Chapter 8

At the conclusion of this chapter, the student should be able to:

• 1. Name, locate, and describe the structure and ligamentous reinforcements of the articulations of the knee, ankle, and foot.
• 2. Name and demonstrate the movements possible in the joints of the knee, ankle, and foot, regardless of starting position.
• 3. Name and locate the muscles and muscle groups of the knee, ankle, and foot, and name their primary actions as agonists, stabilizers, neutralizers, or antagonists.
• 4. Analyze the fundamental movements of the lower leg and foot with respect to joint and muscle actions.
• 5. Describe the common injuries of the leg, knee, and ankle.
• 6. Perform an anatomical analysis of the lower extremity in a motor skill.

The knee joint is the largest and most complex joint in the human body. It is a masterpiece of anatomical engineering. Placed midway down each supporting column of the body, it is subject to severe stresses and strains in its combined functions of weight bearing and locomotion. To take care of the weight-bearing stresses, it has massive condyles; to facilitate locomotion it has a wide range of motion; to resist the lateral stresses due to the tremendous lever effect of the long femur and tibia, it is reinforced at the sides by strong ligaments; to combat the downward pull of gravity and to meet the demands of such violent locomotor activities as running and jumping, it is provided with powerful musculature. It would be difficult, indeed, to find a mechanism better adapted for meeting the combined requirements of stability and mobility than the knee joint.

### Structure

Although the knee is classified as a hinge joint, its bony structure resembles two condyloid or ovoid joints lying side by side, yet not quite parallel (Figure 8.1). The lateral flexion permitted in a single ovoid joint is not possible in the knee joint because of the presence of the second condyle. The two rockerlike condyles of the femur rest on the two slightly concave areas on the top of the tibia’s broad head. These articular surfaces of the tibia are separated by a roughened area, called the intercondyloid eminence, which terminates both anteriorly and posteriorly in a slight hollow but rises at the center to form two small tubercles like miniature twin mountain peaks (Figure 8.2). During knee extension, the intercondyloid tubercles enter the intercondyloid fossa of the femur. The medial articular surface of the tibia is oval; the lateral is smaller and more nearly round. Each is overlaid by a somewhat crescent-shaped fibrocartilage, known as a semilunar cartilage, or meniscus.

###### Figure 8.1

Articulating surfaces of knee joint.

###### Figure 8.2

Anterior and posterior views of bones of knee joint.

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