Understanding your knee

Plymouth Orthopaedic and Sports Injury Clinic

The knee joint is the articulation between the thigh bone (femur) and leg bone (tibia). The knee cap (patella) articulates with a groove on the front of the lower femur (trochlea). The powerful quadriceps muscles attach to the patella, which then attaches to the tibia via the short but strong patella tendon. At the back, hamstring muscles attach via long tendons to the upper tibia.

These muscles not only move the knee, but also play a role in helping the strong ligaments to stabilise the joint. Within the middle of the knee, the anterior and posterior cruciate ligaments (ACL and PCL) play a critical role in stability. The medial collateral ligament stabilises the inner side of the knee and the lateral collateral the outer side (MCL and LCL). Toward the back of the knee, the collateral ligaments blend with a thick capsule to form the posteromedial and posterolateral corner structures. The patella is held in its groove, named the trochlea, by the medial and lateral retinaculum.

The bottom of the femur demonstrates two large knuckles called the medial and lateral condyles. These articulate with the medial and lateral tibial plateaux. Two very strong rubber like, c-shaped washers help to hold the condyles in place and distribute loads. We call these the medial and lateral meniscus.

To confuse us, the meniscus is often called the cartilage (“torn cartilage”) when in fact it is not cartilage at all! The real cartilage is the glistening white surface that lines the end of the bones where they form a joint. It is exactly the same as the surface you see inside the joint on a leg of lamb! We call this hyaline cartilage, and it is the almost friction free bearing surface which allows our joints to glide smoothly.

Damage to this surface whether caused by wear and tear, disease or injury, is one the most important reasons for the knee joint to cause symptoms.

The Knee Joint “through the ages”

Whilst different knee problems do not always present at a certain age, it is quite a useful concept to consider the adolescent knee, the sports person’s knee and the elderly knee! This is not an ageist approach, and of course there can be considerable overlap.