Human Anatomy: Lower Extremity Kinematics

Lower Extremity Kinematics and Clinical Relevance

• 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

• 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.

Structure of the Hip Joint

• 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.

Angulations of the Femur

• 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.

Angles of the Femur

• 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°).