Human Anatomy: Lower Extremity Kinematics

Study Notes

Identify the kinematics of lower extremity joints, relate the structure to function (mobility and stability), and relate important biomechanical issues in clinical situations.

The hip joint is formed by the union of the acetabulum of the pelvis and the head of the femur, forming a diarthrodial ball-and-socket joint with three degrees of freedom.

Bony structure:
- Acetabulum: a cup-like, concave socket with an acetabular labrum, a ring of wedge-shaped fibrocartilage that deepens the socket, increases the concavity of the acetabulum, and grasps the head of the femur to maintain contact with the acetabulum.
- Femoral head: a convex component of the ball-and-socket configuration of the hip joint, forming two-thirds of a sphere.
- Femoral neck: a junction between the head and shaft of the femur, attached to the shaft of the femur between the greater trochanter and lesser trochanter.

There are two angulations made by the head and neck of the femur on the shaft:
- Angle of inclination: occurs in the frontal plane, between the axis of the femoral neck and the axis of the femoral shaft.
- Angle of torsion: occurs in the transverse plane, between the axis of the femoral neck and the axis of the femoral condyles.

Angle of inclination:
- Normal value: approximately 150° in early infancy, decreasing to an average of 125° in normal adults, and somewhat smaller in women.
- Abnormal:
  - Coxa valga: neck shaft angle is increased (> 135°), directing the femoral head more superiorly in the acetabulum.
  - Coxa vara: neck shaft angle is decreased (< 125°).