Bones and Ligaments
Bones form the structure of the leg and support the body during standing and movement. The leg is composed of four bones; femur, patella, tibia and fibula. All of these except the latter articulate to form the knee joint. With the help of muscles, ligaments and tendons, this joint provides flexion, extension and rotation, giving the lower limb a range of movements. Bones also provide the attachment for the muscles of the leg through tendons.
The femur is the largest, longest and one of the strongest bones in the body. It is the only bone in the thigh, forming the hip joint proximally at its head and the knee joint distally at its condyles. Two additional protuberances are also present near the proximal end, known as the greater and lesser trochanters. The greater trochanter is large and directed backwards and laterally, providing the insertions of a number of gluteal muscles. The lesser trochanter is smaller and found at the base of the femur neck, facing backwards, and is the insertion of the iliopsoas.
The tibia is the major weight-bearing bone of the leg. It articulates with the femur proximally through its condyles, the fibula laterally and the talus distally, helping form the ankle joint.
The fibula is the smaller bone of the lower leg. It attaches below the lateral condyle of the tibia proximally, and articulates with the tulus distally, forming the lateral part of the ankle joint.
The patella is a thick, flat, triangular-shaped bone situated at the front of the knee joint. Having attachments to the quadraceps tendon, its main function is to increase the angle of the joint, therefore increasing the strength of leverage during extension by about 30%. It is the largest sesamoid bone in the body and also serves to protect the anterior surface of the joint. The patellar ligament is continuous with the quadraceps tendon and inserts into the tibial tubercle. It is used clinically for the stretch reflex as it is easily palpable.
The knee joint is the largest joint in the body and, due to its complexity, is the most prone to injury. It is a synovial joint made up of three bones: the femur, patella and tibia. These are all attached through ligaments, which aid in stabilising the joint. The fibula is also attached to the femur through a ligament, however it articulates with the tibia and does not assist with movement of the joint itself. The extremities of each bone are covered in cartilage, known as the menisci. This protect the bones by reducing friction between them during movement and by acting as shock-absorbers. The two groups of muscles, known as the quadriceps and the hamstrings, provide movement to the joint. Contraction of the quadriceps lead to extension of the knee by pulling upwards on the patella, whereas contraction of the hamstrings opposes this action as they provide flexion. Both groups of muscle also produce a slight medial or lateral rotation whilst in a flexed position. The major components of the knee joint are listed below:
- Medial meniscus - Runs between the medial condyle of the femur and the medial condyle of the tibia. It is also attached to the medial collateral ligament.
- Lateral meniscus - Runs between the lateral condyle of the femur and the lateral condyle of the tibia. It is also attached to the popliteal muscle.
- Medial collateral ligament - Runs from the medial epicondyle of the femur to the medial condyle of the tibia. It is also attached to the medial meniscus. It protects the medial knee from being bent open with a lateral force.
- Lateral collateral ligament - Runs from the lateral epicondyle of the femur to the head of the fibula. It protects the lateral knee from being bent open with a medial force.
- Anterior cruciate ligament - Runs from the anterior tibia to the posterior lateral femur. It prevents the tibia from moving forwards.
- Posterior cruciate ligament - Runs from the posterior tibia to the anterior medial femur. It prevents the tibia from moving backwards.