Biomechanics of the hip Prof SungJae Lee Ph

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

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

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

Anatomy Composed of : n Head of femur n Acetabulum of pelvis n n 18 16 7 9 Wide range of motion Walking, sitting, squatting

Anatomy n Surrounding large, strong muscles

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

Acetabulum n Facing obliquely forward, outward and downward

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

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

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

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

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

Neck-to-shaft angle & Abductor muscle force

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

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

Joint reaction force medial trabecular system Frankel, 1960

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

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

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

Kinematics n 0~140 Rang of motion : sagittal, frontal, transverse 0~15 0~30 0~25 0~90 0~70

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

Kinematics n 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 n Decrease: Rang of hip flexion, extension Plantar flexion of ankle Heel-floor angle Old man Young man

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

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

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

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

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

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 n Loads on the hip joint during dynamic activities

HS TO

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