Slips & Falls: Biomechanics & Usability

1. Slips & Falls: Biomechanics & Usability AdityaJayadas, PhD Assistant Professor Dept. of Design, Housing & Merchandising Oklahoma State University OSU Medical School, Tulsa Dec 5th, 2014

2. Quote “Human walking is a unique activity during which the body, step by step, teeters on the brink of catastrophe …. only the rhythmic forward movement of first one leg and then the other keeps man from falling flat on his face” - Napier, J. R. (1967)

3. Falls: A growing problem in the elderly? Incidence 1 in 3 - Hausdorff et al., 2001 15,800 elderly fatal fall-related injuries in 2005 - CDC, 2008 Gender differences Men – 49% higher chance of dying from a fall - CDC, 2005 Women twice as likely to have a non-fatal injury - Stevens et al., 2005 Slip & Fall 66% of all fall-related fractures  Slippery surfaces - Norton et al. (1997) Cost U.S. $0.2 billion  fatal + U.S. $19.2  non-fatal (in 2000) - Stevens How many older individuals in the US by 2030?

4. So, falls are a serious problem …And it could get worse Close to 35 million individuals >65yrs residing in the U.S. in 2000 Expected: Close to 71.5 million (20% of the population) in 2030 - U.S Census Bureau, 2006

5. So, falls are a serious problem …What are the causes of falls? Fatalities Non-fatal Injuries No Injuries Causes of Falls Intrinsic Factors Extrinsic Factors Falls

6. Falls: Two factors Extrinsic Environmental Obstacles in path, worn-out shoes, contaminants on the floor, poor lighting, absence of rails … Intrinsic Changes associated with aging Poor vision, cognition impairment, reduced lower extremity strength, poor balance … Medication Makes individuals more prone to falls Nutrition Calcium and Vitamin D deficiency Lack of exercise/physical activity Poor balance, fear of falling - adapted from Masud & Morris (2001)

7. What about causes as they relate to types of falls? Two major types - Goetsch, D. L., 2005 Falls from an elevation 10% of fall-related fatalities  Stair-related 75% during descent - as cited in Masud & Morris (2001) Falls on the same level Step/stomp and fall Trip and fall 12-22% of all fall-related hip fractures in elderly - as cited in Pavol et al. (2001) Slip and fall 66% of all fall-related fractures occurred on slippery surfaces - Norton et al. (1997)

8. Trips & falls Three primary mechanisms Elevating falls (Contra-lateral) Faster walking velocity Increased lumbar flexion Lowering falls (Ipsi-lateral) During-step falls Faster walking velocity After-step falls More anterior HAT-COM Increased lumbar flexion Buckling of recovery limb - Pavol et al., 2001

9. Trips & falls: If you have higher strength will you fall less often? Hip - Knee - Ankle High strength During-step /Elevation fall Fast walking velocity Low strength After-step fall Slow response - Pavol et al., 2002 - Biodex Fall Risk Assesment Program, 2003

10. Biomechanics of Slips & Falls LOW COF Floor surface - Redfern & Bidanda, 1994 Type of footwear - Menz et al., 2001 Higher heel contact velocity Elderly > Young - Lockhart et al., 2003 Unable to bring COM over perturbed foot  Fall - You et al., 2001 Increased A-P COM vel.  Recovery - Lockhart et al. 2003 Do individuals walk differently to begin with? Age, floor condition & Arm restriction??

11. Biomechanics of Slips & Falls Rapid arm movement crucial for recovery - Marigold et al., 2003 Helps move HAT COM Backward boundary of BOS Arm response Reduced trunk vel. following slip Reposition trunk - Troy et al., 2009 Age Young More effective in reducing trunk extension vel. Rapid flexion of shoulders - Troy et al., 2009

12. A slip & fall event Adapted from Gronqvist et al., 2001

13. Subjects 28 Screening Ability to participate No health problems IRB Approval Self-assessment Practice

14. Methods Gait trials 8-camera 120hz Butterworth Filter Cut-off frequency - 6hz Dry walking & Proactive 3*3*2 & 2*3*2 Mixed factor model Reactive Diff in Age Diff b/w fallers & non-fallers Role of arm restriction Significance level 0.05

15. Fall Frequency Elderly - 8 individuals fell Young - 3 individuals fell

16. Observation of successful strategies

17. Right shoulder extension- abduction Cross-over step Left shoulder extension- abduction Both shoulders extension- abduction

18. Sliding strategy Braking strategy

19. Tucking in of left arm Safe placement of non-sliding leg Trunk twisting- leaning Leg spring up

21. Observation of unsuccessful reactive movements

22. Momentum- forward fall Leg collapse Too much lean to the left Less effective braking

23. Unable to get non-sliding leg to the floor Poor placement of initial non-sliding leg Less effective trunk strategy Less effective use of arms

24. Let’s look at a few Variables Dry walking & Proactive Heel Contact Vel., Foot Floor Angle, Norm. Step Length & Walking Vel. Reactive Slip distance WBCOM calculation (Lockhart, 2000) LBCOM Left & Right Thighs, Legs & Feet 6 segments UBCOM Head & Neck, Trunk, Right & Left Upper Arms & Forearms with hands 6 segments WBCOM, UBCOM, LBCOM & Heel slipping vel. Finite differences

25. Results FALL 14/84 trials resulted in fall 9 Trials involved elderly individuals Proactive strategies & Arm Restriction  Age Validation of previous literature Max. Vel. Diff. b/w WBCOM & sliding heel Trailing and leading  Both not significant Max. Vel. Diff. b/w LBCOM & UBCOM Trailing and leading  Both significant

26. Results

27. Results Age & Arm Restriction No Sig. diff. Fallers & Non-fallers P<0.001

28. Results Fallers & Non-fallers P = 0.04

29. Results When WBCOM is trailing the heel Diff. b/w fallers & non-fallers P=0.24 When WBCOM is leading the heel Diff. b/w fallers & non-fallers P= 0.47

30. Results When LBCOM is trailing the UBCOM Diff. b/w fallers & non-fallers P=0.003* When LBCOM is leading the UBCOM Diff. b/w fallers & non-fallers P= 0.02*

31. Results Taking age into account Fallers  Old vs Young  P = 0.03* Non-Fallers  Old vs Young  P = 0.003*

32. Discussion Increased vel. diff. b/w LBCOM & UBCOM Older fallers Young non-fallers Young individuals who arrested trunk extension angular vel. recovered -Grabiner et al., 2008 UBCOM vel.  Trunk + Arm motion Trunk (Troy et al., 2008) Rapid arm movement (Marigold et al. 2003) LBCOM Not reported Slipping.. leading & trailing leg (Margerum 2005) WBCOM & Heel diff. in vel. did not show diff. b/w fallers & non-fallers Decreased vel. slipping foot relative to COM (Troy et al. 2008)

33. Discussion Proposed method WBCOM – Heel approach Lower body WBCOM calculation Trunk movement crucial to recovery with the aid of arms  UBCOM LBCOM  leading-trailing leg dynamics Fallers & non-fallers No force plate is needed Limitation Circular track  Limited speed Possible anticipation Future Direction Explore LBCOM-UBCOM dynamics further Validate Individuals who practice Tai-Chi better? Arm restriction Nature of the load

34. No-, 2- & 1- arm restrictionwalking trials?? 2- arm 1- arm No- arm

37. What about strength? Fallers vs Non-fallers  No sig. diff. Rate of torque development  No sig. diff.

38. Fallers .. Impact Vel. 6 backward fall trials 3.22 ± 0.5m/s >2m/s risk Okiuzumi et al. (1998) 2000-4000N Head of femur breaks in elderly Robinovitch et al. (1995) ↓ BMI ↑ Hip fracture Wu & Xue (2008) Pre-impact fall detector Airbag Falls do occur prior to impact What can we do?

39. Hip Protection Pads • Usability? • Elderly • Engineers make assumptions • Questionnaires & Interviews

40. What I would like to do… Biomechanics EMG, EEG, Strength Walking & Slips Design Hip protection pads Clothing& Footwear Ergonomics Usability Hip Protection pads Footwear Eng. & Admin. Controls Personal Protective Equipment

41. Take Away LBCOM-UBCOM dynamics Successful “catch up”key to recovery What can I tell my neighbor who is 81yrs young? Coordinated upper & lower body motions  Tai chi Strengthen core also Improve shoulder mobility Stay active Capabilities & limitations Improve reaction time Hip protection pad

42. Questions to Ponder Kinect? Glasses? Elderly & heels?

43. Questions I am taking your advice, Dr. Slip Jayadas, & letting go of the soda & popcorn … aditya.jayadas@okstate.edu

44. Thank you!!