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

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

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

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

5. Anatomy • Surrounding large, strong muscles

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

7. Acetabulum • Facing obliquely forward, outward and downward

8. Acetabulum • Labrum: a flat rim of fibrocartilage • Transverse acetabular ligament

9. Acetabulum • Unload: small diameter region • in vitro Load distribution

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

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

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

13. Neck-to-shaft angle & Abductor muscle force

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

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

16. medial trabecular system Joint reaction force Frankel, 1960

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

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

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

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

21. 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

22. Old man Young man Kinematics Old man : shorter strides • Decrease: Rang of hip flexion, extension Plantar flexion of ankle Heel-floor angle

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

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

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

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

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

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

29. Solvent (2) free-body for equilibrium equation

30. equilibrium equation(moment) It’snecessary to knowb,c for solving A

31. equilibrium equation(x,y force)

34. Dynamics • Loads on the hip joint during dynamic activities

35. TO HS

36. 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

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

40. Nail plate : osteotomy or neck fracture

44. Thank you !