1) The hip joint is a ball-and-socket joint that allows flexion, extension, abduction, adduction, and rotation. It supports the weight of the head, arms, and trunk. 2) The hip joint is made up of the femoral head articulating with the acetabulum. Several ligaments and the acetabular labrum provide stability to the joint. The angle of the femoral neck and torsion of the femur also affect biomechanics. 3) During standing and walking, forces from the body weight and ground reaction force act on the hip joint and femoral neck. A system of trabeculae in the femoral neck adapt to these forces. Muscles around the

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:
1. flexion/extension in the sagittal plane
2. abduction/adduction in the frontal plane
3. 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
ofovea or fovea capitis
oligament 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
Angle 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. • An 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

19. 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

20. • 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

21. 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

23. 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

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

25. HIP JOINT LIGAMENTS
• Iliofemoral ligament(Y ligament of Bigelow)
• Pubofemoral ligament
• Ischiofemoral ligament

27. STRUCTURALADAPTATIONS 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.

28. • 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

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

30. • 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

31. • 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°

32. 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

33. 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

34. 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

35. 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

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

37. 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).

38. • 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

39. 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

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

41. • 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

42. • 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

43. 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

44. 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

45.  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

46. 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

47. 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

48. • 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

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

50. 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

51. • 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)

52. • 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

53. • 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.

54. 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

55. • 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

56. • 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.

57. 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

58. 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

59. 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

60. Femoroacetabular
Impingement
Cam impingement
 Pistolgrip deformity of the
femoral neck

62. Pincer impingement
 caused by aberrations of
the acetabulum

63. 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)

64. 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

65. Biomechanics of total hip arthroplasty
Stability and range of
motion depends on :
1. Head size
2. Head-neck ratio and
3. Implant design

66. 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

67. 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

68. 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

69. Acetabular hemispherical
component
1. If relatively small , stress
transferred to the center
2. 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

70. 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

72. 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

73. 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

74. 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

75. 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