Biomech Hip

the ____ is responsible for moving the body to position our upper extremity and hands in space

lower extremity

what segments comprise the lower extremity?

hip/core + knee + ankle/foot

the hip, knee, and ankle/foot are highly coordinated to ...

support the weight of the body (HAT specifically)

the ____ is the link between the upper body and the lower body

hip

what is the primary function of the hip?

support the weight of the head, arms, and trunk in static (standing) and dynamic (gait) postures

T or F: the LE is constantly in an open chain

FALSE; 1/2 the time it is open chain & 1/2 the time it is closed chain

the function of the hip is primarily (mobility/stability)

stability

the hip has ____ DoF. what motions are available at this joint?

3 DoF; flex/ext (S), abd/add (F), IR/ER (T)

list the joints of the hip complex

*coxofemoral*, lumbosacral (L5-S1), sacroiliac, & pubic symphysis

list the bones of the hip complex

femur, innominate (ilium, ischium, pubis), & sacrum

what bones make up the innominate

ilium, ischium, pubis

what is the function of the acetabular labrum?

increases the concavity of the acetabulum which increases stability

T or F: the acetabular labrum does not take loading forces

TRUE; this is good bc it prevents tears

explain the orientation of the acetabulum

anteversion; faces laterally, inferiorly, and anteriorly

(anterior orientation)

what happens to stability of the coxofemoral joint if the acetabular anteversion is increased?

decreased stability (+ increased risk of anterior dislocation)

T or F: due to the acetabular anteversion hyperextension is favored to flexion

FALSE; anterior orientation favors flexion

the femoral neck is angulated to allow the femoral head to face ____, _____, and _____

medially; superiorly; anteriorly

T or F: the acetabulum does not fully cover the femoral head superiorly and anteriorly but it is still considered to be a congruent joint

TRUE

explain the partial vacuum created by the acetabular fossa

- the orientation of the acetabulum creates a suction effect

- maintain joint contact between the femoral head and acetabulum which contributes to stability of the joint

describe the angle of inclination and the normal adult value

the angle between:

- the axis of the femoral head/neck

- the longitudinal axis of the femoral shaft in the frontal plane

normal adults = 125°

T or F: women have a larger angle of inclination

FALSE; men have larger

explain why the angle of inclination is larger in infancy

the angle reduces (to 125) due to the effects of gravity when upright and ambulating

~150° in infancy

_____ describes a pathological angle of inclination that is greater than 125°, meaning that the head and neck point more superiorly

coxa valga

_____ describes a pathological angle of inclination that is less than 125°, meaning that the head and neck point less superiorly

coxa vara

describe the angle of torsion and the normal adult value

the angle between the axis of the femoral head/neck and the axis of the distal femoral condyles in the transverse plane

normal anteversion (normal anterior torsion) = 15-20°

describe the gluteus medius in coxa valga and vara alignments

valga (>125°): glute med length tension (on greater trochanter) is STRETCHED.. decrease torque

vara (

what is the normal angle of torsion?

anteversion (15-20°)

- increases ROM anteriorly (flexion and internal rotation)... needed for functionality

- less ROM posteriorly for hyperextension

_____ describes an angle of torsion beyond 20° and _____ describes an angle of torsion below 15°

excessive anteversion; retroversion

reduced posterior hip ROM is associated with (excessive anteversion/retroversion). why?

excessive anteversion; the femoral head/neck are closer to the posterior acetabulum & the greater trochanter is more posteriorly oriented

reduced anterior hip ROM is associated with (excessive anteversion/retroversion).

retroversion

- decreased flexion

- now closer to a 0° angle of torsion.... theoretical increase in extension

individuals with (excessive anteversion/retroversion) will compensate by turning their toe in

excessive anteversion

explain how the angle of torsion and angle of inclination impact the hip joint when there are abnormalities

CLOSED CHAIN MOVEMENT

compensations at the hip, alter hip stability, and alter weight-bearing biomechanics/ muscle mechanics

T or F: foot or knee injuries might result from hip deviations/pathologies

TRUE; due to closed chain

the articular capsule of the coxofemoral joint is thicker____ and thin/loose ____

anterosuperiorly; posteroinferiorly

list the 3 reinforcing capsular ligaments at the coxofemoral joint

iliofemoral (Y ligament), pubofemoral, ischiofemoral

in what joint position is the ligamentum teres most susceptible to damage?

flexion & adduction (most taut in this position)

***especially bad when leg is in flexion and adduction, yet the proximal trunk still moving (football player injury)

what is the primary function of the ligamentum teres?

transmits secondary blood supply (obturator) to femoral head and provides nerve pathway

damage to the ligamentum teres results in what?

absence of secondary blood supply to femoral head causing increased risk of avascular necrosis

*often leads to need for THA

trabeculae in the proximal femur line up along ____ which form systems to meet stress requirements

stress lines

_____ provides downward forces through the hips and into femoral head and ____ creates upward forces through the femoral shaft.

weight of HAT; ground reaction force (travels up through femoral shaft)

GRF causes (compressive/tensile) forces at the superior femoral neck and HAT causes (compressive/tensile) forces at the inferior femoral neck

tensile; compressive

____ creates bending at the femoral neck

GRF (newton's 3rd law)

explain the 2 major trabecular systems

1. Medial trabecular system: oriented vertically to offset compressive forces from the HAT

2. Lateral trabecular system: oriented obliquely to offset tensile forces from GRF

*medial and lateral accessory systems contribute at the femoral shaft and greater trochanter

The resistance is greatest when the trabecular systems cross each other at _____. Where on the femur does this occur?

right angles; inferior femoral head & inferomedial to greater trochanter

The _____ is the area at which the trabeculae are thin and do not cross and therefore are more susceptible to bending and/or injury. Where on the femur does this occur?

zone of weakness; inferolateral femoral neck

why does regular activity reinforce the trabecular systems?

gravity!

explain how the hip joint works like a Chinese finger puzzle

in flexion the joint capsule/fibers are slack and allow for more translations but in extension the capsule/fibers are taut

T or F: little to no joint distraction occurs at the hip joint

TRUE

how much of our body weight is supported by the hip?

2/3

explain how the concave-convex rule applies to the hip joint during open chain movements

convex moving on concave = OPPOSITE

- convex femoral head glides within the concave acetabulum

- sliding occurs in the OPPOSITE direction of the distal femoral motion (same as shoulder, just less translation)

explain how the concave-convex rule applies to the hip joint during closed chain movements

concave moving on convex = SAME

- hip motion is largely from the pelvis moving on femur

- concave acetabulum articulates with convex femoral head so sliding occurs in the SAME direction as the pelvis motion

_____ is the primary motion of the hip

flex/ext

do we have greater hip flexion ROM with knee ext or flexed

flexed

(extension has greater active/passive insufficiency)

what is the normal ABD/ADD ROM? limits hip ADD? ABD?

ABD (45-50°): limited by gracilis

ADD (20-30°): TFL & ITB limits

what limits hip ext rotation ROM?

excessive anteversion

During flex/ext, what accessory motion(s) occur at the hip joint?

[almost] pure spin of the femoral head around the x-axis

During abd/add, what accessory motion(s) occur at the hip joint?

spinning and gliding of the femoral head (y-axis)

During internal rotation/external rotation, what accessory motion(s) occur at the hip joint?

spinning and gliding of the femoral head (z-axis)

closed chain hip motion occurs largely from the _____ moving on the ____ when all other joints are static.

pelvis; femur

list the normal flexion/extension ROM values at the hip with the knee flexed vs knee extended

knee flexed = 120° flex/

list the normal hip internal rotation/external rotation ROM values

40-50° either direction in 90° knee flexion

(IR/ER) of the hip is measured by moving the foot medially when seated with knees at 90°. (IR/ER) is measured by moving the foot laterally.

ER; IR

what is the close-packed position of the coxofemoral joint?

extension, slight abduction, internal rotation

T or F: optimal articular contact at the coxofemoral joint is in the closed packed position

FALSE;

articular contact is increased in *flexion, abduction, and external rotation* (true physiologic position)

what is the true physiologic position of the coxofemoral joint?

flexion, abduction, external rotation

in what position is the hip at greatest risk for subluxation?

flexion and adduction (occurs when legs are crosses)

***car accident

when knees hit the dashboard during an MVC, the femur dislocates (anteriorly/posteriorly)

posteriorly

describe the position of the ASIS and PSIS in neutral, posterior tilt, and anterior tilt

neutral = ASIS and PSIS are level

posterior = ASIS is superior to PSIS

anterior = ASIS is inferior to PSIS

(anterior/posterior) pelvic tilt is characterized by hip extension and slight external rotation. Describe the lumbar spine in this postion.

posterior; lumbar spine is kyphotic

(anterior/posterior) pelvic tilt is characterized by hip flexion and slight internal rotation. Describe the lumbar spine in this position.

anterior; lumbar spine is severely lordotic

Pelvic tilting causes changes in _____ which rotates the femur

acetabular anteversion

how would you instruct a patient to correct an anterior pelvic tilt? posterior pelvic tilt?

anterior = contract abdominals

posterior = contract glutes

explain lateral pelvic tilt.. where is the AoR

- stance leg in closed chain = AoR

- swing leg in open chain

stance leg becomes the AoR for motion of the contralateral hip as it elevates or drops (frontal plane)

when standing on the L leg, the L hip (abducts/adducts) to hike the R hip

abducts

when standing on the L leg, the L hip (abducts/adducts) to drop the R hip

adducts

when shifting weight to take a step with the R in a bilateral stance, describe the 3 steps to go to unilateral

AoR at left

if we step with R:

1. pelvis must shift to L side to move CoM or HAT and R leg = L ADD

2. R pelvic drop as leg reaches forward and down (AoR at L hip)

3. With R leg now on ground, results in R ABD, L ADD

when shifting weight to the R in a bilateral stance, the (R/L) hip drops. In what plane does this occur?

L hip drops (R becomes stance leg); frontal plane

(L hip rotates around the R hip in frontal plane)

explain forward & backward pelvic rotation

Forward = opposite loaded limb moves anteriorly... IR of supporting (stance) hip

Backward = opposite loaded limb moves posteriorly.. ER of supporting (stance) hip

*occurs in the transverse plane

T or F: the stance leg is the L leg in L pelvic rotation

FALSE; the stance leg is the R leg, the L hip moves forward/backward

L forward rotation: L leg advances forward

L backward rotation: L leg advances backward

What is pelvifemoral rhythm?

coordination of the femur, pelvis, and spine to produce larger ROM at the hip

explain pelvifemoral rhythm in an open chain

- combo of motions increases available ROM at distal segments (foot and head)

- once coxofemoral flexion/abduction is maxed out, the spine will move and reposition the coxofemoral joint (pelvis) to increase ROM

explain pelvifemoral rhythm in a closed chain

- must identify 2 fixed ends (foot and head)

- other joints in the chain, like the spine and pelvis, move to compensate

what activates pelvifemoral rhythm in a closed chain?

structural deviatons: tight hip flexors & leg length discrepancies

dynamic problems: pelvic drop & hip hike

explain the open chain compensation to tight hip flexors

hip flexors pull on pelvis and HAT will move forward in response

explain the closed chain compensation to tight hip flexors

- anterior pelvic tilt will occur

- leading to increased lumbar lordosis and thoracic kyphosis to keep the head over the hips

explain inversion of function

the joint position influences the function of a given muscle

_____ is the most important hip flexor

iliopsoas

what is the open chain function of the hip flexors?

- primary function: MOBILITY (flex the hip to swing leg)

- secondary function: resist hip extension forces

what is the closed chain function of the hip flexors?

increase lumbar lordosis as trunk & head extend to compensate

T or F: iliopsoas flexes the trunk when in neutral upright position

FALSE; iliopsoas is active when moving from trunk extension to neutral

does iliopsoas m. assist in hip flexion from a seated position?

no - hip is already flexed (lean too far forward, hip flexion is due to gravity)

____ is responsible for hip flexion, abduction, and external rotation but is most functional when simultaneous hip and knee flexion occur

sartorius

_____ flexes the hip but it's force generating capacity is affected by the position of the knee since it is also a knee extensor

rectus femoris

during simultaneous knee extension and hip flexion, rectus femoris is susceptible to _____

active insufficiency

what position is the rectus femoris the best contributor to hip flexion

when the knee is flexed

Action of TFL

- flexes, abducts, and internally rotates the hip

- mostly responsible for maintaining tension in the ITB

_____ is a strong hip extensor with a long moment arm

gluteus maximus

**longer moment arm than hamstrings and adductor magnus

_____ are a group of muscles that act to extend the hip and flex the knee

hamstrings

when the hip is flexed and the knee is extended the hamstrings are susceptible to _____

passive insufficiency

when the hip is extended and the knees is flexed beyond 90°, the hamstrings are susceptible to ______

active insufficiency