BIOMECHANICS OF HIP JOINT BY Dr. VIKRAM

HIP JOINT BIOMECHANICS

1. BIOMECHANICS OF HIP JOINT Seminar by Dr. T. Vikram M.S ORTHO Prathima institute of medical sciences karimnagar

2. INTRODUCTION The hip joint, or coxofemoral joint, is the articulation of the acetabulum of the pelvis and the head of the femur diarthrodial ball-and-socket joint three degrees of freedom: flexion/extension in the sagittal plane abduction/adduction in the frontal plane medial/lateral rotation in the transverse plane

3. The primary function of the hip joint is to support the weight of the head, arms , and trunk (HAT) both in static erect posture and in dynamic postures such as ambulation, running, and stair climbing .

4. STRUCTURE OF THE HIP JOINT Proximal Articular Surface Acetabulum The opening of the acetabulum is approximately laterally inclined 50°; anteriorly rotated (anteversion) 20°; and anteriorly tilted 20° in the frontal, transverse, and sagittal planes , respectively

5. Acetabular depth can be measured as the center edge angle of Wiberg

6. Center edge angles are classified as follows : definite dysplasia less than 16° possible dysplasia 16° to 25° and normal greater than 25° In addition, abnormalities in acetabular depth, inclination, and version (abnormal positioning in the transverse plane ) can also affect femoral head coverage

7. Anteversion of the acetabulum exists when the acetabulum is positioned too far anteriorly in the transverse plane Retroversion exists when the acetabulum is positioned too far posteriorly in the transverse plane

8. Acetabular labrum The entire periphery of the acetabulum is rimmed by a ring of wedge-shaped fibrocartilage called the acetabular labrum Deepens the socket, increases the concavity of the acetabulum, grasping the head of the femur to maintain contact with the acetabulum It enhances joint stability by acting as a seal to maintain negative intra-articular pressure Also provide proprioceptive feedback

9. Distal articular surface The head of the femur fovea or fovea capitis ligament of the head of the femur ( ligamentum teres)

10. ANGULATION OF THE FEMUR There are two angulations made by the head and neck of the femur in relation to the shaft Angle of inclination occurs in the frontal plane between an axis through the femoral head and neck and the longitudinal axis of the femoral shaft A ngle of torsion occurs in the transverse plane between an axis through the femoral head and neck and an axis through the distal femoral condyles

11. 1.ANGLE IF INCLINATION OF FEMUR The angle of inclination of the femur approximates 125 ° Normal range from 110° to 144° in the unimpaired adult With a normal angle of inclination, the greater trochanter lies at the level of the center of the femoral head A pathological increase in the medial angulation between the neck and shaft is called coxa valga A pathological decrease is called coxa vara

12. Both coxa vara and coxa valga can lead to abnormal lower extremity biomechanics altered muscle function,and gait abnormalities

13. 2.ANGLE OF TORSION OF THE FEMUR The angle of torsion of the femur can best be viewed by looking down the length of the femur from top to bottom An axis through the femoral head and neck in the transverse plane will lie at an angle to an axis through the femoral condyles , with the head and neck torsioned anteriorly (laterally ) with regard to an angle through the femoral condyles

14. In the adult, the normal angle of torsion is considered to be 10° to 20°, 15° for males and 18° for females Femoral anteversion is considered to exist when angle of anterior torsion is greater than 15° to 20 ° A reversal of anterior torsion, known as femoral retroversion , occurs when angles are less than 15° to 20°

15. Femoral anteversion is associated with increased medial rotation ROM and concurrent decreased lateral rotation so that the total excursion of hip rotation motion remains the same Anteversion of the femoral head reduces hip joint stability because the femoral articular surface is more exposed anteriorly The line of the hip abductors may fall more posterior to the joint, reducing the moment arm for abduction

16. When the femoral head is anteverted, pressure from the anterior capsuloligamentous structures and the anterior musculature may push the femoral head back into the acetabulum , causing the entire femur to rotate medially The knee joint axis through the femoral condyles is now turned medially Medial rotation of the femoral condyles alters the plane of knee flexion/extension and results, at least initially,in a toe-in gait and a compensatory lateral tibial torsion develop

17. A n anteverted femur will also affect the biomechanics of the patellofemoral joint at the knee and of the subtalar joint in the foot The effect of femoral anteversion may also be seen at the knee joint

18. COXA VARA In adolescence, growth of the bone results in a more oblique orientation of the epiphyseal plate The epiphyseal obliquity makes the plate more vulnerable to shear forces at a time when the plate is already weakened by the rapid growth that occurs during this period of life

19. Weight-bearing forces may slide the femoral head inferiorly, resulting in a slipped capital femoral epiphysis in case of coxa vara Disadvantage of increasing the bending moment along the femoral head and neck The increased shear force along the femoral neck will increase the predisposition toward femoral neck fracture

20. COXA VALGA Coxa valga also decreases the amount of femoral articular surface in contact with the dome of the acetabulum. As the femoral head points more superiorly, there is a decreasing amount of coverage from the acetabulum superiorly. Consequently, decreases the stability of the hip and predisposes the hip to dislocation The resulting need for additional abductor muscle force may predispose the joint to arthrosis or may functionally weaken the joint, producing energy-consuming and wearing gait deviations

21. ARTICULAR CONGRUENCE In the neutral or standing position, the articular surface of the femoral head remains exposed anteriorly and somewhat superiorly Articular contact between the femur and the acetabulum can be increased in the normal non-weight-bearing hip joint by a combination of flexion, abduction, and slight lateral rotation

22. HIP JOINT CAPSULE Both joint capsule and ligamentum teres provide stability of the hip joint during distractive forces

23. HIP JOINT LIGAMENTS I liofemoral ligament(Y ligament of Bigelow) Pubofemoral ligament Ischiofemoral ligament

24. STRUCTURAL ADAPTATIONS TO WEIGHT BEARING In standing or upright weightbearing activities , at least half the weight of the HAT ( the gravitational force) passes down through the pelvis to the femoral head, whereas the ground reaction force ( GRF) travels up the shaft.

25. These two forces, nearly parallel and in opposite directions, create a force couple with a moment arm (MA) equal to the distance between the superimposed body weight on the femoral head and the GRF up the shaft. These forces create a bending moment (or set of shear forces) across the femoral neck

26. Trabecular system The medial (or principal compressive) trabecular system The lateral (or principal tensile) trabecular system Accessory (or secondary) trabecular systems zone of weakness

27. The forces of HAT and the ground reaction force that act on the articular surfaces of the hip joint and on the femoral head and neck also act on the femoral shaft

28. Ranges of passive joint motion typical of the hip joint :- Flexion 90 ° with the knee extended and 120° when the knee is flexed Hip extension 10 ° to 20° Abducted 45° to 50° Adducted 20° to 30 ° Medial and lateral rotations of the hip the typical range is 42° to 50°

29. Hip Joint Musculature Movements Flexion : chiefly by psoas major, iliacus assisted by rectus femoris and sartorius Adductor longus assists in early flexion following full extension Extension : gluteus maximus and the hamstrings. Abduction : gluteus medius and minimus assisted by sartorius,tensor fasciae latae and piriformis Action is limited by adductor longus,pubofemoral ligament and medial band of ilio femoral ligament

30. Adduction : by adductor longus, adductor brevis and adductor fibers of adductor magnus Lateral rotation : piriformis, obturator internus and externus, superior and inferior gemelli and quadratus femoris assisted by the gluteus maximus Medial rotation : the anterior fibers of the gluteus medius and gluteus minimus, tensor fasciae latae Piriformis muscle was a lateral rotator at 0° of hip flexion but a medial rotator at 90° of hip flexion

31. MOTION OF PELVIS ON THE FEMUR Whenever the hip joint is weight-bearing, the femur is relatively fixed, and motion of the hip joint is produced by movement of the pelvis on the femur

32. Anterior and Posterior Pelvic Tilt Anterior and posterior pelvic tilts are motions of the entire pelvic ring in the sagittal plane around a coronal axis In the normally aligned pelvis, the anterior superior iliac spines (ASISs ) of the pelvis lie on a horizontal line with the posterior superior iliac spines and on a vertical line with the symphysis pubis Anterior and posterior tilting of the pelvis on the fixed femur produce hip flexion and extension

33. Hip joint extension through posterior tilting of the pelvis Hip flexion through anterior tilting of the pelvis

34. Lateral Pelvic Tilt Lateral pelvic tilt is a frontal plane motion of the entire pelvis around an anteroposterior axis In the normally aligned pelvis, a line through the anterior superior iliac spines is horizontal In lateral tilt of the pelvis in unilateral stance , one hip joint (e.g., the left hip joint) is the pivot point or axis for motion of the opposite side of the pelvis (e.g., the right side) as that side of the pelvis elevates (pelvic hike) or drops (pelvic drop).

35. If a person stands on the left limb and hikes the pelvis, the left hip joint is being abducted because the medial angle between the femur and a line through the anterior superior iliac spines increases. If a person stands on the left leg and drops the pelvis, the left hip joint will adduct because the medial angle formed by the femur and a line through the anterior superior iliac spines will decrease

36. Lateral Shift of the Pelvis With pelvic shift, the pelvis cannot hike; it can only drop . Because there is a closed chain between the two weight-bearing feet and the pelvis, both hip joints will move in the frontal plane in a predictable way as the pelvic tilt (or pelvic shift) occurs

37. Forward and Backward Pelvic Rotation Pelvic rotation is motion of the entire pelvic ring in the transverse plane around a vertical axis .

38. Forward (anterior) rotation of the pelvis occurs in unilateral stance when the side of the pelvis opposite to the weight-bearing hip joint moves anteriorly from the neutral position Forward rotation of the pelvis produces medial rotation of the weight-bearing hip joint

39. Backward (posterior) rotation of the pelvis occurs when the side of the pelvis opposite the weight-bearing hip moves posteriorly Backward rotation of the pelvis produces lateral rotation of the supporting hip joint

40. Pelvic Rotation in Gait In normal gait, the pelvis forwardly rotates around the weight-bearing hip while the other limb prepares for or is in swing Because this happens first on one leg and then on the other, it appears to the eye as if the pelvis is forwardly rotating and then backwardly rotating

41. Coordinated Motions of the Femur,Pelvis , and Lumbar Spine Pelvifemoral Motion When the femur, pelvis, and spine move in a coordinated manner to produce a larger ROM than is available to one segment alone, the hip joint is participating in what will predominantly be an open-chain motion termed pelvifemoral motion . Also been referred to as pelvifemoral rhythm

42. 2 types of response The open-chain response (the ability of each joint in the chain to move independently ) the head and trunk will follow the motion of the pelvis (moving the head through space ) Closed-Chain response the head will continue to remain relatively upright and vertical despite the pelvic motions

43. Moving the head and arms through space If the goal is to bend forward to bring the hands ( and head ) toward the floor, isolated flexion at the hip joints (anteriorly tilting the pelvis on the femurs) is generally insufficient to reach the ground

44. Moving the foot through space When a person is lying on the right side, the left foot may be moved through an arc of motion approaching 90 ° The abducting limb is in an open chain

45. A true open-chain response to isolated hip flexion would displace the head and trunk forward, with the line of gravity falling in front of the supporting feet In a functional closed chain, motion at the hip (one link in the chain) is accompanied by an essentially mandatory lumbar extension to maintain the head over the sacrum

46. Compensatory motions of the lumbar spine that accompany given motions of the pelvis and hip joint in a functional closed chain

47. HIP JOINT FORCES AND MUSCLE FUNCTION IN STANCE Bilateral Stance The line of gravity falls just posterior to the axis for flexion/extension of the hip joint In the frontal plane during bilateral stance, the superincumbent body weight is transmitted through the sacroiliac joints and pelvis to the right and left femoral heads joint axis of each hip lies at an equal distance from the line of gravity of HAT The gravitational moment arms for the right hip(DR ) and the left hip (DL) are equal

48. Because the body weight (W) on each femoral head is the same (WR = WL ), the magnitude of the gravitational torques around each hip must be identical WR X DR =WL X DL The gravitational torques on the right and left hips occur in opposite directions . The weight of the body acting around the right hip tends to drop the pelvis down on the left (right adduction moment), whereas the weight acting around the left hip tends to drop the pelvis down on the right (left adduction moment )

49. These two opposing gravitational moments of equal magnitude balance each other, and the pelvis is maintained in equilibrium in the frontal plane without the assistance of active muscles

50. Assuming that muscular forces are not required to maintain either sagittal or frontal plane stability at the hip joint in bilateral stance, the compression across each hip joint in bilateral stance should simply be half the superimposed body weight (or one third of HAT to each hip) In bilateral stance when both lower limbs bear at least some of the superimposed weight, the contralateral abductors and adductors may function as synergists to control the frontal plane motion of the pelvis.

51. Unilateral stance The left leg has been lifted from the ground and the full superimposed body weight (HAT) is being supported by the right hip joint. The weight of the non-weightbearing left limb that is hanging on the left side of the pelvis must be supported along with the weight of HAT by right hip joint. Of the one-third of the portion of body weight found in the lower extremities , the non-weightbearing limb must account for half of that, or one sixth of the full body weight

52. The magnitude of body weight (W) compressing the right hip joint in right unilateral stance, therefore, is Right hip joint compressionbody weight =[ 2/3 x W ] + [1/6 x W]= 5/6 x W

53. The force of gravity acting on HAT and the nonweightbearing left lower limb (HATLL) will create an adduction torque around the weight-bearing hip joint Gravity will attempt to drop the pelvis around the right weight-bearing hip joint axis. The abduction countertorque will have to be supplied by the hip abductor musculature The result will be joint compression or a joint reaction force that is a combination of both body weight and abductor muscular compression.

54. Compensatory Lateral Lean of the Trunk the compensatory lateral lean of the trunk toward the painful stance limb will swing the line of gravity closer to the hip joint, thereby reducing the gravitational moment arm It does reduce the gravitational torque

55. Use of a Cane Ipsilaterally Body wt passes mainly through cane Use of a Cane Contralaterally Cane assists the abductor muscles in providing counter torque

56. Pathological Gaits When a lateral trunk lean is seen during gait and is due to hip abductor muscle weakness, it is known as a gluteus medius gait If the same compensation is due to hip joint pain , it is known as an antalgic gait If lateral lean and pelvic drop occur during walking , the gait deviation is commonly referred to as a Trendelenburg gait

57. Femoroacetabular Impingement Cam impingement Pistolgrip deformity of the femoral neck

58. Pincer impingement caused by aberrations of the acetabulum

59. Reducing joint reaction force Reduced by Reducing the body weight-generated momentum By reducing body weight or reducing the body weight lever arm Seen in Trelendenburg gait(leaning towards the diseased hip)

60. Reducing the required hip abductor force Altering the neck-shaft angle through varus osteotomy/varus placement of the femoral stem Increasing offset or medialization of the socket Use of cane in contralateral hand

61. Biomechanics of total hip arthroplasty Stability and range of motion depends on : Head size Head-neck ratio and Implant design

62. Increasing the head diameter increases the jumping distance(i.e., the radius of the femoral head) Reduction of rates of revision for dislocation with increasing head size Primary arc of the joint

63. Increase in head-neck ratio increases this arc, improving the range of motion Head-neck ratio < 2:1 increase the risk of impingment leading to fixation failure, limited function and dislocation

64. Acetabular design features that can help increase the primary arc Semicaptive sockets that are greater than hemisphere reduce the primary arc and may have paradoxically adverse effect on stability

65. Acetabular hemispherical component If relatively small , stress transferred to the center If relatively large , stress transferred to the periphery Peripheral strains acting on a force vector perpendicular to the tangent at the rim stabilize the cup

66. Optimizing fixation and the low frictional torque arthroplasty CHARNLEY concept Shorten lever arm of the body weight by deepening the acetabulum and To lengthen the lever arm of the abductor mechanism by reattaching the osteotomized greater trochanter laterally Leading to decrease in moment produced by body weight there by reducing counterbalance force that the abductor mechanism must exert

67. Estimated load o femoral head in stance phase of gait is 3 times body weight When standing on 1 leg abductor muscles work done is 2.5 times body weight Load on femoral head during straight leg raising is 3 times body weight While lifting, running, jumping 10 times body weight

68. Abductor lever arm shortened in arthritis and also where head is lost or neck is shortened During the gait cycle, forces are directed against the prosthetic femoral head from a polar angle between 15-25 degrees anterior to the saggital plane of the prosthesis

69. Body’s center of gravity is posterior to the axis of the joint making the stem to deflect medially in coronal plane and posteriorly in saggital plane producing torsion of the stem As seen in arising from chair, ascending and descending stairs, lifting

70. Reducing the joint reaction force in total hip arthroplasty Lateralizing the femoral component by increasing the horizontal femoral offset Inadequate restoration of offset results in hip abductor insufficiency and soft tissue laxity Excessive femoral offset can also predispose to failure by overtightening of the hip, increasing the stress placed on the femoral fixation interface