Slips, Trips, and Falls - Lecture Notes

Lecture 16: Slips, Trips, and Falls

Learning Objectives

  • Define a slip, a trip, and a fall.
  • Understand the consequences of falls.
  • Describe factors associated with slips (e.g., friction).
  • Explain the mechanisms of a slip and how we may adapt to prevent slips.
  • Describe the causes of tripping and strategies to prevent falls.
  • Describe and define osteopenia and osteoporosis in relation to fall risk and consequences of falls.
  • Describe some interventions to slow the progression of osteopenia and osteoporosis.

Definition of a Fall

  • A fall is defined as “an event which results in a person coming to rest inadvertently on the ground or floor or other lower level, excluding intentional change in position to rest on furniture, wall or other objects”.
  • Usually the result of a slip or a trip.
  • Source: World Health Organisation.

Statistics on Falls

  • Falls are the second leading cause of accidental or unintentional injury deaths worldwide.
  • Falls injuries are the 2nd leading cause of unintentional death (after road accidents) and are the major precursor to death in the elderly (WHO, 2002).
  • Each year an estimated 424,000 individuals die from falls globally, of which over 80% are in low- and middle-income countries.
  • Adults older than 65 suffer the greatest number of fatal falls.
  • 37.3 million falls that are severe enough to require medical attention occur each year (World Health Organization, 2016).
  • Falls are “the most common mechanism of injury and endure as a persistent risk to morbidity and mortality across all ages” (James et al., 2020).
  • People aged 65 and over spend 4 million days per year in hospital as the result of falls and fractures (Royal College of Physicians, 2011).
  • One third of over 65s fall once a year, and in 35 years time more than ¼ of us will be over 65 (Age UK).
  • Prevention strategies should emphasise education, training, creating safer environments, prioritising fall-related research and establishing effective policies to reduce risk.
  • Falls are estimated to cost the NHS £4.6 billion per year (Age UK).
  • In 2008 in Wales, 2599 injuries resulted from slips, trips and falls costing Welsh taxpayers £41.5 million.

Functional Capacity and Age

  • Functional capacity changes over a lifetime, from growth and development in early life to maintaining independence and preventing disability in older age.
  • Changes in the environment can lower the disability threshold.
  • Assistive devices provide the potential to increase the level of function for all age groups.

Causes of Slips: Insufficient Friction

  • Complex matrix of interactions – intrinsic and extrinsic.
  • Workplace & Public Spaces – flooring materials.
  • Signage warning wet floors = change gait.
  • Footwear has a significant effect.
  • ‘Frictional Coefficient’:
    • Dimensionless number describing the ratio of the force of friction between two bodies and the force pressing them together.
    • A slip occurs at the shoe-floor interface when the friction required (required coefficient of friction, RCOF) to support walking exceeds the friction available (available coefficient of friction, ACOF).
  • Floor slip resistance testing.
  • The science of measuring coefficient of friction of flooring surfaces.

Shoe-Surface Interactions

  • Factors influencing slip potential:
    • Shoe
    • Human
    • Surface
    • Floor Material
    • Cleaning
    • Environment
    • Contamination
    • Use
    • Footwear
    • Behaviour

Friction

  • Friction - The resistance relative to the movement between a surface and an object in contact with that surface
  • Static Friction:
    • Applied force < Frictional force
  • Kinetic Friction:
    • Applied force > Frictional force

Gait and Slipping Adaptations

  • Adaptation to a slippery surface:
    • Aim to place sole of foot vertically on the ground.
    • Increase arm motion.
    • Increase trunk lateral motion.
    • Aim to stabilise hip and COM over the supporting limb.

Shoe Tread and Slip Risk

  • Tread affects contact area.
  • \downarrow Friction \implies Slip risk

Floor Slip Resistance Testing

  • Public flooring surfaces must have a minimum friction coefficient rating relative to most shoe soles.
  • UK have R ratings, recommended by Health and Safety Executive (HSE).
  • Determine the slip resistance of a surface to determine whether it is appropriate for a given floor.
  • Pendulum tests can give you frictional coefficient readings for different surfaces or PTV values (pendulum test values).
    • 0-24 = high slip potential
    • 25-35 = moderate slip potential
    • 36+ = low slip potential
    • This changes for ramps

Causes of Trips: Unanticipated Gait Disruption

  • The primary cause of falls is tripping due to unanticipated foot contact with grounded objects.
  • These cause instability from which an individual is unable to recover.
  • A large volume of research has been conducted to understand the mechanisms.
  • Elderly at greatest risk – reaction times to falling and diminishing strength

Trip and Brain Reaction

  • There’s a lag between our brain registering that we’re about to fall, and our muscles reacting to the fact that we’re falling.
  • The brain recognizes a loss of balance before the fall actually occurs.

Gait Mechanics

  • Gait Cycle:
    1. Initial Contact
    2. Loading Response
    3. Mid-Stance
    4. Terminal Stance
    5. Pre-Swing
    6. Initial Swing
    7. Mid-Swing
    8. Terminal Swing

Gait Mechanics and Trips

  • Minimum toe clearance (MTC) = point of minimum separation between the ground and toes during forward swing
  • MTC = most important kinematic consideration in clinical gait assessment regarding tripping risk
  • MTC also coincides with peak forward velocity in the swinging foot
  • This is when the risk of tripping is greatest as it is also when the forward-travelling centre of mass moves in front of the base of support.

Trip Recovery Strategies

  • Elevating strategy
    • In response to an early swing phase perturbation, THREE kinematic changes will be likely to occur:
      • Flex swing leg joints
      • Extend stance leg joints
      • Raise CG
    • Centre of mass is moving forwards – early in the swing phase people will adopt elevating strategy
    • flex swing leg at hip, knee and ankle and extend the stance leg at same joints to raise the centre of gravity to clear whatever the perturbation was
    • Elevation = Early
  • Lowering strategy
    • In response to a late swing phase perturbation
    • Rapidly lower swing leg and shorten step length
    • Lowering = Late
  • Falling Strategy
    • In response to a late swing perturbation
    • Elderly found to have insufficient limb strength, response time and movement speed to achieve large enough recovery step for elevating strategy when perturbed later in mid-swing

Trips: At-Risk Populations (Elderly)

  • Normal process of aging:
    • Speed decreases
    • Stride length shortened
    • Step length shortened
    • Time spent in double stance increases
    • Smaller swing to support phase ratio
  • Neuromuscular control – recent research has found differences in spatial and temporal coordination of muscles between people who fell and people who recovered from a trip perturbation (Sawers et al., 2017)

Trips: At-Risk Populations (Clinical)

  • Clinical populations with abnormal or clinical gait:
    • Cerebral palsy
    • Parkinson's Disease
    • Ataxia
    • Inactivity, obesity
  • Decreases in population physical activity:
    • Physical activity decreased by 50% between 6 and 16 years of age (USDHHS, 2000)
  • Recommendation for older adults at risk of falls should incorporate physical activity to improve balance and coordination at least three days per week

Biomechanical Tools in Fall Prevention

  • Motion Capture, 2D and 3D:
    • Kinematics during walking & in response to a trip
    • Automatic motion capture
    • Slow motion ability for closer analysis
  • Force Plate:
    • Loading patterns in gait
    • Stand-up sit down test to assess independence
  • EMG:
    • Muscle activity during walking & in response to a trip
  • Strength and Agility Screening:
    • 8 Foot Up and Go Test
  • Simulation Modelling:
    • Combining above data to make predictions
    • Applicable to ‘at risk’ populations

Application of Knowledge to Fall Prevention

  • Examples of interventions:
    • Strength training
      • Lower limb strength training improved functional gait kinematic measures (walking speed, stride length, toe clearance) associated with fall risk (Persch et al., 2009)
    • Real-time augmented ‘technique’ training
      • Minimum toe clearance was improved in older adults – it reduced their risk of a trip from once every 3 strides to once every 161 (Begg et al., 2014)

Osteopenia & Osteoporosis

  • Osteopenia:
    • Refers to a level of bone density below the normal level for the age and sex of the individual.
    • Osteopenia is said to be the bone’s physiological response to disuse
  • Osteoporosis:
    • Is a progression of osteopenia, where the bone cannot adapt to the loads imposed by them by their habitual mechanical usage
  • The four major variables which influence the onset and progression of osteoporosis are genetic factors, endocrine status, diet and physical activity (National Osteoporosis Foundation, 2016)

Major Variables Contributing to Osteopenia

  • Bone mineral density is lower than normal
  • Postmenopausal women – decrease in oestrogen
  • “The bone’s physiological response to disuse”
  • Absence of moderate habitual loading/lack of exercise
  • Poor diet
  • Excess alcohol consumption
  • Smoking
  • Long term glucocorticoid medications
  • (exposure to radiation – less common)
  • Young female athletes
    • Female athlete triad
    • Required to have lower body fat – sustained negative caloric balance
    • Amenorrhea – decrease in oestrogen levels
    • Eating disorders
  • Also common in coeliac disease
  • Osteopenia is regarded as a precursor of osteoporosis
  • Not everyone with osteopenia will develop osteoporosis

Biopositive and Bionegative Effects of Loading

  • Bionegative:
    • Rest homes
    • Space Flight
    • Post-Injury Immobility
    • Insufficient loading during childhood
    • Loading above tissue tolerance thresholds
    • Tissue failure
  • Biopositive:
    • Normal loading patterns
    • Regular weightbearing
    • Sports training
    • Weightlifting
    • Loading up to tissue tolerance thresholds

Major Variables Contributing to Osteoporosis

  • Age: older adults are at higher risk
  • Gender: women are at higher risk - postmenopausal
  • Genes
  • Ethnicity: people from black African-Caribbean /Pacific Island origin are at lower risk because they have bigger and stronger bones
  • Low body weight
  • Certain medical conditions: rheumatoid arthritis, thyroid conditions and conditions such as Crohn’s Disease that affect absorption
  • Certain medications: corticosteroids, some cancer treatments, anti-epileptic drugs
  • Lifestyle factors: smoking, alcohol, diet and exercise

Slowing Osteopenia: Interventions

  • In every age group physical exercise stimulates mineralization of the bone
  • Osteopenia most common in postmenopausal women – decrease in oestrogen levels
  • Remember Wolff’s Law – Bones adapt to mechanical loading
  • Regular training/weight bearing exercise throughout life can achieve higher peak bone mass
  • Weighted exercise has been found to slow or reverse osteopenia effects, even in older people ** with medical approval**
  • Progressive loading for musculoskeletal adaptation

Consequences of Falls with Osteopenia & Osteoporosis

  • Osteoporosis well known to increase risk of falls/fall-related injuries
  • ~10% of falls (community dwelling) result in serious injury, mostly fractures
  • After the onset of full osteoporosis, loading/exercise can be unsafe as bone is generally unable to carry the load applied and will break
  • Body weight generally increases with age, or stays the same but the weight of the skeleton decreases, making it more difficult to support the body for normal daily activities
  • Fractures occur with no, or very little trauma in osteoporotic bones
  • However, this is not the case in osteopenic bones – which is where movement specialists can be incredibly valuable
  • Wolff’s Law – gradual loading, supervised load-bearing exercise. Target particular areas
  • Compound and SAFE exercises

Assessments for Ability

  • Timed Up & Go Test (TUG)
    • Commonly used to assess functional mobility in retirement homes to classify dependence level and fall risk
  • Stand-Up Sit-Down Test
    • The sit to stand (STS) test is a physical function test proposed to evaluate fall risk in older adults
    • The only equipment necessary to do this are essentially a chair and a stop watch
    • This makes it possible to have a repeatable measure which is cost effective and convenient