Knee-Thigh-Hip Injuries and Knee/Femur Compliance of the Hybrid

III, Thor-Lx, and Human Cadavers

Shashi Kuppa, NHTSAJonathan Rupp, UMTRILarry Schneider, UMTRI

2

KTH Injury Scenario in Frontal CrashesKTH Injury Scenario in Frontal Crashes

Body motion

Bolster-to-knee impact force

Force applied at the knee is transmitted through the

thigh and to the hip

3

Michigan CIREN Center

Mechanisms of injury Hip injuries in Frontal CrashesMechanisms of injury

4

Risk of AIS 2+ Injury in Different Restraint Environments (NASS/CDS 1993-2001)

0%2%4%6%8%

10%12%14%

head

neck

thorax/ab

duppere

xlowere

x

KTHbelo

w knee

Ris

k of

AIS

2+

Inju

ries

bag+belt bag only belt only unrestr

5

Annual LLI per 100 Front Seat Occupants in different Restraint Environments (NASS/CDS 1993-2001)

0123456789

10

head/fa

ce

neck

thorax/ab

duppere

xlowere

x

KTHbelo

w knee

LLI (

year

s) p

er 1

00 O

ccup

ants

belt+bag bag belt only unrestr

6

Risk of KTH injuries of restrained occupants by air bag presence (NASS/CDS 1993-2001)

0.0%

0.1%

0.2%

0.3%

0.4%

0.5%

Airbag No Airbag

Ris

k of

AIS

2+

Inju

ry hip thigh knee

3-point belt restrained occupants

7

Risk of KTH Injuries in air bag equipped vehicles by vehicle model year (NASS/CDS 1993-2001)

0.0%

0.2%

0.4%

0.6%

0.8%

pre93 93-96 97-01Vehicle Model Year

Ris

k of

Inju

ry

hip thigh knee

3-point belt restrained occupants

8

FMVSS 208 and NCAP Test Data

02000400060008000

1000012000

87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02

Fem

ur F

orce

(N)

Model Year

FMVSS 208 (unrestrained HIII dummy in 48 km/h frontal crash)

0

20004000

6000

8000

1000012000

14000

86 87 88 89 90 91 92 93 94 95 96 97 98 99 00 01 02 03

Fem

ur F

orce

(N)

Model Year

NCAP (restrained HIII dummy in 56 km/h frontal crash

9

Forc

e (k

N)

Time (ms)

0

5

10

15

20

25

0 10 20 30 40 50

Melvin 1980. SledPadded knee stop

Leung 1983. SledPadded knee stop

Powell, 1975. Rigidimpactor

Cheng, 1984. Sled1983 VW Rabbit bolster

Melvin 1976. Lightlypadded impactor

X

X

XX

X KTH fracture

FMVSS 208 compliance testresults from a 2000 Taurus

X

Loading Rates in Previous Studies

Inertial Effects on Loading of the KTH Complex

Force

Forc

e

Distance along femur

Forc

e

t

knee

femur

hip

11

0

4

8

12

16

20

0 10 20 30 40 50 60

Effect of Joint Compliances on Short- and Long-Duration Loads

Force at knee

Force at hip

Forc

e (k

N)

Time (ms)Lag from compliance of knee and hip

X

High loading rate(Melvin et al. 1976)

Low loading rate

FMVSS 208

Hip tolerance

12

UMTRI Hip Tolerance TestingSchematic of test fixture

Weightedplatform Hexcel

Molded knee

interface

RamImpactsurface

Reaction force load cell (rigidly

mounted)

Pneumaticaccelerator

Applied force load cell

13

Time (ms)

Forc

e (k

N)

Rate of Loading in UMTRI Knee Impact Tests

300 N/ms

Typical loading rates in FMVSS 208 tests are also less than 300 N/ms while the loading ratesin previous research were 400-3000 N/ms.

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Femur Tolerance Testing

Reaction force load

cell

Force

• Same apparatus as hip tolerance tests.

• Same specimens as those used in the hip tolerance tests with hip disarticulated and the head of femur inserted in an acetabular cupfixed to the support.

Femur Tolerance Testing

0

0.2

0.4

0.6

0.8

1

Hip

Tol

eran

ce a

s a

%ag

e of

Fe

mur

Tol

eran

ce

Test

Femur tolerance

Relative hip

tolerance

The femur is stronger than the acetabulum (P<0.01)Hip tolerance is 72±7% of femur tolerance

16

Results of impact tests• Neutral posture hip fracture tolerance is 5.7±1.4 kN• Femur fracture tolerance is 7.6 ± 1.6 kN• Femoral neck is the weakest part of the femur.• Using the displacement of the ram and the force

applied at the knee, • The stiffness of knee-thigh-hip complex is 233 N/mm• The stiffness of knee-femur complex is 370 ± 80 N/mm

17

Stiffness of Human Cadaver Knee/Femur complex at loading rates seen in 30 mph frontal crashes (FMVSS208)

0

5000

10000

15000

20000

0 22Deflection (mm)

Forc

e (N

)

Up bound= 500 N/mm

low bound= 260 N/mm

Most of the knee-femur axial compliance is due to femur bending rather than the compliance at the knee joint.

18

Hybrid III Knee-thigh-hip Complex• Hybrid III knee-thigh stiffness based on fixed femur skeletal

response of knee+distal femur sections by Horsch and Patrick (1976).

• Compliance of knee padding was selected such that HIII knee+distal femur response matches the Horsch-Patrick data

• Donnelly and Roberts (1987) found the Hybrid III to produce three times greater force than cadaveric subjects in whole-body knee impact tests.

19

Thor Knee-thigh-hip Complex• To better match Donnelly and Roberts data, Thor has a

compliant element in the mid femur and redistributes some of the thigh mass to the flesh.

• The knee design is similar to the Hybrid III knee with similar impact response characteristics. It has rigid hemispherical knee caps intended to provide more human-like interaction with the knee bolster.

20

Knee-femur compliance of Hybrid III, Thor and cadaver in molded knee interface loading at rates similar to that seen in 30 mph frontal crashes

0

5000

10000

15000

20000

0 5 10 15Deflection (mm)

Froc

e (N

)

Hybrid III (8100 N/mm)Thor (1400 N/mm)

Cadaver up bound (500 N/mm)

Initial stiffness (1800 N/mm) of HIII knee-femur is due to compression of knee padding. After about 2 mm, the HIII stiffness increases to 8100 N/mm, which reflects the rigidity of the femurand the limited compliance offered by knee padding.

21

Compliance of ATDs at typical loading rates seen in FMVSS 208 frontal crashes

Thor Knee/Femur Compliance = 3 X Cadaver Knee/Femur compliance

Hybrid III Knee/Femur Compliance = 16 X Cadaver Knee/Femur Compliance

The Thor has a less stiff force deflection response than the Hybrid III dummy due to the compliant element in the Thor femur

22

Biofidelity of ATDs• Biofidelity of an ATD’s knee-thigh complex depends

on knee/femur stiffness, as well as inertial contributions of the knee/femur complex and other body regions.

• In order to address mass-coupling issues, knee impacts to whole body cadavers and ATDs (free back condition) will be conducted.

• Though the Thor knee-femur stiffness is 3 times greater than that of human cadavers, its response under dynamic knee loading, such as in frontal crashes, may be similar to that of human cadavers.

23

New Knee Bolster Designs

With the advent of new knee bolster designs, such as inflatablebolsters, the biofidelity of the knee-thigh-hip complex of the ATDand appropriate injury criteria will become crucial to ensure adequate protection for the KTH complex in frontal crashes.