Hip-Biomechanics-SRS-ppt faculty of physiotherapy.ppt

THE HIP COMPLEX BIOMECHANICS
1

Sreeraj
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HIP JOINT
• Diarthrodial joint with 3
DoF.
• Flexion/extension in
sagittal plane
• Abduction/adduction in
frontal plane
• Medial/lateral rotation in
transverse plane
• The primary function of
the hip joint is to support
the weight of the Head,
Arms, and Trunk (HAT)
both in static erect 2

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PROXIMAL ARTICULAR SURFACE
• The acetabulum (lunate
surface) is formed by the
union of the three bones
of the pelvis, with only the
upper horseshoe-shaped
area being articular.
• Full ossification of the
pelvis occurs between 20
and 25 years of age.
• The acetabulum is
positioned laterally with
an inferior and anterior
tilt. 3
Levangie PK, Norkin CC. Joint structure and function : a comprehensive analysis. 5th ed.
Philadelphia, Pa: F.A. Davis Company; 2011. p. 356–94.

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ACETABULAR ANTEVERSION
• Acetabular anteversion
angle describes the extent
to which the acetabulum
surrounds the femoral
head in the horizontal
plane.
• A value of 20 degrees is
typical.
• Excessive anteroversion
may lead to anterior joint
dislocation (especially
during excessive external
rotation). 4
Anterior edges
Posterior edges
Nick D, Jim N, Stefan K .Combined Acetabular and Femoral Version Angle in Normal
Male and Female Populations From CT Data. The British Editorial Society of Bone &
Joint Surgery. 2013 95(15): 168-168. doi: 10.1302/1358-
992X.95BSUPP_15.ISTA2012-168

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ACETABULAR TILT ANGLE
• Acetabular tilt is an index
of rotational position of
the acetabulum with
reference to the anterior
pelvic plane.
• tilted 20° in sagittal plane.
5
Fujii M, Nakashima Y, Sato T, Akiyama M, Iwamoto Y. Acetabular tilt correlates with acetabular
version and coverage in hip dysplasia. Clin Orthop Relat Res. 2012;470(10):2827–2835.
doi:10.1007/s11999-012-2370-z
ASIS
pubic
tubercles

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ACETABULAR INCLINATION ANGLE
• Defined as the angle
between the supero
inferior acetabular axis
and the longitudinal axis
in frontal plane.
• 50° is typical.
6
Superior edge
Inferior edge
Murray DW. The definition and measurement of acetabular orientation. J Bone
Joint Surg Br. 1993 Mar;75(2):228-32.

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CENTRE EDGE ANGLE
• Centre edge angle of
Wiberg: 25 – 300 normal
• <16°definite dysplasia
• 16° to 25° possible
dysplasia
• >40° may indicate Coxa
profunda
7
The CEA is formed between a vertical line
through the center of the femoral head and a
line connecting the center of the femoral head
and the bony edge of the acetabulum.
The acetabular labrum deepens the acetabulum.
Levangie PK, Norkin CC. Joint structure and function : a comprehensive
analysis. 5th ed. Philadelphia, Pa: F.A. Davis Company; 2011. p. 356–94.

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ACETABULAR LABRUM
1. A fibrocartilaginous rim
attached to the margin of
the acetabular socket.
2. Deepens the acetabular
socket.
3. With the transverse
acetabular ligament it
forms a complete circle.
• Nerve endings within the
labrum not only provide
proprioceptive feedback
but can also be a source
of pain.
8

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DISTAL ARTICULAR SURFACE
• The articular area of the
femoral head forms
approximately two thirds
of a sphere and is more
circular than the
acetabulum.
• The femoral neck is
angulated so that the
femoral head faces
medially, superiorly, and
anteriorly with respect to
the femoral shaft and
distal femoral condyles. 9

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ANGLE OF INCLINATION
10
• The axis of the femoral
head and neck forms an
angle with the axis of the
femoral shaft called the
angle of inclination.
• The angle of inclination of
the femur approximates
125° normally
• With a normal angle of
inclination, the greater
trochanter lies at the level
of the center of the
femoral head.
Coxa Valga Normal Coxa
Vara

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11
• Coxa valga leads to;
•  bending force across
femoral neck
•  in lateral trabecular
system
•  Abductor force
•  the contact of femoral
articular surface with
acetabulum.

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12
• Coxa vara leads to;
•  bending force along
femoral neck.
•  tensile stress on lateral
trabecular system
•  the predisposition
toward femoral neck
fracture.
•  chance of slipped
capital femoral epiphysis
in adolescence

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ANGLE OF TORSION
13

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ANGLE OF TORSION
• Anteversion: > 15-180
• Retroversion: < 15-180
14

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ANTEVERSION
In the supine position with the femoral
condyles parallel to the supporting
surface, the anteverted femoral head is
exposed anteriorly. Lateral rotation will
be limited, but medial rotation is
relatively excessive.
In standing, the anteverted femur tends
to medially rotate within the
acetabulum, resulting in medial
rotation of the femoral condyles in
relation to the plane of progression
leading to medial femoral torsion.
15

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ANTEVERSION
• Reduces hip joint stability because the femoral articular
surface is more exposed anteriorly.
• Excessive femoral anteversion can cause instability,
damage of the articular cartilage and acetabular labrum,
and eventually osteoarthritis.
• It can cause a decrease in the length of the abductor lever
arm resulting in additional abductor muscle force
requirement.
• May cause increased hip and knee adduction moments, an
intoeing gait and patellofemoral maltracking, with
resultant knee pain and arthritis.
16

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RETROVERSION
• Femoral retroversion can cause damage to the labrum and
articular cartilage, due to impingement between the
femoral neck and acetabulum leading to osteoarthritis of
the hip.
• An increased risk of slipped capital femoral epiphysis
• Susceptibility to a traumatic posterior hip dislocation.
• Residual, untreated femoral retroversion may be a reason
why hip preserving surgeries may fail, especially after the
arthroscopic treatment of hip impingement.
17

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COAPTATION OF THE ARTICULAR
SURFACES
• In the neutral or standing
position, the articular
surface of the femoral
head remains exposed
anteriorly and somewhat
superiorly.
• Not a true physiological
position of the hip joint.
(Kapandji)
• Maximum articular contact
of the head of the femur
with the acetabulum is
obtained when the femur 18
Levangie PK, Norkin CC

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SURFACES
• The stability of the hip joint is
assisted by gravity, in the
straight position by opposing
forces (ascending white arrow)
opposite to the body weight
(descending white arrow).
• The acetabular labrum, widens
and deepens the acetabulum
(black arrows), setting the stage for
a fibrous interlocking and
retaining system.
• The labrum retains the femoral
head with the help of the zona
orbicularis of the fibrous capsule
, which holds the femoral neck 19
https://en.wikipedia.org/wiki/Zona_orbicul
Kapandji AI

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SURFACES
• Atmospheric pressure
plays an important part in
securing the articular
coaptation of the hip joint.
• The acetabular fossa may
be important in setting up
a partial vacuum in the
joint so that atmospheric
pressure contributes to
stability by helping
maintain contact between
the femoral head and the
acetabulum. 20
Kapandji AI
acetabular fossa

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SURFACES
• The periarticular ligaments and
muscles are vital in
maintaining the coaptation of
the articular surfaces.
• Their functions are reciprocally
balanced. (Figure horizontal
section)
• Thus anteriorly the muscles are
very few (blue arrow) and the
ligaments (black arrows) are
strong, while posteriorly the
muscles (red arrow) predominate.
• This coordinated activity keeps
the femoral head (green arrow)
closely applied to the 21
Kapandji AI

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SURFACES
• Tensed ligaments in extension
are efficient in securing
coaptation.
• In flexion the ligaments are
slack, and the opposite
happens.
• This mechanism can be easily
understood using the
mechanical model, where
a. parallel strings run between
two wooden circles
b. When one circle is rotated
relative to the other, they
are brought closer together.
22
Kapandji AI
extension
flexion

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SURFACES
• The position of flexion is a
position of instability for
the hip joint because of
the slackness of the
ligaments.
• Flexion with adduction as
in legs crossed position is
easy to cause a posterior
dislocation of the hip joint
on a femoral impact.
• Dashboard injury
23
Kapandji AI

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THE ARTICULAR CAPSULE
• The capsule is attached
proximally to the entire
periphery of the
acetabulum beyond the
acetabular labrum.
• Fibers near the proximal
attachment forms a tight
ring just below the
femoral head known as
the zona orbicularis.
24

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THE ARTICULAR CAPSULE
• It is like a cylindrical sleeve helps
to unite the articular surfaces
• Made up of four types of fibres:
1. Longitudinal fibres, run parallel to
the axis of the cylinder
2. Oblique fibres, spiral around the
cylinder
3. Arcuate fibres, attached to the hip
bone and forming an arc whose
apex lies towards the middle of
the sleeve.
4. Circular fibres, which are
particularly abundant in the
middle of the capsule and form
the zona orbicularis (Weber's 25
Kapandji AI

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THE LIGAMENTS
• The hip joint is reinforced
by four ligaments, of
which three are
extracapsular and one
intracapsular.
• The extracapsular ligamen
ts are the iliofemoral,
pubofemoral,
and ischiofemoral
ligaments.
• The intracapsular ligament
, the ligamentum teres, is
attached to the acetabular 26
https://en.wikipedia.org/wiki/Hip#Ligaments

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THE LIGAMENTS
27
“Y” ligament of
Bigelow.

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THE LIGAMENTS
• During the change from
the quadruped to the
biped erect posture the
pelvis moved into a
position of extension
relative to the femur
• This made all the
ligaments coiled around
the femoral neck in the
same direction.
• Thus extension winds the
ligaments around the neck
more, tightening them, 28

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ROLE OF THE LIGAMENTS IN
EXTENSION
• During hip extension:
• all the ligaments become
taut especially the inferior
band of the iliofemoral
ligament.
• Thus responsible for
checking the posterior tilt
of the pelvis.
29
Example:
the iliac bone rotates backwards while the femur sta

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ROLE OF THE LIGAMENTS IN FLEXION
• During hip flexion:
• All the ligaments are
relaxed
• This relaxation of the
ligaments is one of the
factors responsible for the
instability of the hip in this
position.
30
Example:
the iliac bone tilts forward while the femur stays

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ROLE OF THE LIGAMENTS IN LATERAL
ROTATION
• During lateral rotation of
the hip:
• all the anterior ligaments
running horizontally, i.e.
the superior band of the
iliofemoral and
pubofemoral are taut.
• and slackening of the
ischio femoral ligament
31

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ROLE OF THE LIGAMENTS IN MEDIAL
ROTATION
• During medial rotation:
• all the anterior ligaments
running horizontally are
slackened,
• while the ischiofemoral
ligament becomes taut
• The vertical inferior band
of the iliofemoral ligament
limits medial rotation,
when the hip is in
extension.
32

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ADDUCTION
• The superior band is
tightened considerably,
• the inferior band only
slightly,
• pubofemoral ligament
relaxes.
• The ischiofemoral
ligament is stretched
during adduction
33
Ischiofemoral

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ABDUCTION
• The pubofemoral ligament
is tightened considerably
• The superior and the
inferior bands are relaxed.
• The ischiofemoral
ligament tenses up during
abduction.
34
Ischiofemoral

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ROLE OF THE LIGAMENTUM TERES
• A strong intrinsic stabilizer that resists joint subluxation
forces.
• It is most taut when the hip is in its least stable positions
i.e. flexion, adduction, and external rotation.
• Adduction is the only position where the ligament is really
under tension.
• And is lax in hip abduction and internal rotation.
35
Cerezal L, Kassarjian A, Canga A, et al. Anatomy,
Biomechanics, Imaging, and Management of
Ligamentum Teres Injuries. RadioGraphics.
2010;30(6):1637-1651. doi:10.1148/rg.306105516

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CAPSULOLIGAMENTOUS TENSION
• Hip joint extension, with slight abduction and medial
rotation, is the close-packed position for the hip joint.
• The capsuloligamentous tension at the hip joint is least
when the hip is in moderate flexion, slight abduction, and
midrotation.
• In this position, the normal intra-articular pressure is
minimized, and the capacity of the synovial capsule to
accommodate abnormal amounts of fluid is greatest.
• This is the position assumed by the hip when there is pain
arising from capsuloligamentous problems or from
excessive intra-articular pressure caused by extra fluid
(blood or synovial fluid) in the joint.
36

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STRUCTURAL ADAPTATIONS TO WEIGHT
BEARING - FEMUR
• The trabeculae are
calcified plates of tissue
within the cancellous bone
as a result of interaction
between mechanical
stresses and structural
adaptation created by the
transmission of forces
between bones.
• The trabeculae line up
along lines of stress and
form systems that
normally adapt to stress
requirements.
37

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BEARING - FEMUR
• The HAT loads the head of
the femur,
• The GRF comes up the
shaft of the femur,
• resulting in a moment arm
(MA)
• This bending moment
creates tensile stress on
the superior aspect of the
femoral neck and
compressive stress on the
inferior aspect.
38

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BEARING - FEMUR
• A complex set of adaptive
forces prevents the
rotation and resists the
shear forces that the force
couple causes;
• These forces are the
structural resistance of
two major and three minor
trabecular systems
• Two major are the medial
compressive and lateral
tensile trabecular systems.
39

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BEARING - FEMUR
• The zone of weakness is
an area in the femoral
neck in which the
trabeculae are relatively
thin and do not cross each
other.
• The zone of weakness of
the femoral neck is
particularly susceptible to
the bending forces across
the area and can fracture
as it has less
reinforcement and thus
more potential for failure.
40

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BEARING - FEMUR
• Changes in trabecular
patterns due to altered
angle.
• Coxa valga leads to more
compression trabeculae,
coxa vara to more tension
trabeculae.
41

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BEARING - FEMUR
• The forces of HAT and the
ground reaction force also act
on the femoral shaft.
• As the shaft of the femur lies
at an angle instead of vertical,
• loading on the oblique femur
results in bending stresses in
the shaft.
• The medial cortical bone of the
femoral shaft (diaphysis) must
resist compressive stresses,
whereas the lateral cortical
bone must resist tensile
stresses
42

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BEARING - ACETABULUM
• The primary weight-
bearing surface of the
acetabulum, or dome of
the acetabulum, is located
on the superior portion of
the lunate surface.
• In the normal hip, the
dome lies directly over the
center of rotation of the
femoral head.
• Peak contact pressures
during unilateral stance to
be located near the dome. 43

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BEARING - ACETABULUM
• Normal stress distribution
can be altered;
• with a lack of femoral
head coverage by the
acetabulum due to
decreased center edge
angle
• Excessive acetabular
anteversion
44
Coxa Valga Normal Coxa
Vara

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STRUCTURAL ADAPTATIONS TO WEIGHT BEARING –
ARTICULAR CARTILAGE
• The superior femoral head
receives compression from
• the dome in standing
• from the posterior
acetabulum in sitting
and
• the anterior acetabulum
in extension.
• Full loading of the hip
joint ensures congruence
and load distribution
between the larger
femoral head and the 45

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STRUCTURAL ADAPTATIONS TO WEIGHT BEARING –
ARTICULAR CARTILAGE
• Persisting incongruence of the acetabulum could result in;
• incomplete compression of the dome cartilage and,
• inadequate fluid exchange to maintain cartilage
nutrition.
• The articular cartilage is avascular, so it dependent on
compression & release forces to move nutrients through
the tissue;
• Both too little compression and excessive compression can
lead to compromise of the cartilage structure.
46

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MOTION OF THE FEMUR ON THE
ACETABULUM
• The motions of the hip joint are the movement of the
convex femoral head within the concavity of the
acetabulum as the femur moves through its three degrees
of freedom:
1. flexion/extension,
2. abduction/adduction, and
3. medial/lateral rotation.
• The femoral head will glide within the acetabulum in a
direction opposite to motion of the distal end of the
femur.
47

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ACETABULUM
• Flexion and extension of the femur occur as an almost
pure spin of the femoral head around a coronal axis.
• However, flexion and extension from other positions (e.g.,
in abduction or medial rotation) must include both
spinning and gliding of the articular surfaces, depending
on the combination of motions.
• The motions of abduction/adduction and medial/lateral
rotation must include both spinning and gliding of the
femoral head within the acetabulum
• The intra-articular motion occurs in a direction opposite
to motion of the distal end of the femur.
• For Example, The head spins posteriorly in flexion and48

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ACETABULUM
• Flexion of the hip is generally about 120° with the knee
flexed.
• It is limited to 90° with the knee extended due to passive
tension in the two joint hamstrings muscle group
• Hip extension is considered to have a range of 10 ° to 30°.
• When hip extension is combined with knee flexion, passive
tension in the two-joint rectus femoris muscle may limit
the movement.
49

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ACETABULUM
• The femur can be abducted 45° to 50° and adducted 20° to
30°.
• Abduction can be limited by the two-joint Gracilis muscle
• Adduction limited by the Tensor Fascia Lata (TFL) muscle
and its associated Iliotibial (IT) band.
• Medial and lateral rotation of the hip are usually measured
with the hip joint in 90° of flexion; the typical range is 42°
to 50°.
• Femoral anteversion is correlated with decreased range of
lateral rotation and increased range of medial rotation.
50

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ACETABULUM
• Normal gait on level ground requires at least the
• following hip joint ranges:
• 30° flexion,
• 10° extension,
• 5° of both abduction and adduction, and
• 5° of both medial and lateral rotation.
• Walking on uneven terrain or stairs increase the need for
joint range.
51

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MOTION OF THE PELVIS ON THE FEMUR
• The motion of the pelvis are the same three degrees of
freedom for the hip joint are accomplished by the pelvis
rather than by the femur.
• Anterior and posterior pelvic tilts are motions of the entire
pelvic ring in the sagittal plane around a coronal axis.
52
A. The pelvis in its normal position in
erect stance.
B. Posterior tilting of the pelvis moves
the symphysis pubis superiorly on
the fixed femur. The hip joint
extends.
C. In anterior tilting, the anterior
superior iliac spines move inferiorly
on the fixed femur. The hip joint
flexes.

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• 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.
A. Hiking of the pelvis around
the right hip joint results in
right hip abduction.
B. Dropping of the pelvis
around the right hip joint
53

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• Lateral Shift of the Pelvis
can also occur in bilateral
stance.
• When the pelvis is shifted
to the right in bilateral
stance, the right hip joint
adducted, and the left hip
joint abducted.
• To return to neutral
position in same stance
the right abductor and left
adductor muscles work
synergistically to shift the 54

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• Pelvic Rotation is motion of the entire pelvic ring in the
transverse plane around a vertical axis.
• Rotation can occur both in bilateral stance as well as in
single-limb support around the axis of the weight-bearing
hip joint.
55
A. Forward rotation of the pelvis
around the left hip joint results in
medial rotation of the left hip
joint.
B. Neutral position of the pelvis and
the left hip joint.
C. Backward rotation of the pelvis
around the left hip joint results in
lateral rotation of the left hip
joint.

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COORDINATED MOTIONS OF THE FEMUR, PELVIS,
AND LUMBAR SPINE
• When the pelvis moves on a relatively fixed femur, there
are two possible outcomes to consider.
1. Either the head and trunk will follow the motion of the
pelvis (moving the head through space) open chain
responses or
2. The head will continue to remain relatively upright and
vertical despite the pelvic motions, closed chain
responses.
57

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AND LUMBAR SPINE
• Pelvifemoral Motion is a coordinated movement of femur,
pelvis, and spine to produce a larger ROM than is available
to one segment alone.
• The lower, caudal end of the axial skeleton is firmly
attached to the pelvis by way of the sacroiliac joints.
Therefore, rotation of the pelvis over the femoral heads
typically changes the configuration of the lumbar spine.
This important kinematic relationship is known as
lumbopelvic rhythm
• Predominantly an open-chain motion but not exclusive.
• AIanalogous to scapulohumeral motion.
58

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AND LUMBAR SPINE
59

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AND LUMBAR SPINE
• Closed-Chain Hip Joint
Function is formed
because both ends of the
chain (both feet in this
example) are “fixed” and
movement at any one joint
in the chain invariably
involves movement at one
or more other links in the
chain.
60

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AND LUMBAR SPINE
PELVIC MOTION HIP JOINT MOTION LUMBAR SPINE MOTION
Anterior pelvic tilt Hip flexion Lumbar extension
Posterior pelvic tilt Hip extension Lumbar flexion
Lateral pelvic tilt (pelvic drop) Right hip adduction Right lateral flexion
Lateral pelvic tilt (pelvic hike) Right hip abduction Left lateral flexion
Forward rotation Right hip medial rotation
Rotation to the left (in closed
chain)
Backward rotation Right hip lateral rotation
Rotation to the right (in
closed chain)
61

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MUSCLES OF THE
HIP
• The line of pull of a
muscle is the long axis of
the muscle.
• The angle of pull is the
angle between the long
axis of the bone (lever
arm) and the line of pull of
the muscle.
• The angle of pull and
moment arm of the
muscle both change as the
joint goes through its
range of motion. 62
A lateral view shows the sagittal
plane line of force of several hip
muscles.

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MUSCLES OF THE HIP
• A muscle action describes the potential direction of
rotation of the joint following its activation
• A muscle torque describes the “strength” of the action.
• A muscle torque can be estimated by the product of the
muscle force (in Newtons) and the muscle’s associated
moment arm length (meters).
63

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HIP FLEXORS
• Primary
1. Iliopsoas
2. Rectus femoris
3. Sartorius
4. Tensor fasciae latae
5. Pectineus
• Secondary
1. Adductor brevis
2. Gracilis
3. Gluteus minimus
(anterior fibers)
64

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PELVIC-ON-FEMORAL HIP FLEXION
• The anterior pelvic tilt is
performed by a force-couple
between the hip flexors and
low-back extensor muscles.
• Any muscle capable of hip
flexion is equally capable of
tilting the pelvis anteriorly.
• Also note a consequent
increase in lordosis at the
lumbar spine.
• Greater lordosis increases the
compressive loads on the
lumbar apophyseal joints and
shear force at the lumbosacral
junction. 70

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FEMORAL-ON-PELVIC HIP FLEXION
• Open chain action.
• The synergistic action of one
representative abdominal
muscle (rectus abdominis) in
SLR.
A. With normal activation of the
abdominal muscles, the pelvis
is stabilized and prevented
from anterior tilting by the
downward pull of the hip
flexor muscles.
B. With reduced activation of the
abdominal muscles,
contraction of the hip flexor
muscles is shown producing a 71

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HIP ADDUCTORS
• Primary
1. Pectineus
2. Adductor longus
3. Gracilis
4. Adductor brevis
5. Adductor magnus
• Secondary
1. Biceps femoris (long
head)
2. Gluteus maximus (lower
fibers)
3. Quadratus femoris
72

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HIP ADDUCTORS
78
The anatomic organization and proximal attachments of the adductor muscle group.

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FRONTAL PLANE FUNCTION IN HIP
ADDUCTION
• The bilateral cooperative
action of selected
adductor muscles.
• Example: kicking a soccer
ball.
• The left adductor magnus
is shown actively
producing pelvic - on -
femoral adduction.
• Several right adductor
muscles are shown
actively producing femoral
- on - pelvic adduction 79
There is concentric activation of the
left adductor muscles and eccentric
activation of the left gluteus medius to
decelerate and control the motions.

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SAGITTAL PLANE FUNCTION IN HIP
ADDUCTION
• Adductor muscles are
considered flexors from the
extended position.
• When outside the 400 to 700
flexed position, the individual
adductor muscles regain
leverage as significant
extensors of the hip.
• From a hip position of near
extension, the line of force of
the adductor longus is well
anterior to the medial-lateral
axis of rotation.
• The adductor longus now has a
flexor moment arm and 80
These contrasting actions are based on the
change in line of force of the adductor longus,
relative to the medio lateral axis of rotation at
the hip.

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HIP INTERNAL ROTATORS
• Primary
Not applicable
• no muscle with any potential to
internally rotate the hip lies
even close to the horizontal
plane. From the anatomic
position, therefore, it is
difficult to assign any muscle
as a primary internal rotator of
the hip.
• Secondary
1. Gluteus minimus
(anterior fibers)
2. Gluteus medius (anterior
fibers)
4. Adductor longus
5. Adductor brevis
6. Pectineus
7. Piriformis
81

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• A superior view depicts the
horizontal plane line of force
of several muscles that cross
the hip.
• The external rotators are
indicated by solid lines and
• the internal rotators by
dashed lines.
82

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• The adductor muscles as
secondary internal rotators of the
hip.
A. Because of the anterior bowing of
the femoral shaft, a large segment
of the linea aspera runs anterior to
the longitudinal axis of rotation.
B. A superior view of the right hip
shows the horizontal line of force
of the adductor longus causes an
internal rotation torque by
producing a force that passes
anterior to the axis of rotation
83

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HIP EXTENSORS
• Primary
1. Gluteus maximus
head)
3. Semitendinosus
4. Semimembranosus
5. Adductor magnus
(posterior head)
• Secondary
1. Gluteus medius
(posterior fibers)
2. Adductor magnus
(anterior head)
84
With the hip flexed to at least about 70 degrees and beyond,
most adductors muscles except pectineus can assist with hip
extension.

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PELVIC-ON-FEMORAL HIP EXTENSION
PERFORMING A POSTERIOR PELVIC TILT
• The force couple between
representative hip
extensors and abdominal
muscles used to
posteriorly tilt the pelvis.
• Note the decreased
lordosis at the lumbar
spine.
• The extension at the hip
stretches the iliofemoral
ligament.
88

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CONTROLLING A FORWARD LEAN OF THE BODY
89
A. Slight forward lean of the
upper body displaces the
body weight force slightly
anterior to the medial-
lateral axis of rotation at
the hip.
• This slightly flexed
posture is restrained by
minimal activation from
the gluteus maximus and
hamstring muscles.

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CONTROLLING A FORWARD LEAN OF THE BODY
90
B. A more significant forward lean
displaces the body weight
force even farther anteriorly.
• The greater flexion of the hips
rotates the ischial tuberosities
posteriorly, thereby increasing
the hip extension moment arm
of the hamstrings.
• The gluteus maximus,
however, remains relatively
inactive in this position
• The taut line (with arrowhead
within the stretched hamstring
muscles) indicates the
increased passive tension.

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FEMORAL-ON-PELVIC HIP EXTENSION
• Consider the example of
climbing a steep hill
carrying a heavy pack.
• The flexed position
favours greater extension
torque generation from
the hip extensor muscles
and many of the adductor
muscles.
• The flexed position of the
right hip also imposes a
large external (flexion)
torque at the hip. 91
Activation is also required in low-back
extensor muscles to stabilize the position
of the pelvis.

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HIP ABDUCTORS
• Primary
1. Gluteus medius
2. Gluteus minimus
• Secondary
1. Piriformis
2. Sartorius
92

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HIP ABDUCTORS
• The gluteus medius and minimum have been likened to
the “rotator cuff” of the hip, with the supraspinatus and
subscapularis, respectively.
• Also analogous to the deltoid muscle of the glenohumeral
joint.
• the anterior fibers of the gluteus medius are active in hip
flexion and
• the posterior fibers function during extension.
• In the neutral hip,
• the posterior portion of the medius will produce a lateral
rotational moment and
• the middle and anterior portions have small medial
96

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HIP ABDUCTOR MECHANISM:
CONTROL OF FRONTAL PLANE STABILITY OF THE
PELVIS DURING WALKING
• During the stance phase the
hip abductor muscles have a
role in controlling the pelvis in
the frontal plane and the
horizontal plane.
• During the single-limb support
phase of gait the opposite leg
is off the ground and swinging
forward.
• Without adequate abduction
torque on the stance limb, the
pelvis and trunk may drop
uncontrollably toward the side
of the swinging limb. 97

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ROLE IN THE PRODUCTION OF COMPRESSION FORCE
AT THE HIP
• The counterclockwise torque
(solid circle) is the product of
the right hip abductor force
(HAF) times internal moment
arm (D)
• The clockwise torque (dashed
circle) is the product of body
weight (BW) times external
moment arm (D1).
• Because the system is assumed
to be in equilibrium, the
torques in the frontal plane are
equal in magnitude and
opposite in direction:
• HAF × D = BW × D1. 98
The illustration assumes that the pelvis and trunk
are in static (linear and rotary) equilibrium about the
right hip.

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ROLE IN THE PRODUCTION OF COMPRESSION FORCE
AT THE HIP
• Note that the internal moment
arm (D) used by the hip abductor
muscles is about half the length
of the external moment arm (D1)
used by body weight.
• So, hip abductor muscles must
produce a force twice that of body
weight in order to achieve
stability during single-limb
support.
• This downward force is
counteracted by a joint reaction
force (JRF) of equal magnitude
oriented in nearly the opposite
direction.
• The JRF angulation is strongly 99

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HIP EXTERNAL ROTATORS
• Primary
1. Gluteus maximus
2. Piriformis
3. Obturator internus
4. Gemellus superior
5. Gemellus inferior
6. Quadratus femoris
• Secondary
1. Gluteus medius
(posterior fibers)
2. Gluteus minimus
(posterior fibers)
3. Obturator externus
4. Sartorius
head)
100

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101

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102

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PELVIC-ON-FEMORAL HIP EXTERNAL
ROTATORS
• With the right lower
extremity firmly in contact
with the ground,
contraction of the right
external rotators
accelerates the anterior
side of the pelvis and
attached trunk to the left -
contralateral to the fixed
femur.
• This action of planting a
foot and “cutting” to the
opposite side is the
natural way to abruptly
103

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HIP ROTATORS
• The piriformis, reportedly an external rotator in full
extension but an internal rotator at 90° or more of flexion.
• Restrictions in the extensibility of this muscle are typically
described as limiting passive hip internal rotation, and
possibly compressing the underlying sciatic nerve.
• A traditional method for stretching a tight piriformis is to
combine full flexion and external rotation of the hip,
typically performed with the knee flexed.
104

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HIP JOINT FORCES AND MUSCLE FUNCTION
IN STANCE
BILATERAL STANCE
• In erect bilateral stance,
• both hips are in neutral and
• weight is evenly distributed between both legs.
• The line of gravity falls just posterior to the axis for
flexion/extension of the hip joint.
• The posterior location of the line of gravity creates an
extension moment of force around the hip which is largely
checked by passive tension in the hip joint
capsuloligamentous structures and activity of hip flexors.
• In the frontal plane, the body weight is transmitted
through the sacroiliac joints and pelvis to the right and left
femoral heads. 105

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IN STANCE
BILATERAL STANCE
• DR & DL : the gravitational
moment arms
• WR & WL : body weight
• Because WR = WL
• Magnitude of gravitational
torque around hip is:
WR X DR = WL X DL
• Total hip joint
compression = 4/6 X body
weight
106

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IN STANCE
BILATERAL STANCE
• In normal B/L stance,
assuming no muscular
forces maintain either
sagittal or frontal plane
stability at the hip joint,
• the compression across
each hip joint should be
half the superimposed
body weight
• or one third of HAT to
each hip.
• Example: Assuming a
body weight of 84 Kg.
• The weight of HAT is 4/6
body weight.
• 84 X 4/6 = 56 Kg.
• Each hip receives 56/2 =
28 Kg.
HAT: Head Arm Trunk
107

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IN STANCE
UNILATERAL STANCE
• Full superimposed body
weight (HAT) is being
supported by the right hip
joint.
• The weight of the non-
weight bearing left limb
must now be supported
along with the weight of
HAT.
• The magnitude of body
weight (W) compressing
the right hip joint is [4/6 X
W] + [1/6 X W] 108

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IN STANCE
UNILATERAL STANCE
Example: Assuming a body weight of 84 Kg.
• The magnitude of body weight (W) compressing the right
hip joint is [4/6 X W] + [1/6 X W]
• 4/6 X 84 + 1/6 X 84
• 56 + 14 = 70
• So right hip joint compression body weight is 70 Kg
• Now the hip joint in unilateral stance being compressed by
body weight (gravity) concomitantly creating a torque
around the hip joint.
109

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IN STANCE
UNILATERAL STANCE
• The force of gravity acting on HAT and the non weight
bearing left lower limb (HATLL) will create an adduction
torque around the weight-bearing hip joint ( drop of non
weight bearing limb) and an abduction counter torque 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.
110

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IN STANCE
UNILATERAL STANCE
Example: Assuming a body weight
of 84 Kg.
• So right hip joint
compression body weight is 70
Kg
• Add./LOG MA is 10 cm =
0.1m
• Abd. MA is 5 cm = 0.05 m
• HATLL torque add. = 70 X
0.1 = 7 Kg
• So torque abd. = Torque
Add./ Abd. MA = 7/0.05 =
140 Kg
• The total hip joint
compression, or joint reaction
111

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IN STANCE COMPENSATORY LATERAL LEAN OF
THE TRUNK
• When the trunk is laterally
flexed toward the stance
limb, the moment arm of
HATLL is substantially
reduced.
• 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 112

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IN STANCE COMPENSATORY LATERAL LEAN OF
THE TRUNK
Example: Assuming a body weight
of 84 Kg.
• So right hip joint compression
body weight is 70 Kg
• Add./LOG MA is 2.5 cm =
0.025m
• Abd. MA is 5 cm = 0.05 m
• HATLL torque add. = 70 X
0.025 = 1.75 Kg
• So torque abd. = Torque
Add./ Abd. MA = 1.75/0.05 =
35 Kg
• The total hip joint
compression, or joint reaction
force is abd. torque + HATLL 113

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IN STANCE
USE OF A CANE IPSILATERALLY
• Pushing downward on a cane held in the hand on the side
of pain or weakness should reduce the superimposed body
weight by the amount of downward thrust;
• that is, some of the weight of HATLL would follow the arm
to the cane, rather than arriving on the sacrum and the
weight-bearing hip joint.
• The proportion of body weight that passes through the
cane will not pass through the hip joint and will not create
an adduction torque around the supporting hip joint.
114

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IN STANCE
USE OF A CANE IPSILATERALLY
• If 84 kg push down on the kane with 15% BW = 84 X 0.15 = 12.6
will pass through kane
• So the magnitude of HATLL is 70 – 12.6 = 57.4
• So right hip joint compression body weight is 57.4 Kg
• Add./LOG MA is 10 cm = 0.1m
• Abd. MA is 5 cm = 0.05 m
• HATLL torque add. = 57.4 X 0.1 = 5.74 Kg
• So torque abd. = Torque Add./ Abd. MA = 5.74/0.05 = 114 Kg
• The total hip joint compression, or joint reaction force is abd. torque
+ HATLL W
• i.e. 114 + 57.4 = 172.2 Kg
115

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IN STANCE
USE OF A CANE CONTRALATERALLY
• When a cane is placed in
the hand opposite the
painful supporting hip, the
weight passing through
the right hip is reduced.
• Activation of the left
latissimus dorsi provides a
counter torque to that of
HATLL and diminishes the
need for a contraction of
the right hip abductors.
• In this example the MA of
the cane is estimated to 116

Sreeraj
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IN STANCE
USE OF A CANE CONTRALATERALLY
• If 84 kg push down on the kane with 15% BW = 84 X 0.15 = 12.6
will pass through kane
• So the magnitude of HATLL is 70 – 12.6 = 57.4
• So right hip joint compression body weight is 57.4 Kg
• Adduction/LOG MA is 10 cm = 0.1m
• Abduction MA is 50 cm = 0.5 m
• HATLL torque add. = 57.4 X 0.1 = 5.74 Kg
• Cane torque = 12.6 X 0.5 = 6.3
• If assume that the gravitational adduction torque and the counter
torque provided by the cane offset each other there would be no
need for hip abductor muscle force
• The total hip joint compression, or joint reaction force is abd.
torque + HATLL W 117

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• https://hipandkneebook.c
om/biomechanics
118

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1. Martin RL, Kivlan B. The Hip Complex. In: Levangie PK, Norkin CC, editors. Joint
structure and function : a comprehensive analysis. 5th ed. Philadelphia, Pa: F.A.
Davis Company; 2011. p. 356–94.
2. Kapandji AI. The Hip. In: Physiology of the Joints: Volume 2 Lower Limb. 6th ed.
Edinburgh ; New York: Churchill Livingstone/Elsevier; 2011. p. 2–65.
3. Uritani D, Fukumoto T. Differences of Isometric Internal and External Hip Rotation
Torques among Three Different Hip Flexion Positions. Journal of Physical Therapy
Science. 2012;24(9):863-865. doi:10.1589/jpts.24.863
4. Neumann DA. Kinesiology of the Hip: A Focus on Muscular Actions. Journal of
Orthopaedic & Sports Physical Therapy. 2010 Feb;40(2):82–94.
5. Therapeutic Exercise for Musculoskeletal Injuries [Internet]. [cited 2020 Feb 4].
Available from:
https://humankinetics.com/AcuCustom/Sitename/DAM/153/Houglum_78-79.pdf
6. Lippert L. Chapter 17 Hip. In: Clinical kinesiology and anatomy. 4th ed.
Philadelphia: F.A. Davis Company; 2006. p. 233–49.
119

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