bio mechanics of the hip

Biomechanics Biomechanics of of

the Hipthe Hip

Pelvic Girdle

•The two hip bones plus the

sacrum

•Can be rotated forward,

backward, and laterally to

optimize positioning of the

hip joint

Obturator foramen

ischium

ilium

pubis

sacrum

acetabulum

Pelvic girdle

Pelvic Bone

Pelvic Bone

Anterior Tilt

• Forward tilting

and downward

movement of

the pelvis

• Occurs when

the hip extends

Posterior Tilt

• Tilting of the

pelvis

posteriorly

• Occurs when the

hip flexes

Lateral Tilt• Tilting of the pelvis from

neutral position to the right or

left

• Lateral tilt tends to occur

naturally when you support

your weight on your leg

• This allows you raise your

opposite leg enough to swing

through during gait

Pelvic Rotation• Rotation of the pelvis

defined by the direction in

which the anterior aspect

of the pelvis moves

• Occurs naturally during

unilateral leg movements

(walking)

– As the right leg swings

forward during gait the

pelvis rotates left

Hip Joint

• Consists of – Pelvic bone

•Acetabulum– Femur

Acetabulum

Acetabulum

Femur

Femur

Femur

Structure of the Hip

• A ball and socket joint in which the head of the femur articulates with the concave acetabulum

• The hip is more stable than the shoulder – Bone structure – The number and strength of the

muscles and ligaments crossing the joint

Acetabular Labrum

• Acetabulum is not a complete circle, open inferiorly

• This opening is closed by the transverse ligament

Head Ligament

• Head of femur attached to inside of acetabulum by ligamentum teres

Capsule

Ligaments

• Iliofemoral ligament or the “Y ligament of Bigelo”– Triangular in shape– Supports hip anteriorly, resists extension,

internal rotation and some external rotation

• Pubofemoral– Runs from the superior pubic ramus and the

acetabular rim, to just above lesser trochanter

– Resists abduction with some resistance to external rotation

Ligaments

• Ischiofemoral ligament– From the ischium to the posterior neck

of the femur – is directed upwards and laterally

– Resists adduction and internal rotation– All three loose during flexion

Ligaments

Anterior view

Posterior view

Vascular

Vascular

Lumbar Division

Hip Goniometry

• Flexion/Extension– 125-140 (with knees flexed)/0/10-

20– 90 (with knees extended)/0/10-20

• Abduction/Adduction– 45/0/20-30

• Internal Rotation/External Rotation– 35-45/0/40-50

Hip Movements

• Hip Flexion

• Flexion– Psoas major– Iliacus

– Assisted by:•Pectineus

•Rectus femoris

•Sartorius

•Tensor fascia latae

Hip Movements

Psoas major

Iliacus

Pectineus

Rectus femoris

Sartorious

Tensor fascia latae

Iliotibial band

• Hip Extension

Hip Movements

• Extension

– Gluteus Maximus– Hamstrings

•Biceps Femoris

•Semimembranosus

•Semitendinosus

Hip Movements

Gluteus maximus

• Hip Abduction

Hip Movements

• Abduction

– Gluteus Medius

– Assisted By:• Gulteus Minimus

Hip Movements

Gluteus medius

Gluteus minimus

• Hip Adduction

Hip Movements

• Adduction

– Adductor Magnus

– Adductor Longus

– Adductor Brevis

– Assisted By:•Gracilis

Hip Movements

Gracilis

• Internal/Medial

Rotation

– Gulteus

Minimus

– Tensor fascia

latae

Hip Movements

• External/Lateral

Rotation

– Obturator Externus

– Obturator Internus

– Quadratus femoris

– Piriformis

Hip Movements

Obturator Externus

Obturator Internus

Piriformis

Quadratus femoris

Angle of Inclination

Coxa Vara• The angle of inclination is less than

125 degrees • This shortens the limb• Increases the effectiveness of the

abductors• Reduces the load on the femoral

head • Increases the load on the femoral

neck

Coxa Valga

• The angle of inclination is greater than

125 degrees

• This lengthens the limb

• Reduces the effectiveness of the

abductors

• Increases the load on the femoral head

• Reduces the load on the femoral neck

Hip Angles

• 14-15 degrees

• Moves CM more

directly over

base of support

Anteversion• The angle of the

femoral neck in the

transverse plane

• Normally the femoral

neck is rotated

anteriorly 12 to 14

degrees with respect

to the femur

Excessive Anteversion• Excessive anteversion

beyond 14 degrees causes the head of the femur become uncovered

• In order to keep the head of the femur within the acetabulum a person must internally rotate the femur

Retroversion

• The angle of anteversion

is reversed so that it

moves posteriorly

• This condition causes

the person to externally

rotate the femur

Loads on the Hip• During swing phase of walking:

– Compression on hip approx. same as body weight (due to muscle tension)

• Increases with hard-soled shoes• Increases with gait increases (both

support and swing phase)• Body weight, impact forces

translated upward thru skeleton from feet and muscle tension contribute to compressive load on hip

600 N

250 N

Using A Walking Stick

Using a walking stick how it reduces JRF

• In equilibrium sum of moments = 0

• Without stick

M x A = W x B

M = (W x B)/A

Using a walking stick how it reduces JRF

Using a walking stick how it reduces JRF

• With sitck(M x A)+(Ws x C) = W x BM = [(W x B)-(Ws x C)]/A

• So the force required by the abductors M is smaller if a stick is used

• The bigger C is, the smaller M is therefore a walking stick in the hand furthest away from the hip is most effective

Using a walking stick how it reduces JRF

• In equilibrium, the sum of the forces in the Y plane = 0

• Without stick

JRF sin   = M + W

• With stick

JRF sin + Ws = M +W

JRF sin = M + W - Ws

Using a walking stick how it reduces JRF

• Therefore JRF is less when a

walking stick is used. Not only is M

force smaller, but the upward force

exerted by the stick reduces the

JRF further

Using a walking stick how it reduces JRF

W

opposite

hurtleg

W

same

hurtleg