement.
The joint surfaces,where these three bones move against each other are covered with articular cartilage, a smooth tissue that cushions the bones and enables them to move easily. All remaining surfaces of the knee are covered by a thin, smooth tissue liner called the synovial membrane. In a healthy knee, this membrane releases a special fluid that lubricates the knee and almost eliminates the friction.
There are various structures inside and around the knee joint which help it during all its movements to keep it stable and balanced. Inside, there are two semicircular structures covering tibial surface, called menisci (singular- meniscus), medial and lateral in position. They work as shock absorbers in the joint and reduce stresses over the joint surface. Also, there are two cruciate ligaments, anterior and posterior, holding tibia and femur in opposite direction forming a letter ‘X’ in the middle of the joint. They restrict anterior and posterior translation of tibia over femur, respectively.
Outside the knee, there are two collateral ligaments, medial and lateral, which help to prevent deformation of the joint by bending of knee due to lateral (valgus) and medial (varus) forces. All these structures work synchronously to keep us moving forward confidently.