Clinical Anatomy: Cartilage in the Knee Joint
The knee joint is basically a hinge joint that lets you flex and extend the leg, although there is a small amount of gliding movement as well. Although it’s a large joint, it isn’t as stable as many other joints, so injuring the knee is fairly easy to do (much to the disappointment of many athletes).
The knee joint is formed by the articulation of the condyles of the distal femur with the articular surfaces of the proximal tibia. The fibular head also articulates with the lateral part of the tibia. The patella articulates with the patellar surface of the femur, and it rests in the quadriceps tendon and helps protect the knee joint.
The articular surfaces of the main part of the knee joint (technically called the femorotibial articulations) are found on the articular surfaces between the condyles of both bones. They’re covered with hyaline cartilage. In addition, the knee joint is surrounded by a joint capsule that’s made of two layers:
An external thin layer of fibrous connective tissue
An inner synovial membrane that lines the joint
The infrapatellar fat pad lies anterior to the joint capsule but behind the patella. It helps cushion the knee joint.
The infrapatellar fat pad can become pinched between the condyles of the femur and the patella due to direct impact to the knee. The fat pad is quite sensitive, so this pinching can become very painful, especially if the tissue becomes inflamed.
Two crescent-shaped pieces of fibrocartilage called menisci are located on the articular surfaces of the tibia. Each meniscus is thinner at the interior part of the knee joint and thicker externally. They work as shock absorbers in the knee and help to balance your weight over the entire joint.
The medial meniscus is shaped like the letter C and is wider at the front than at the back. It’s attached to the intercondylar area of the tibia and to the medial (tibial) collateral ligament. The lateral meniscus is smaller and rounder in shape. It has a little more movement compared to the medial meniscus.
Tearing a meniscus is common and can affect the function of the knee. It’s usually caused by a quick twisting or turning movement of the knee while the foot is planted, so it’s common in sports. The menisci get thinner with age, so they’re also easier for older people to tear.
A minor tear may hurt for two to three weeks and be treated with rest and ice, but a moderate tear can cause pain for years if not treated. Severe tears result in bits of the torn meniscus moving into the joint space, causing the knee to pop, click, catch, or lock into place. A torn meniscus may require surgery to repair the meniscus or trim the edges.
The knee is susceptible to a couple types of arthritis:
The knee is commonly affected by rheumatoid arthritis, which is an autoimmune disease that damages joint cartilage.
Knees that have been injured are also at a greater risk for developing osteoarthritis, which can develop many years after fractures or damage to the ligaments or menisci.
Treatment for arthritis may include medications for pain relief and inflammation, specific exercises, and possibly surgery in severe cases.