SLIPS, TRIPS, & FALLS (STF) Charles N. Brooks, MD

Transcription

1 SLIPS, TRIPS, & FALLS (STF) Charles N. Brooks, MD

2 Financial Disclosure Charles N. Brooks, MD has no financial relationship with any commercial entity regarding any of the topics to be presented.

3 ACKNOWLEDGEMENT Some slides borrowed or paraphrased from: Accident reconstructionist Rob Stearns Biomechanists Rick Robertson Jim Funk

4 SLIPS, TRIPS, & FALLS High potential for injury and death. However, also a frequent source of fraudulent claims.

5 OUTLINE Magnitude of problem of STF Review Basic Physics (Mechanics) Gait Cycle Types of Falls Slips Common causes of slips and trips Prevention Causation Analysis Investigation Case studies

6 MAGNITUDE OF THE PROBLEM OF STF

7 Costly Problem in Morbidity, Mortality, and Monetarily #1 cause of need for treatment after trauma 2 nd leading cause of accidental death in US (over 17,000 per year), behind only motor vehicle collisions, and most frequent cause in the elderly Most frequent type of premises liability

8 Are STF a Big Problem at Work? About ¼ (15-40%) disabling work injuries Annual direct cost in US for falls at work is over $6 billion Average direct cost for a disabling fall over $28,000, indirect over $46,000 Over 5000 workers die/year from falls

9 REVIEW OF BASIC PHYSICS (MECHANICS)

10 Physics Most injuries involve force application to the body that causes a change in motion Hence to adequately assess STF must know some basic mechanics.

11 Velocity Velocity = change in displacement per unit time (v = d/ t) Change in velocity = v

12 Acceleration Acceleration = change in velocity per unit time (a= v/ t) Acceleration due to gravity = g Deceleration = negative acceleration

13 Force Force = mass X acceleration (F=ma) Force tends to change a body s state of rest or motion

14 It s not the fall but the sudden stop at the end Injury producing potential is not so much the velocity change, but how fast it occurs (deceleration). Faster the v, higher the likelihood of injury.

15 Example- 2 Falls from Same Height, Different Impact Force Fall headfirst 30 feet Diving off 10 m platform into a pool slow deceleration low F no injury onto concrete rapid deceleration high F usually dead It's not the fall that kills you, but the sudden stop

16 Coefficient of Friction (COF) Unitless number indicating slip resistance of a surface (traction) Calculated by dividing force it takes to slide an object across surface by its weight

17 Center of Gravity or Mass (COG) Balance point of a a body If rotation, it's the axis COG in humans in midline of pelvis about 55% of person's height, anterior to S2 Location affects if and how falls occur

18 GAIT CYCLE

19 Gait Cycle

20 Terms Stride length Distance between 2 successive heel strikes of the same foot (distance traveled in 1 complete gait cycle) Step length Distance between 2 successive heel strikes of opposite feet

21 Gait Variations Gait varies with: Injury or disease Body weight Age Speed Environment

22 TYPES OF FALLS

23 Types of Falls From height (elevated fall) More severe but less frequent Most (60%) 10' From same level (or surface) More frequent but less severe

24 Same Level Falls - 4 Types 1. Slip and fall (SAF) 2. Trip and fall (TAF) 3. Step and fall 4. Stump and fall

25 Slip and Fall (SAF) Most common same level fall Cause: insufficient friction between shoe & floor Example: slip on wet or greasy kitchen floor

26 Slippery Fall One can walk on very slippery surfaces, as long as aware of the hazard and compensate for it. Adjust gait: slow down, shorten stride, and walk "flat-footed". Most SAF occur when a pedestrian encounters an unexpected, localized area more slippery than the surrounding surface.

27 SLIP RESISTANCE Force that resists the tendency of the shoe or foot to slide on the walking surface. Affected by: Floor material and its finish Surface contaminants Footwear Gait

28 SLIP RESISTANCE Walking surfaces are considered slip resistant if there is adequate friction to prevent slipping while walking with reasonable care under expected use conditions. Higher the COF, less likely there will be a slip.

29 SLIP INDEX (Coefficient of Wet and Dry Friction) To be safe slip index should be.5 for level surfaces.8 for ramps or other inclined surfaces

30 Friction at Heel Strike If know frictional force at heel strike can estimate step length needed to slip and fall. A is hip flexion angle

31 Trip and Fall (TAF) Cause: dorsal foot, anterior ankle, or shin catches on an object in walking path or stair and is abruptly stopped Upper body continues forward, with resultant forward fall

32 CAUSES OF TRIPS Uneven walking surfaces, especially if unmarked and/or poorly lit. walkway level changes carpet/floor mat problems parking lot speed bumps

33 CAUSES OF TRIPS Unequal height of steps, especially one with unusually high rise Obstructions Box in store aisle Etc.

34 Step and Fall Cause: foot enters an unexpected: hole in, failure of, lower, or uneven walking surface

35 Examples Step and Fall missing manhole cover in street plywood covering a hole breaks Defect on stair tread Step down off curb in dark Step on stone on sidewalk

36 Stump and Fall Cause: moving foot encounters an obstruction or impediment in the walking surface

37 Stump and Fall Examples: Stub toe on bedpost Power cord run between two cubicles Protruding brick in brick sidewalk Door jamb higher than surrounding floor Sticky or tacky area

38 SLIPS

39 SLIPS Cause 40-50% of falls More often same level falls than from heights

40 Base of Support To stand, walk, run, climb stairs, etc. without falling must maintain COG over a base area. When standing, base is the normal footprints. Both COG & location, shape, and size of the base change with the activity. From Hyde, AS. Accidental Falls: Their Causes & Their Injuries

41 Base Base constantly moving when walking. We continually move body parts to maintain COG over base and maintain balance. Fall occurs when COG moves outside base of support

42 Slip and Maybe Fall If there is a failure of traction between a foot and walking surface, generally due to an unexpected contaminant or lubricant, pedestrian reflexively attempts to recover equilibrium. If can't fall

43 Slips When Walking 2 Types: At heel strike heel slips forward, and person falls backward At toe off, toes-forefoot slip backward fall

44

45 Why Do Falls Occur? Problem with: Environment Person Both

46 Environmental Problems Contributing to Falls Walking surface Slippery Defective in some manner Lighting Dark Sudden change from bright to low light or vice versa Distractions

47 Coefficient of Friction COF: 0.5 considered slippery Examples: 0.5 considered safe Leather soles on ice or a wet or oily smooth surface, e.g., ceramic tile - COF as low as 0.1 Dry brushed concrete surface and rubber heel - COF 1

48 Slip resistance (SR) of Floor Materials Proportional to surface roughness Sandpaper has high SR, glass low SR With a lubricating contaminant, e.g., water or oil, the microscopic projections from the surface (asperities) must be tall and sharp enough to extend up through the film of lubricant to engage the heel and sole of the shoe.

49 Lighting problems predisposing to STF Too dark walking surface should be evenly illuminated and have brightness level of at least 20 foot candles Too bright (glare) Too much or too little contrast contrast (ratio of dark to light) should be no less than 3-1 and no more than 20-1

50 Personal Problems Contributing to Falls Inattentiveness (not watching where you're going) Failure to use handrails Carrying large object obstructing view Wearing sunglasses in low-light areas

51 Personal Problems Contributing to Slips Improper footwear Walking fast or running higher shear forces at heel strike and toe off need higher coefficient of friction to prevent slip Rapid change in direction also requires higher COF

52 Footwear (Shoes and Boots) Use proper footwear for the environment Work shoes or boots should have slip-resistant soles and heels

53 Danger! Minimal heel-tosurface contact Other shoe problems: Leather or other hard, smooth soles Taps on heels

54 Physical Impairments Predisposing to STF Balance problems CNS or vestibular pathology alcohol or other drugs Decreased vision Impaired proprioception Decreased peripheral sensation Muscle weakness

55 Not all slips cause falls If a foot slips, is malpositioned, or steps on a foreign object the COG may shift outside the base. Response is to shift body parts in attempt to regain balance. If can't shift COG back over base fall.

56 Fall Direction Slips Slow or normal gait - fall backward or sideways, often landing on buttocks or hip, respectively Trip or stump and fall Fall forward Step and fall Usually forward Medial foot steps on higher surface than lateral, e.g., stone or edge of sidewalk ankle inversion fall forward and to same side, and vice versa

57 Possible Causes of Injuries from STF Torsion, bending, or sudden muscle contraction during recovery (actual or attempted) from slip or trip Strike an object during fall Upon landing after fall

58 CAUSATION ANALYSIS

59 CAUSATION ANALYSIS 2 step process, determining and documenting: what occurred in a given incident why it occurred

60 DETERMINING WHAT OCCURRED IN STF Patient/claimant history Statement(s) of witness, supervisor, and/or property owner/manager Report(s) from police officer, accident reconstructionist, biomechanist, or other investigator Medical evidence: EMT, physician chart note, radiology report, etc.

61 DETERMINING WHY STF OCCURRED First 3 data sources still apply: patient/claimant witness, supervisor, owner/manager police and/or other investigator

62 DETERMINING WHY STF OCCURRED But beware subjective evidence from persons involved in the incident Look for physical evidence that is measurable, verifiable, and unbiased.

63 DETERMINING WHY STF OCCURRED Generally physicians shouldn't opine on why Lack education, training, and experience in accident reconstruction Usually lack witness statement, investigator's report, etc. Hence database limited to patient history, physical findings, and test results. Patient history is always incomplete; and sometimes inaccurate or even fraudulent Physical findings may exaggerated or fabricated Trier of fact (judge or jury) decides liability

64 INTERVIEWING Interview should gather enough history to understand the reported mechanism and magnitude of injury. You re there when you can visualize the entire claimed incident in your head like a video clip in slow motion.

65 ANALYSIS OF HISTORY Are the mechanism & magnitude of injury reported consistent with: physical evidence? laws of physics prior histories? medical literature regarding known causes of trauma sustained?

66 ANALYSIS OF PHYSICAL AND TEST FINDINGS Is there objective evidence of injury consistent with reported mechanism and magnitude?

67 Analysis of Slips & Falls Were the motions which reportedly occurred and area(s) of body impacted consistent with what would be expected in the given circumstance?

68 INVESTIGATION

69 Investigation Slip Interview victim Measure: Slip-resistance of the floor Light intensity Contrast Assess floor care

70 How Get COF? Tribometry is the science of friction measurement COF measured by: dragging or pushing object across floor Striking floor with shoe materials (heel and sole) having known slip characteristics

71 English XL Variable Incidence Tribometer Angled cylinder applies force to sensor pad with gas pressure, not gravity. Sensor pad impacts test surface at angle, having horizontal as well as vertical velocity.

72 CASE STUDIES

73 Case Studies Most claims are legitimate Some aren't

74 Polio and Pop Don't Mix Elderly female with LLE atrophy and brace due to polio walked with cane. On a bright day she walked into restaurant with subdued lighting and windows tinted to cut light transmission. Light at floor level less than 20 foot candles. Needed 3-5 seconds for eyes to adjust to light. Contrast between brown ceramic tile and a spilled cola drink was too low for her eyes to perceive.

75 Polio and Pop Don't Mix Woman's right foot slipped to the right, and she fell with a resultant hip fracture. Investigation revealed the pores of the normally safe unglazed ceramic tile were packed with soap residue which became slippery when wet.

76 The Man Who Needed a New Hip 53-yr-old male w/ past history IV drug abuse and septic arthritis of L hip needed THR Worked as clerk in a grocery store without health insurance Claimed an unwitnessed slip on water in restroom while walking from toilet to sink, with a resultant fall and hip injury

77 New Hip 2 When SAF reported, store manager noted claimant's clothes weren't wet. Immediately inspected the restroom, found no water on floor. Suspicions aroused, called accident reconstructionist to investigate.

78 New Hip 3 Scene inspection revealed a small restroom, only 48" between toilet and sink. Floor had excellent friction; even wet slip index was Man was tall, lower limb length of 33". How long would his step need to be to break traction and have a heel slip?

79 New Hip 4 Necessary step length over 41". Is this reasonable for moving about inside a small restroom? When confronted with the forensic evidence, the employee withdrew his claim and quit.

80 The Cook that Slid into Home Plate Cook walked from restaurant into kitchen Slipped & fell at X Slid 8.5' across kitchen floor until hit plumbing under sink

81 Cook 2 Manager requested investigation Measured slip index floor.50 How fast would he have to be walking to slide 8.5'?

82 Cook 3 Velocity = 2ad With a slide distance of 8.5', and slip index of 0.50: 2 x 32fps x.5 x 8.5ft = 16.5 fps Normal walking speed 3-5 fps Is 16.5 fps plausible?

83 Fall Down Flight of Stairs Female clerk in police dept Responsible for maintaining evidence locker in basement Fired for making unauthorized long distance calls Later that day claims an unwitnessed fall down the stairs to basement

84 Fall Down Stairs 2 Reportedly fell from the top step to the landing below without striking any intervening steps since the fall was so sudden

85 Fall Down Stairs 3 She could not describe the cause of her fall, whether a trip or a slip.

86 Fall Down Stairs 4 After landing on the floor she struck her head against the wall beyond. Co-workers heard scream, hurried to basement, found her "semiconscious" on the floor with videotapes scattered about. She complained of diffuse pain but had no visible injuries.

87 Fall Down Stairs 5 Fall height 7' Carry distance 9' No contact from top to landing Plausible mechanism of injury?

88 Fall Down Stairs 6 What is the minimum walking velocity necessary for the woman to travel forward 9' while falling 7'? Time for the fall:.66 seconds. Required take off velocity = 9' /.66 sec = 13.6 fps (9.3 mph)

89 Fall Down Stairs 7 However, this calculation assumes she was walking horizontally What if the claimant had begun descending the stairs? Both the direction and speed of the velocity vector change

90 Fall Down Stairs 8 Average speed descending stairs is 3.2 mph for females & 3.7 for males. If the woman were going downstairs at the 37 angle indicated by the stair geometry, take off velocity would have to be 65 mph.

91 SUMMARY

92 Learn as much as you can about STF's they're common Gather as much data as possible about a specific STF Hopefully you can formulate an educated opinion on whether the reported mechanism of injury is plausible or not If you can't, decline to render or qualify opinions on causation

93 REFERENCES Andres, R.O., O'Conner, D. And Eng, T. (1992) "A practical synthesis of biomechanical results to prevent slips and falls in the workplace" in Kumar, S. (Ed), Advances in Industrial Ergonomics and Safety IV, Proceedings of the Annual International Industrial Ergonomics and Safety Conference, London: Taylor & Francis, pp Chaffin, D.B. and Andersson, G.B.J. (1984) Occupational Biomechanics, John Wiley & Sons, New York. Courtney TK, et al: Occupational slip, trip, and fall-related injuries-can the contribution of slipperiness be isolated? Ergonomics 2001 Oct 20, 44(13):

94 REFERENCES Dutton, Cheryl. "Make Foot Protection a Hit," Safety and Health, Vol. 138, No. 5, November, Pp Ellis, J. Nigel and Howard B. Lewis. Introduction to Fall Protection. American Society of Safety Engineers, Gage, JR: An overview of normal walking. Instructional Course Lectures, 39, , Goldsmith, Aaron. "Natural Walking, Unnatural Falls," Safety and Health, Vol. 138, No. 5, December, Pp Lehtola CJ, Becker WJ, Brown CM: Preventing Injuries from Slips, Trips and Falls, available online.

95 REFERENCES Miller, Barrett C: Investigating Slips and Falls: The Complex Dynamics Behind Simple Accidents, available online. Peter, Robert: "Fallsafe: Reducing Injuries From Slips and Falls," Professional Safety, Vol. 30, No. 10, October, Pp Peter, Robert: "How to Prevent Falling Injuries," National Safety and Health News, Vol. 132, No. 4, October, Pp Strachta, Bruce J. "Keep Fall Costs Down," Safety and Health, Vol. 135, No. 4, April, Pp Waller, Julian A. Injury Control: A Guide to the Causes and Prevention of Trauma. Lexington Books. 1985