Slips & Falls: Slips & Falls: Biomechanics & UsabilityBiomechanics & Usability

Aditya Jayadas, PhDAditya Jayadas, PhDAssistant ProfessorAssistant Professor

Dept. of Design, Housing & MerchandisingDept. of Design, Housing & Merchandising

Oklahoma State UniversityOklahoma State University

OSU Medical School, TulsaOSU Medical School, Tulsa

Dec 5Dec 5thth, 2014, 2014

QuoteQuote

““Human walking is a unique activity during which Human walking is a unique activity during which the body, step by step, teeters on the brink of the body, step by step, teeters on the brink of

catastrophe …. only the rhythmic forward catastrophe …. only the rhythmic forward movement of first one leg and then the other movement of first one leg and then the other keeps man from falling flat on his facekeeps man from falling flat on his face””

- - Napier, J. R. (1967)Napier, J. R. (1967)

Falls: A growing problem in the Falls: A growing problem in the elderly? elderly?

IncidenceIncidence 1 in 31 in 3

- - Hausdorff et al., 2001Hausdorff et al., 2001

15,800 elderly fatal fall-related injuries in 200515,800 elderly fatal fall-related injuries in 2005- CDC, 2008- CDC, 2008

Gender differencesGender differences• Men – 49% higher chance of dying from a fall Men – 49% higher chance of dying from a fall

- CDC, 2005- CDC, 2005

• Women twice as likely to have a non-fatal injuryWomen twice as likely to have a non-fatal injury- Stevens et al., 2005- Stevens et al., 2005

Slip & FallSlip & Fall 66% of all fall-related fractures 66% of all fall-related fractures Slippery surfaces Slippery surfaces

- Norton et al. (1997)- Norton et al. (1997)

CostCost U.S. $0.2 billion U.S. $0.2 billion fatal + U.S. $19.2 fatal + U.S. $19.2 non-fatal (in 2000) non-fatal (in 2000)

- Stevens- Stevens How many older individuals in the US by 2030?How many older individuals in the US by 2030?

So, falls are a serious problem …So, falls are a serious problem …And it could get worseAnd it could get worse

Close to 35 million individuals >65yrs residing in the U.S. in 2000Expected: Close to 71.5 million (20% of the population) in 2030

- U.S Census Bureau, 2006

So, falls are a serious problem …So, falls are a serious problem …What are the causes of falls?What are the causes of falls?

Extrinsic Factors Intrinsic Factors

Fatalities Non-fatal Injuries No Injuries

Causes of Falls

Falls

Falls: Two factorsFalls: Two factors

Extrinsic Extrinsic EnvironmentalEnvironmental

• Obstacles in path, worn-out shoes, contaminants on Obstacles in path, worn-out shoes, contaminants on the floor, poor lighting, absence of rails …the floor, poor lighting, absence of rails …

Intrinsic Intrinsic Changes associated with agingChanges associated with aging

• Poor vision, cognition impairment, reduced lower Poor vision, cognition impairment, reduced lower extremity strength, poor balance …extremity strength, poor balance …

MedicationMedication• Makes individuals more prone to fallsMakes individuals more prone to falls

NutritionNutrition• Calcium and Vitamin D deficiencyCalcium and Vitamin D deficiency

Lack of exercise/physical activityLack of exercise/physical activity• Poor balance, fear of fallingPoor balance, fear of falling

- adapted from Masud - adapted from Masud & Morris (2001)& Morris (2001)

What about causes as they relate What about causes as they relate to types of falls?to types of falls?

Two major types Two major types - Goetsch, D. L., 2005- Goetsch, D. L., 2005

Falls from an elevationFalls from an elevation• 10% of fall-related fatalities 10% of fall-related fatalities Stair-related Stair-related

75% during descent75% during descent- as cited in Masud - as cited in Masud

& Morris (2001)& Morris (2001) Falls on the same levelFalls on the same level

• Step/stomp and fallStep/stomp and fall• Trip and fallTrip and fall

12-22% of all fall-related hip fractures in elderly 12-22% of all fall-related hip fractures in elderly - as - as cited in Pavol et al. (2001)cited in Pavol et al. (2001)

• Slip and fallSlip and fall 66% of all fall-related fractures occurred on slippery surfaces66% of all fall-related fractures occurred on slippery surfaces

- Norton et al. - Norton et al. (1997)(1997)

Trips & fallsTrips & falls

Three primary mechanisms Three primary mechanisms Elevating falls (Contra-lateral)Elevating falls (Contra-lateral)

• Faster walking velocity Faster walking velocity • Increased lumbar flexionIncreased lumbar flexion

Lowering falls (Ipsi-lateral)Lowering falls (Ipsi-lateral)• During-step fallsDuring-step falls

Faster walking velocityFaster walking velocity

• After-step fallsAfter-step falls More anterior HAT-COM More anterior HAT-COM Increased lumbar flexion Increased lumbar flexion Buckling of recovery limbBuckling of recovery limb

- Pavol et al., - Pavol et al., 20012001

Trips & falls: If you have higher Trips & falls: If you have higher strength will you fall less often?strength will you fall less often?

Hip - Knee - AnkleHip - Knee - Ankle High strengthHigh strength

• During-step /Elevation fallDuring-step /Elevation fall Fast walking velocityFast walking velocity

Low strengthLow strength• After-step fallAfter-step fall

Slow responseSlow response

- Pavol et - Pavol et al., 2002al., 2002

- Biodex Fall Risk Assesment Program, 2003

Biomechanics of Slips & Biomechanics of Slips & FallsFalls

LOW COFLOW COF Floor surfaceFloor surface

- Redfern & - Redfern & Bidanda, 1994Bidanda, 1994

Type of footwearType of footwear- Menz et al., 2001- Menz et al., 2001

Higher heel contact velocity Higher heel contact velocity Elderly > YoungElderly > Young

- Lockhart et al., - Lockhart et al., 20032003

Unable to bring COM over perturbed foot Unable to bring COM over perturbed foot Fall Fall- You et al., 2001- You et al., 2001

Increased A-P COM vel. Increased A-P COM vel. Recovery Recovery- Lockhart et al. 2003- Lockhart et al. 2003

Do individuals walk differently to begin with? Age, floor condition & Arm restriction??

Biomechanics of Slips & FallsBiomechanics of Slips & Falls

Rapid arm movement crucial for recoveryRapid arm movement crucial for recovery- Marigold et al., 2003- Marigold et al., 2003

Helps move HAT COMHelps move HAT COM• Backward boundary of BOSBackward boundary of BOS

Arm response Arm response Reduced trunk vel. following slip Reduced trunk vel. following slip Reposition trunkReposition trunk

- Troy et al., 2009- Troy et al., 2009 AgeAge

YoungYoung• More effective in reducing trunk extension vel. More effective in reducing trunk extension vel. • Rapid flexion of shouldersRapid flexion of shoulders

-- Troy et al., 2009 Troy et al., 2009

A slip & fall eventA slip & fall event

Adapted from Gronqvist et al., 2001

SubjectsSubjects 2828

ScreeningScreening• Ability to participateAbility to participate

No health problemsNo health problems IRB ApprovalIRB Approval Self-assessmentSelf-assessment

• PracticePractice

MethodsMethods Gait trialsGait trials

8-camera8-camera• 120hz120hz

Butterworth Filter Butterworth Filter • Cut-off frequency - 6hzCut-off frequency - 6hz

Dry walking & ProactiveDry walking & Proactive 3*3*2 & 2*3*2 Mixed factor model3*3*2 & 2*3*2 Mixed factor model

ReactiveReactive Diff in AgeDiff in Age Diff b/w fallers & non-fallersDiff b/w fallers & non-fallers Role of arm restrictionRole of arm restriction

Significance level Significance level 0.050.05

Fall FrequencyFall Frequency

Elderly - 8 individuals fellYoung - 3 individuals fell

Observation of successful strategiesObservation of successful strategies

Arm Restriction

S.No. Successful strategy No Arm Two Arm 1 Arm Total

1 Right shoulder extension-abduction 3 0 3 6

2 Left shoulder extension-abduction 1 1 5 7

3 Both shoulders extension-abduction 14 7 9 30

4 Left arm tuck in 0 0 2 2

5 Sliding strategy 1 1 3 5

6 Braking strategy 9 8 5 22

7 Safe placement of non-sliding leg 8 9 11 28

8 Cross-over step 2 3 4 9

9 Trunk twist-lean 5 13 11 29

10 Leg spring up 0 4 1 5

143

Cross-overstep

Both shouldersextension-abduction

Right shoulderextension-abduction

Left shoulderextension-abduction

Braking strategy

Sliding strategy

Tuckingin of

left arm

Legspring

up

Safeplacement

of non-slidingleg

Trunktwisting-leaning

Observation of unsuccessful reactive Observation of unsuccessful reactive movementsmovements

Arm Restriction

S.No. Unsuccessful reactive movements No Arm Two Arm 1 Arm Total

1 Leg collapse 3 2 1 6

2 Momentum - forward fall 2 1 0 3

3 Less effective braking strategy 3 1 0 4

4 Too much lean to the left 5 2 2 9

5 Poor placement of initial non-sliding leg 4 1 1 6

6 Unable to get non-sliding leg to the floor 3 0 0 3

7 Less effective trunk strategy 1 1 0 2

8 Less effective arm strategy 1 3 1 5

39

Legcollapse

Lesseffective braking

Momentum-forward

fall

Too muchlean tothe left

Unable toget

non-slidingleg to the

floor

Lesseffective

use ofarms

Poorplacement of initial

non-slidingleg

Less effective

trunkstrategy

LetLet’’s look at a few s look at a few VariablesVariables

Dry walking & ProactiveDry walking & Proactive Heel Contact Vel., Foot Floor Angle, Norm. Step Length & Heel Contact Vel., Foot Floor Angle, Norm. Step Length &

Walking Vel.Walking Vel.

ReactiveReactive Slip distanceSlip distance WBCOM calculation WBCOM calculation (Lockhart, 2000)(Lockhart, 2000)

LBCOMLBCOM• Left & Right Thighs, Legs & Feet Left & Right Thighs, Legs & Feet

6 segments6 segments

UBCOMUBCOM• Head & Neck, Trunk, Right & Left Upper Arms & Forearms with hands Head & Neck, Trunk, Right & Left Upper Arms & Forearms with hands

6 segments6 segments

WBCOM, UBCOM, LBCOM & Heel slipping vel.WBCOM, UBCOM, LBCOM & Heel slipping vel.• Finite differencesFinite differences

ResultsResults FALLFALL

14/84 trials resulted in fall14/84 trials resulted in fall 9 Trials involved elderly individuals9 Trials involved elderly individuals

Proactive strategies & Arm Restriction Proactive strategies & Arm Restriction Age Age Validation of previous literatureValidation of previous literature

Max. Vel. Diff. b/w WBCOM & sliding heelMax. Vel. Diff. b/w WBCOM & sliding heel Trailing and leading Trailing and leading Both not significant Both not significant

Max. Vel. Diff. b/w LBCOM & UBCOMMax. Vel. Diff. b/w LBCOM & UBCOM Trailing and leading Trailing and leading Both significant Both significant

ResultsResults

ResultsResults

Age & Arm RestrictionNo Sig. diff.

Fallers & Non-fallersP<0.001

Fallers & Non-fallersP = 0.04

ResultsResults

ResultsResults

When WBCOM is leading the heelDiff. b/w fallers & non-fallers

P= 0.47

When WBCOM is trailing the heelDiff. b/w fallers & non-fallers

P=0.24

ResultsResults

When LBCOM is leading the UBCOMDiff. b/w fallers & non-fallers

P= 0.02*

When LBCOM is trailing the UBCOMDiff. b/w fallers & non-fallers

P=0.003*

ResultsResults

Taking age into accountFallers Old vs Young P = 0.03*Non-Fallers Old vs Young P = 0.003*

DiscussionDiscussion Increased vel. diff. b/w LBCOM & UBCOMIncreased vel. diff. b/w LBCOM & UBCOM

Older fallers Older fallers Young non-fallersYoung non-fallers

• Young individuals who arrested trunk extension angular vel. recovered Young individuals who arrested trunk extension angular vel. recovered

-Grabiner et -Grabiner et al., 2008al., 2008

UBCOM vel. UBCOM vel. Trunk + Arm motion Trunk + Arm motion Trunk (Troy et al., 2008)Trunk (Troy et al., 2008) Rapid arm movement (Marigold et al. 2003)Rapid arm movement (Marigold et al. 2003)

LBCOMLBCOM Not reportedNot reported Slipping.. leading & trailing leg (Margerum 2005)Slipping.. leading & trailing leg (Margerum 2005)

WBCOM & Heel diff. in vel. did not show diff. b/w WBCOM & Heel diff. in vel. did not show diff. b/w fallers & non-fallersfallers & non-fallers

Decreased vel. slipping foot relative to COM (Troy et al. 2008)Decreased vel. slipping foot relative to COM (Troy et al. 2008)

DiscussionDiscussion Proposed methodProposed method

WBCOM – Heel approachWBCOM – Heel approach• Lower body Lower body WBCOM calculationWBCOM calculation

Trunk movement crucial to recovery with the aid of arms Trunk movement crucial to recovery with the aid of arms UBCOM UBCOM

LBCOM LBCOM leading-trailing leg dynamics leading-trailing leg dynamics Fallers & non-fallersFallers & non-fallers No force plate is neededNo force plate is needed

LimitationLimitation Circular track Circular track Limited speed Limited speed Possible anticipationPossible anticipation

Future DirectionFuture Direction Explore LBCOM-UBCOM dynamics furtherExplore LBCOM-UBCOM dynamics further

• ValidateValidate• Individuals who practice Tai-Chi better?Individuals who practice Tai-Chi better?• Arm restrictionArm restriction

Nature of the loadNature of the load

No-, 2- & 1- arm restrictionNo-, 2- & 1- arm restrictionwalking trials??walking trials??

No- arm

2- arm1- arm

What about strength?What about strength?

Fallers vs Non-fallers No sig. diff.Rate of torque development No sig. diff.

Fallers .. Impact Vel.Fallers .. Impact Vel. 6 backward fall trials6 backward fall trials

3.22 ± 0.5m/s3.22 ± 0.5m/s >2m/s risk >2m/s risk

Okiuzumi et al. (1998)Okiuzumi et al. (1998) 2000-4000N 2000-4000N

• Head of femur breaks in elderlyHead of femur breaks in elderly

Robinovitch et al. (1995)Robinovitch et al. (1995) ↓ ↓ BMI ↑ Hip fractureBMI ↑ Hip fracture

Wu & Xue (2008)Wu & Xue (2008) Pre-impact fall detectorPre-impact fall detector

• Airbag Airbag

Falls do occur prior to impactFalls do occur prior to impact

What can we do?

Hip Protection PadsHip Protection Pads

Usability?•Elderly•Engineers make assumptions•Questionnaires & Interviews

What I would like to do…What I would like to do…

Biomechanics EMG, EEG, Strength

Walking & Slips

UsabilityHip Protection pads

Footwear

Design Hip protection padsClothing& Footwear

Ergonomics

Eng. & Admin. ControlsPersonal Protective Equipment

Take AwayTake Away LBCOM-UBCOM dynamicsLBCOM-UBCOM dynamics

Successful Successful ““catch upcatch up”” keykey to recovery to recovery

What can I tell my neighbor who is 81yrs young?What can I tell my neighbor who is 81yrs young? Coordinated upper & lower body motions Coordinated upper & lower body motions Tai chi Tai chi Strengthen core alsoStrengthen core also Improve shoulder mobilityImprove shoulder mobility Stay active Stay active

• Capabilities & limitationsCapabilities & limitations Improve reaction timeImprove reaction time Hip protection padHip protection pad

Questions to Ponder

Elderly & heels? Glasses?

Kinect?

QuestionsQuestions

aditya.jayadas@okstate.edu

I am taking your advice, Dr. Slip Jayadas, & letting go of the soda & popcorn …

Thank you!!