Biomechanics of the hip Prof. Sung-Jae, Lee Ph.D Inje Univ.

Introduction Introduction Anatomical considerations Anatomical considerations The Acetabulum The Acetabulum The Femoral Head The Femoral Head The Femoral Neck The Femoral Neck Kinematics Kinematics Range of Motion Range of Motion Surface joint Motion Surface joint Motion Kinetics Kinetics Statics Statics Dynamics Dynamics Effect of External Support on Hip Joint Reaction Force Effect of External Support on Hip Joint Reaction Force

Introduction One of the largest and most stable joint: One of the largest and most stable joint: The hip joint The hip joint Rigid ball-and-socket configuration Rigid ball-and-socket configuration (Intrinsic stability) (Intrinsic stability)

Anatomy Composed of : Composed of : Head of femur Head of femur Acetabulum of pelvis Acetabulum of pelvis Wide range of motion Wide range of motion Walking, sitting, squatting Walking, sitting, squatting

Anatomy Surrounding large, strong muscles Surrounding large, strong muscles

Acetabulum Concave component of ball and socket joint Concave component of ball and socket joint Cover with articular cartilage Cover with articular cartilage Provide with static stability Provide with static stability

Acetabulum Facing obliquely forward, outward and downward Facing obliquely forward, outward and downward

Acetabulum Labrum: a flat rim of Labrum: a flat rim of fibro cartilage fibro cartilage Transverse acetabular ligament Transverse acetabular ligament

Acetabulum Unload: small diameter Unload: small diameter region region in vitro Load distribution in vitro Load distribution

The femoral head Femoral head : convex component Femoral head : convex component Two-third of a sphere Two-third of a sphere Cover with cartilage Cover with cartilage Rydell (1965) suggested : most load Rydell (1965) suggested : most load superior quadrant superior quadrant

The femoral neck Frontal plane (the neck-to-shaft angle) Frontal plane (the neck-to-shaft angle) Transverse plane (the angle of anteversion) Transverse plane (the angle of anteversion)

Neck-to-shaft angle : Neck-to-shaft angle : 125 º, vary from 90 º to 135 º 125 º, vary from 90 º to 135 º Effect : lever arms Effect : lever arms

Neck-to-shaft angle & Abductor muscle force

Angle of anteversion :12 º Angle of anteversion :12 º Effect : during gait Effect : during gait >12 º :internal rotation >12 º :internal rotation <12 º :external rotation <12 º :external rotation

Femoral neck :Cancellous bone, Femoral neck :Cancellous bone, medial and lateral trabecular system medial and lateral trabecular system *Joint reaction force parallels the medial trabecular system *Joint reaction force parallels the medial trabecular system

medial trabecular system Joint reaction force Frankel, 1960

Femoral Intertrochanteric Fractures *The femur neck is the most common fracture site in elderly persons

Kinematics Hip motion takes place in all three planes: Hip motion takes place in all three planes: sagittal (flexion-extension) sagittal (flexion-extension) frontal (abduction-adduction) frontal (abduction-adduction) transverse (internal-external rotation) transverse (internal-external rotation) Muscle, ligament and configuration … Muscle, ligament and configuration … asymmetric asymmetric

Kinematics Rang of motion : sagittal, frontal, transverse Rang of motion : sagittal, frontal, transverse 0~140 0~30 0~150~25 0~900~70

Kinematics 35 to 40° One gait cycle Frontal plane Transverse plane Toe-off

Kinematics Murray and coworkers (1969) studied the walking patterns of 67 normal men of similar weight and height ranging in age from 20 to 87 years and compared the gait patterns of older and younger men Murray and coworkers (1969) studied the walking patterns of 67 normal men of similar weight and height ranging in age from 20 to 87 years and compared the gait patterns of older and younger men

Kinematics Old man : shorter strides Old man : shorter strides Decrease: Decrease: Rang of hip flexion, Rang of hip flexion, extension extension Plantar flexion of ankle Plantar flexion of ankle Heel-floor angle Heel-floor angle Old manYoung man

Kinematics hip flexion of at least 120 ° hip flexion of at least 120 ° Abduction and external rotation of at least 20 ° Abduction and external rotation of at least 20 °

Surface Joint Motion Surface motion in the hip joint can be considered as gliding of the femoral head on the acetabulum. Surface motion in the hip joint can be considered as gliding of the femoral head on the acetabulum. Center of rotation: Center of rotation: estimated at the center of the femur head estimated at the center of the femur head

Kinetics Forces acting on the hip joint : must be understood Forces acting on the hip joint : must be understood Prostheses design Prostheses design Fixation devices Fixation devices Osteotomy operation Osteotomy operation Rehabilitation Rehabilitation STATICS and DYNAMICS STATICS and DYNAMICS

Statics Two-leg stance : without muscle contraction, stabilization by joint capsule and capsular ligament Two-leg stance : without muscle contraction, stabilization by joint capsule and capsular ligament Calculation of the joint reaction force becomes simple Calculation of the joint reaction force becomes simple Two-leg to single-leg stance : gravity line change Two-leg to single-leg stance : gravity line change Two methods : the simplified free-body technique Two methods : the simplified free-body technique & mathematical method & mathematical method

Neutral position Shoulders are tilted max. over supporting hip joint Shoulders tilted oppositePelvis sags from support Single-leg

Solvent (1) Free-body for coplanar forces (three force member)

Solvent (2) free-body for equilibrium equation

equilibrium equation (moment) It’s necessary to know b, c for solving A

equilibrium equation(x,y force)

Dynamics Loads on the hip joint during dynamic activities Loads on the hip joint during dynamic activities

HS TO

Several factors : Several factors : a wider female pelvis a wider female pelvis a difference in the inclination of the femoral a difference in the inclination of the femoral neck-to-shaft angle neck-to-shaft angle a difference in footwear a difference in footwear and differences in the general pattern of gait and differences in the general pattern of gait

In vivo measurement of force: From prosthesis An increase in muscle activity at the faster cadence resulted in higher force on the prosthesis.

Nail plate : osteotomy or neck fracture

Thank you ! Thank you !