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The Hip

Functions of the Hip
Joint Structure of the Hip
Kinematics of the Hip Joint
Muscle actions at the Hip Joint
Hip Joint Stability
Mechanism of Injury at the Hip Joint

Objectives： After studying this topic, the students will be able to

1. to identify the structure of the hip joint, including joint type, articular shape, and the surrounding tissues
2. to describe joint motions occurring at the hip joint, including osteokinematic and arthrokinematic movements, muscle actions, and factors checking hip motions
3. to understand the stability mechanism of the hip joint and the possible mechanisms of injury
4. to identify the malalignment of the weight bearing joints in different cardinal planes
5. to explicate the trabecular system and its relationship to weight bearing

1. Neumann DA (2002).  Hip.  In Neumann DA: Kinesiology of the Musculoskeletal System: Foundations for Physical Rehabilitation. Philadelphia: Mosby.  Chapter 12, pp. 387-433.
2. Smith LK, Weiss EL, Don Lehmkuhl L (1996). Brunnstrom's Clinical Kinesiology, 5th ed.  Philadelphia, F. A. Davis.  Chapter 8, pp. 266-300.
3. Nordin M & Frankel VH (2001).  Biomechanics of the hip.  In Nordin M & Frankel VH: Basic Biomechanics of the Musculoskeletal System.  Philadelphia: Lippincott Williams & Wilkins. Chapter 8, pp.202-221.

Functions of the Hip

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Joint Structure of the Hip

Hip Joint

proximal component： pelvis concave acetabulum that faces anterior, inferior, and lateral distal component： femur concave femoral head that faces anterior, superior, and medial (anteversion) joint type： ball-and-socket joint motions： convex on concave hip flexion/ extension hip abduction/ adduction hip external/ internal rotation DOF = 3
closed-packed position： maximum extension, abduction, and internal rotation not associated with the position of maximum congruency (90º of hip flexion with moderate abduction and external rotation) against 13% of body weight (swing phase) to 300% of body weight (stance phase) during walking

Hip Joint

Angle of Inclination

synonym： head-neck angle angle between the longitudinal axis of the femoral neck to that of the femoral shaft in the frontal plane statistics normal adults： 125º newborn： 140-150º frontal plane deformities coxa valga： angle of inclination > 125º coxa vara： angle of inclination < 125º

Angle of Anteversion

synonym： angle of anteversion angle of the longitudinal axis of the femoral neck to the line connecting posterior aspect of both femoral condyles in the transverse plane statistics normal adults and child > 6 years old： 12-15º newborn： 30-40º transverse plane deformities anteversion： resulting in toeing-in gait (內八字) retroversion： resulting in toeing-out gait (外八字)

Malalignment of Weight-Bearing Joints

Trabecular System of the Femur

function： to accommodate to the mechanical stresses and strains created by the transmission of forces between femur and pelvis classification medial trabecular system from medial cortex of upper femoral shaft radiating outward to superior cortex of femoral head parallel to joint reaction force on femoral head during single leg stance lateral trabecular system from lateral cortex of upper femoral shaft radiating outward to inferior cortex of the femoral head in response to forces created during hip abductor contraction or to tensile stresses created by gravitational moments of force on femoral head

accessory trabecular system medial accessory lateral accessory zone of weakness the area where the trabeculae do not cross at right angles less reinforcement by trabeculae more potential for injury

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Kinematics of the Hip

Hip Flexion/ Extension

Hip Abduction

Hip Internal/ External Rotation

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Muscles Across the Hip

Hip Flexors

Hip Extensors

Hip Abductors

Hip External Rotators

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Hip Stability

Factors Affecting Stability of the Hip Joint

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Mechanism of Injury at the Hip

Direct stress

Repeated stresses

Deformities

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