Functional Anatomy: Hip

Osteology for hips

Innominate Ossification

full ossification occurs between 20-25 years of age

until ossification occurs, connected via cartilaginous union

Pelvis → lateral view → acetabulum

acetabulum fossa

faces: lateral, anterior, and inferior 

does not articulate with femoral head 

acetabulum articulating surface

horseshoe shape located anteriorly, superiorly, and posteriorly

• articulates with femoral head

acetabular notch

located anterior-inferiorly

ligamentum teres origin

bridged by transverse acetabular ligament

contents of acetabulum

• lunate surface: hyaline cartilage, thick superior and anterior (based on WB)

• fat pad

• ligamentum teres

• transverse acetabular ligament: spans acetabular notch and part of labrum, connects lunate surfaces

• acetabular labrum

acetabular labrum

• fibrocartilage

• deepends socket and increase concavity

• negative articular pressure

• increases stability

• nerve endings: proprioception (joint stability and balance) and pain

clinical relevance: labral tear

when labrum is compromised → friction stresses increases → articular cartilage deterioration → hip osteoarthritis

arthrology

• diarthrodial ball and socket joint

• primary function: support the weight of the head, arms, trunk in static erect posture and dynamic postures

  • primary functions are in weight bearing (compared to shoulder)

angle of the hip

acetabular angles: center edge angle and acetabular version

femoral angles: angle of inclination and femoral neck torsion

center edge angle 

formed by 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 

• definite dysplasia <16 degrees

• possible (borderline) dysplasia 16-25 degrees

• normal >25 degrees 

• excessive > 40 degrees 

femoral neck coverage

acetabular dysplasia: shallow acetabulum that results in a lack of femoral head coverage = instability (less angle = less stability)

coxa profunda: acetabulum excessively covers the femoral head (excessive angle = impingment)

angle of acetabular version

known as the acetabular anteversion/retroversion angle

amount of anterior or posterior orientation in the transverse plane

Normal ~20 degrees anteversion

>20 degrees is anterversion, <20 is retroversion

femoral neck coverage acetabular anteversion

acetabulum is positioned excessively anteriorly in the transverse plane → can lead to instability

femoral neck coverage acetabular retroversion

acetabulum is positioned posteriorly in the transverse plane → can lead to over coverage of the femoral head/neck (impingement)

femur

head, neck, trochanters (greater/lesser), lateral epicondyle and medial epicondyle

femur from medial view

fovea (ligementum teres attachment; not covered in hyaline cartilage) and anterior aspect of head exposed

femoral neck

angulated so that the femoral head faces medially, superiorly, and anteriorly with respect to the femoral shaft and condyles 

angles of the femur

torsion of the femur:

• twist between shaft and neck in the transverse plane

• neck projects anterior to a M/L axis through the femoral condyles

• birth 30=40 degrees

• by skeletal maturity, normal angle: 15-18 degrees

Femoral anterversion

-angle of torsion >15-20 degrees

-reduces hip joint stability

-more exposed anteriorly

-may lead to subsequent labral pathology

-to improve congruency → medial rotation of the femur

-alter knee biomechanics

-may lead to lateral tibial torsion

-hip ROM: increased medial rotation, decreased lateral rotation

-hip ER will be limited with hard end feel (DO NOT TRY AND STRETCH)

Femoral retroversion

-increases hip stability but can lead to impingement

-impingement can lead to subsequent labral pathology

-to improve congruency → lateral rotation of the femur 

-alter knee biomechanics

-hip ROM: excessive hip ER and limited IR 

-hip IR will be limited with hard end feel (DO NOT TRY AND STRETCH) 

clinical implications of abnormal torsions

varus

an angulation of a distal segment towards the midline of the body relative to the normal ranges

valgus

an angulation of a distal segment away from the midline of the body relative to the normal ranges 

angle of inclination

-angle between the femoral neck and femoral shaft in the frontal plane

-adult normal ~125 degrees

-decreased angle = coxa vara <125

-increased angle = coxa valga >125 degrees

development and the angle of inclination

Clinical implications of coxa valga 

-angle of inclination is > normal 

-decreases abduction moment arm leading functionally weakened hip and increased joint reaction force 

-decreased stability due to lessened coverage of the femoral articular surface with the acetabulum 

-prediposes to hip dislocation 

Barlow and Ortolani tests

LE chain effects of coxa valga

-less stability

-shallow acetabulum

-abducted hip

-genu varum at the knee

-supination of the foot

-longer limb

-normal at birth

clinical implications of coxa vara

-increased hip joint stability

-increases moment arm of abductors (functionally stronger hip) reduces joint reaction force

-increase bending moment across femoral neck predisposition for (slipped capital femoral epiphysis or femoral neck fracture)

slipped capital femoral epiphysis

-typical demographics

• male > female

• obesity

• african americans

• northeast US

-associated with: hormonal abnormalities, specifically thyoid

LE Chain effect of Coxa Vara

increased shear force across the femoral neck, adducted hip, valgus knee, pronation at foot, shorter limb 

Hip capsule

• thick and strong and reinforced by strong ligaments

• dense, inelastic and fibrous and encloses the entire joint

• attaches to the periphery of the acetabulum blending with the labrum medially with multiple lateral attachments

• thickest anterior & superior

• thinnest posterior & inferior

• -lined with synovial membrane

hip proximal capsule

attaches to periosteum proximal to acetabular rim and acetabular labrum

hip distal capsule

surrounds femoral neck (intra-capsular) but not the trochanters (extra-capsular) 

-oblique fibers form collar-like structure around femoral neck known as zone orbicularis preventing distraction of the femoral head 

ligaments of the hip 2

Hip joint capsule reinforcing ligaments:

• anterior: iliofemoral ligament and pubofemoral ligament

• posterior: ischiofemoral ligament

ligamentum teres

iliofemoral ligament (Y ligament of bigelow)

O&I: AIIS to intertrochanteric line

superior band fibers are the strongest in the hip

limits hip extension, ER

superior fibers may be taut in adduction and inferior fibers taut in abduction

pubofemoral

O&I: anterior and inferior rim of the acetabulum and adjacent parts of the superior pubic ramus then cross joint to blend with medial band of iliofemoral ligament 

-limits hip abduction, extension, ER 

Ischiofemoral ligament

O&I: posterior acetabular rim to inner surface of the greater trochanter

-limits hip extension and IR

ligamentum teres

O&I: from acetabular notch to the fovea

intra-articular but extrasynovial

conduit for secondary blood supply to the femoral head

recent studies show it provides some stability

-limits hip IR and ER (when hip is >90 deg flexion)

ligaments of the hip 

anterior, posterior, intra-capsular 

general concept: ligaments LAX in flexion and TAUT in extension → capsular and ligamentous twist 

femoral neck blood supply

femoral head is most commonly supplied by the medial femoral circumflex artery

minimal to no secondary arterial supply to femoral head

increases femoral head risk of avascular necrosis

legg-calve-perthes disease

Legg-Calve-Perthes Disease

collapse of the femoral head due to loss of blood supply during childhood

Hip flexion ROM 

~125 degrees

hip extension ROM

~10-30 deg

hip abduction ROM

~45 deg

hip adduction ROM

~20-30 deg

Hip IR ROM

~45 deg

Hip ER ROM 

~45 deg

Closed Pack Position of the Hip

full extension of the hip with internal rotation and abduction

• twist fibers within the capsular ligaments to most taut positon

• not associated with the position of maximum joint congruency

• most congruently in 90 degrees of flexion, abduction, and external rotation

Hip joint most congruent

90 degrees of flexion, abduction, and external rotation

Open pack position of the hip 

30 degrees flexion, 30 degree abduction, and slight ER 

open chain arthrokinematics

femur moving on the pelvis

convex on concave rule

roll and glide opposite

open chain hip arthrokinematics flexion

femoral head “SPINS”

-clinically: rolls anterior, glides post and rolls superior, glides inferior open chain hip arthrokinematics (sagittal plane)

open chain hip arthrokinematics extension 

femoral head “SPINS” 

-clinically: rolls posterior, glides anterior (sagittal plane)

open chain hip arthrokinematics abduction

rolls superior-lateral and glides inferior-medial (frontal plane)

open chain hip arthrokinematics external rotation

rolls posterior and glides anterior (horizontal plane) 

open chain hip arthrokinematics internal rotation 

rolls anterior and glides posterior (horizontal plane) 

Closed chain Arthrokinematics

pelvis (acetabulum) moving on the fixed femur

Closed Chain sagittal plane motion 

anterior tilt/rotation of the pelvic on the femur (hip joint goes into flexion) 

posterior tilt/rotation of the pelvic on the femur (hip joint goes into extension) 

Closed chain frontal plane: unilateral stance

lateral pelvic tilt (named by what is happening on non weight-bearing side)

weight bearing hip is pivot point for axis of motion

pelvic hike, pelvic drop

pelvic hike

weight bearing hip abducts 

pelvic drop

weight bearing hip adducts

closed chain lateral shift: bilateral stance

pelvic cannot “hike”

both hips will move in frontal plane

if pelvis shifts to the right, right hip joint will be adducted and left hip will be abducted

closed chain transverse plane motion: unilateral stance

forward pelvic rotation:

reference side is side opposite to the rotating hip joint

right forward rotation: left stance leg, right pelvis translates anteriorly

weight bearing hip goes into internal rotation

backward pelvic rotation:

reference side is side opposite to the rotating hip joint

right backward rotation: left stance leg, right pelvis translates posteriorly

weight being hip goes into external rotation

closed chain transverse plane motion: bilateral stance

forward rotation and backward rotation must reference a side

axis of motion occurs around a vertical axis through center of pelvis 

associated lumbar motions

anterior pelvic tilt: hip flexion, lumbar extension

posterior pelvic tilt: hip extension, lumbar flexion

Coupled motion pattersn of the lumbar spine and pelvis

Hip flexion: pelvis on femur (anterior pelvic tilt)

-hip joint flexion

-increases lumbar lordosis

-produced by force-couple between the hip flexors and the erector spinae

hip extension: pelvis on femur (posterior pelvic tilt)

-hip joint extension

-decreases lumbar lordosis

-produced by force-couple between the hip extensors and the rectus abdominis

pelvic rotation during gait

the associated motion in the lumbar spine is in the opposite direction in the transverse plane 

Lumbo-pelvic rhythm

ipsidrectional flexion

-lumbar flexion, anterior pelvic rotation, and hip flexion

-bending forward

-helps maximize motion

contradirectional

-lumbar spine extension

-anterior pelvic rotation

-hip flexion

lumbopelvic rhythm: ipsidirectional

sum of motion of lumbar spine, pelvic, and hip

goal is to maximize motion

controlled by: hip extensors & erector spinae muscles eccentrically

contribution of each segment is dependent on (muscles length, joint mobility, neuromuscular control, and psychosocial factors)

increased shear force across lumbar spine and increase disc pressure compared to contradirectional, decreased hip and knee flexion mobility required

lumbopelvic rhythm from a standing position (forward bending) 

knees extended, forward bending is produced by forward bending of the lumbar spine ~40 degrees 

during initial lumbar flexion the sacrum extends, then begins to flex and the pelvic anterior tilts 

once all pelvic anterior tilt is taken up the hips flex

hips flexion = ~70 degrees

lumbopelvic rhythm: contradirectional

flexion is the sum of the motion of the pelvic and hips

goal: increase stability for lumbar spine and improved lifting mechanics

the lift: lumbar spine goes into extension maintaining the lumbar lordosis and pelvis (ilium and sacrum) anterior tilt and hips flex

decreased shear force across lumbar spine, decreased disc pressure, increased tension on hamstrings and increased knee flexion and hip flexion mobility required

anterior muscle innervation

femoral nerve

medial muscle innervation 

obturator nerve 

lateral muscle innervation

gluteal nerve (superior and inferior) p

posterior muscle innervation

sciatic nerve

-lateral: peroneal portion

-medial: tibial portion

Hip external rotators muscle innervation

ventral Rami S1 and S2 innervate the piriformis

nerve to the obturator internus and superior gemellus 

nerve to the quadratus femoris and inferior gemellus 

quadriceps muscle groups

hamstrings muscle

Anterior peripheral nerve sensory distribution

lateral femoral cutaneous nerve, femoral nerve, obturator nerve, saphenous nerve, common fibular nerve, sural nerve, superficial fibular nerve, deep fibular nerve

posterior peripheral nerve sensory distribution

posterior femoral cutaneous nerve, sural nerve, tibial nerve

primary Hip flexors

iliopsoas, sartorius, tensor fasciae latae, rectus femoris, adductor longus, pectineusse

secondary hip flexors

adductor brevis, gracilis, anterior fibers gluteus minimus

hip flexors 

impact of tight iliopsoas and rectus femoris on hip and lumbar spine

primary hip extensors

gluteus maximus, hamstrings, adductor magnus

hamstring stretch

impact of tight hamstrings on the hip and lumbar spine

primary hip adductors 

pectineus, adductor longus, gracilis, adductor brevis, adductor magnus 

secondary hip adductors

biceps femoris (long head), gluteus maximus (lower fibers), quadratus femoris

Dual action of adductor longus

dual sagittal plane action of the muscle demonstrated during sprinting

hip flexion, muscle is in position to extend the hip, along with the adductor magnus

hip extension, muscle is in position to flex the hip, along with the rectus femoris

actions are based on the change in line of force of the muscle

utilitarian function of the adductors may partially explain their high susceptibility to injury during running and jumping, especially while quickly changing directions

primary hip abductors

gluteus medius, gluteus minimus, tensor fascia latae

secondary hip abductors

piriformis and sartorius

primary hip external rotators

gluteus maximus, piriformis, gemellus superior, gemellus inferior, obturator externus, obturator internus, quadratus femoris

secondary external rotators

obturator externus, posterior fibers of the gluteus medius and minimus, sartorius, long head of the biceps femoris

hip internal rotators 

NO PRIMARY IR because no muscle is oriented in the horizontal plane 

adductors that possibly contribute to hip IR

• adductor longus and brevis

• pectineus

increased hip flexion, hip IR torque increase 

secondary hip internal rotators

anterior fibers of the gluteus medius, gluteus minimus, tensor fasciae latae

pincer and CAM hip impingement

CAM hip impingement

excessive bony growth of the FEMORAL HEAD

leads to poor clearance of the femur specifically with flexion and abduction 

can lead to labral pathology 

pincer hip impingement

excessive bony growth of ACETABULUM

greater coverage of overhang of the acetabulum

causes compression of the superior labrum between rim and head of femur

can lead to labral pathology