Hip joint (biomechanics)

1. HIP JOINT
The weight bearing joint, in which there is articulation
of head of the femur and the acetabulum of pelvic
bone.
MUSCULATURE OF HIP
JOINT:
Like all other joints hip joint is also supported by muscles. They cause the movement of the
joint and give support to the joint.
Different muscles work in different way in different positions.
Like the adductor muscles maybe hip flexors in neutral position but maybe hip extensors when
the hip is flexed
MOVEMENTS AT HIP JOINT:
Hip abduction/adduction
Hip flexion/extension
Hip medial/lateral rotation
HIP MUSCLES:
Flexors
Extensors
Abductors
Adductors
Medial rotators
Lateral rotators

2. FLEXORS:

1) Sarotrius 2)ilopsoas 3) Rectus femoris
ILIACUS MUCLCE:
ORIGIN:Iliac fossa of the hip bone
INSERTION:With psoas into the lessor
trochanter of the femur.
PSOAS MUSCLE:
ORIGION:Transverse process, bodies and
intervertebral discs of the 12
th
thoracic and
five lumber vertebrae.
Insertion:Withiliacus into lessor
trochanter of the fumer.
COMBINE ACTION OF ILIACUS AND PSOAS MUCLE:
Flexes thigh on trunk,if thigh is fixed it flexes the trunk on the thigh as in sitting up from
lying down.
This muscle combine cause hip flexion and extrernal rotation.
Unilateral action of these mucle cause trunk lateral roation.
Bilateral action of these muclse cause raising of the trunk from the fully supine position.
Iliacus muscle cause flexion and psoas mucles cause flexion and lateral roation of lumber
spine.
RECTUR FEMORIS:
ORIGION:
STRAIGHT HEAD:Anteriorintferior iliac spine.

3. REFLECTED HEAD:Ilium above acetabulum.
INSERTION:Quadriceps tendon into patella, then via ligamentum patella into tubercle of
tibia.
ACTION:
Cause function on both hip joint and on knee.
It cause hip flexion and knew extension.
ACTIVE INSUFFICIENCY:
During hip flexion and knee extension,a point come where no more flexion of hi joint
occurs,due to the active insufficiency of recturfemoris muscle.
At the same time the action is stopped by the hamstring muscle because of its passive
insuffiency.
Passive insufficiency is actually the pint where no more extension of a muscle can occur.
SARTORIUS:
Anterior superior iliacspine.
ORIGION:Anterior superior iliacspine.
INSERTION:Upper medial surface of shaft of tibia.

ACTION:
This muscle has so many functions at hip and knee joint.
The tailor sitting/ cross sitting is actually due to this muscle
During cross sittion there is flexion at hip and knew joint
At the same time lateral rotation of thigh at hip joint and medial roation of leg at knew
joint.

4. TENSOR FASCIA LATA:
ORIGION:Iliac crest
INSERTION:Iliotibialtract,,it is the
thickening of the fascia lata on the laterally
ACTION:
This mucle cause three main functions,
Flexion of thigh at hip joint, abduction and
medially rotation.
The Iliotibial tract and tensor fascia lata are
stretchable, they assist in tensile force and
prevent femur from fracturing, as we know
bone can bear compressive for rather than
tensile.

SECONDARY HIP FLEXORS:
Pectinius, adductor longus, adductor magnus
and gracilis.
These muscles cause 40-50% flexion of hip
joint.
Gracilis is active when there is hip flexion
and knee extension.
ADDUCTORS:
Adductors of the hip joint are:
Gracilis,adductormagnus,adductorbrevis,adductorlongus.
main action of these mucles is :
they laterally rotates thigh at hip joint and assists in lateral rotation.

5. Adductor longus,brevis and posterior adductor
magnus muscles have only small movement
arms for medial rotation
Gracilis and anterior adductor magnus have
smaller moment arm for lateral rotation.
Gracilismuscle also cause knee flexion.
EXTENSORS:
The main extensors of the hip joint are:
Gluteus maximus and hamstring muscles
GLUTEUS MSUCLE:
This is the longest mescle with mass 12.5% of total body muscles.
It is the main extensor of the hip joint.
It is the main mucles which can bear weight more then human body
Its moment arm is more than both posterior adductor magunus muscle and that of gracilis.
HAMSTRINGS:
There are three two joint mucles in hamstrings:
Semitendinosus,semimembranosus and biceps femoris.
They assist up to 35% for hip extension when the hip is flexed.
These mucles also cause knee flexion that’s why they are considered very important.
Their combine strength is yet not more than gluteus maximus.
ABDUCTORS:
The main abductors are:
Gluteus medius and gluteus minimus

6. Glutiusmedius:
like the deltoid muscle it has three
man prats;
anterioir ,posterior and middle
the anterior fibers are active during
hip flexion and posterior function in
hip extension.
In neutral position, posterior fibers
cause lateral rotation while anterioir
and middle cause medial rotation.
All the mucles fibers of gluteus
medius combine cause abduction of
hip joint.
GLUTIUS MINIMUS:
This mucle cause main abduction but also play role in hip flexion.
It can cause medial rotation.
It combines with gluteus medius and cause abduction of hip.
Lateral rotators:
These include:
Superior gemilus,interiorgemilus , obturatorexternus and internus , piriforimis and
quadratusfemoris.
Piriforimis has a large moment arm,it cause lateral rotation at 0 degree flexion but cause medial
rotation at 90 degree flexion.
The obturatorexternus and the quadratusfemoris do not dimish their lateral rotation for
flexion, they have comparative small moment arm.
All these muscles like the rotator cuff are considered the joint compressors because their
combine moment arm is parallel to the head and neck of the femur.

7. MEDIAL ROTATORS:
There are no primary muscles for medial rotation of hip joint.
Medial rotation can be caused by secondary muscles like:
Gluteus medius,minimus and tensor fascia lata.
Medial rotation can occur three times more in flexion than in extension.