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The bone between the hip and the knee is the femur. It is the longest and strongest bone in the body. The femur articulates proximally with the acetabulum and distally with the tibia and patella. The knee joint is formed by articulations of the femur, tibia, and patella. The knee joint enables flexion, extension, and minimal rotation of the femur and tibia. Also, it plays an important role in supporting the weight of the body during static positions and dynamic movement during gait.

Actions of the Knee Complex

The articulations between the femur, tibia, and patella form the knee joint and enable the following actions (Figure 36-1A):

  • Flexion. Movement in the sagittal plane, decreasing the knee joint angle.
  • Extension. Movement in the sagittal plane, increasing the knee joint angle.
  • Medial rotation. Movement toward the midline in the transverse or axial plane.
  • Lateral rotation. Movement away from the midline in the transverse or axial plane.

Figure 36-1

A. Actions of the knee joint. B. Compartments of the thigh. C. Muscles of the anterior compartment of the thigh.

Big Picture

The muscles of the thigh are divided by their fascial compartments (anterior, medial, and posterior) and may cross the hip or knee joint (Figure 36-1B). Identifying which joints the muscles cross and the side on which they cross can provide useful insight into the actions of these muscles (Table 36-1).

Table 36-1. Muscles of the Thigh

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