Knee Anatomy
The knee joint is one of the most important joints in the human body. It supports your entire body weight. When you run or jump, the force of impact on your knees is many times your body weight. As a result, your knees are prone to wear and tear.
Inside Your Knee Joint
Femur (thigh bone)
Tibia (shin bone)
Patella (knee cap)
This is found on the lower end of the femur, the upper end of the tibia and on the undersurface of the patella. Cartilage protects the bones and enables the joint surfaces to slide smoothly over each other.
The medial and lateral menisci are specialised cartilage cushions that are found between the femur and tibia. They improve the way the femur and tibia articulate and they act as shock absorbers in your knee.
The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) control the movement of the tibia in relation to the femur in a forward and backward direction. The ACL is more easily damaged than the PCL. An injury usually occurs when you suddenly change direction while playing sport. A torn ACL causes the knee to ‘give way’. This ligament is unable to heal itself and unless it is surgically repaired, your knee will feel progressively more unstable. The PCL on the other hand is the strongest ligament in your knee. A torn PCL does not impair your ability to play sport and if it is an isolated injury it does not need to be repaired.
Bursae are pockets of synovial fluid that cushion your knee joint. Your knee joint is surrounded by a joint capsule which is lined with a synovial membrane. This synovial membrane produces synovial fluid which bathes all the structures in your knee joint and prevents friction.
Outside Your Knee Joint
The medial and lateral collateral ligaments protect your knee from sideward forces.
The patellar tendon attaches the patella to the upper end of the tibia. It is an extension of the quadriceps (thigh) muscle that covers your femur in front.
Movements of the Knee Joint
Your knee is a hinge joint which allows for the following movements:
- Flexion (bending)
- Extension (straightening)
- Medial and lateral rotation (turning in an inward and outward direction)
The movements of the knee joint are controlled by the large muscles of your thigh and lower leg. These muscles and their tendons also cover and protect your knee joint.
Common Symptoms of Knee Problems
- Pain and discomfort
- Swelling
- Locking| Feeling like your knee is fixed in a certain position and being unable to fully straighten your leg.
- Giving Way| The feeling of your knee buckling under you and being unable to support your weight.
Investigating Knee Problems
An X-Ray of the knee is the first investigation that is done to assess your knee. Special views may be required. A CT or MRI scan of your knee gives more detailed information particularly when soft tissues such as menisci and ligaments are involved. A knee arthroscopy is also used to investigate knee problems. It is an operation that involves inserting a camera into the knee joint to look directly at the structures within, and to determine the nature and extent of a problem.
Knee Terminology
- Arthroscopy| An operation through a small skin incision to look inside a joint with a camera.
- Arthroplasty| A joint replacement.
- Bursae| Pockets of fluid that cushion the knee joint.
- Cartilage| Connective tissue that is found on the lower end of the femur, the upper end of the tibia and on the undersurface of the patella. Cartilage protects the bones and allows them to rub against each other.
- Ligaments| Connective tissue that attach one bone to another.
- Menisci| The medial and lateral meniscus are specialised cartilages that lie within the knee joint between the femur and tibia. They act as shock absorbers.
- Osteoarthritis| A degenerative condition whereby the cartilage in the knee joint wears away resulting in the femur and tibia rubbing directly against each other.
- Plica| A fold in the synovial membrane (joint lining) of the knee.
- Posterolateral Corner| The group of ligaments, tendons and soft tissues that are found laterally (outer side) at the back of the knee joint.
- Prosthesis| A man-made component that is designed to resemble normal anatomy. In the knee joint the femur and tibia are replaced by metal prostheses while the menisci are replaced by plastic components.
- Tendons| Connective tissue that attach muscles to bones.