Low Back Injuries

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Low Back Injuries

• TM 655
• Summer 2008
• Carter J. Kerk, PhD, PE, CSP, CPE

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Outline

• Concepts
• A Systems Approach
• Risk Factor Model
• ID, Evaluation, Control
• Identification Checklists
• Evaluation
• Force
• Posture
• Repetition

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Stover Snook

• At any time, 15 to 20 of adults, evenly split
  between men and women, experience low back
  symptoms.

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Stover Snook

• 35 of adults say theyve had low back pain in
  the past month, 50 in the last year.

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Stover Snook

• About two-thirds of all back pain develops
  gradually without any trauma or precipitating
  event.

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US Bureau of Labor Statistics

• For employees who miss work time due to back
  problems, the median time away from the job is
  between 6 and 7 days.

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National Research Council

• In the US, employers in private industry report
  around 7 million cases of work-related
  musculoskeletal injuries each year, with 25 of
  these leading to lost working days and restricted
  activities. It is estimated that 5 to 6 million
  of these cases are work-related back pain leading
  to 100 million working days lost.

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Risk Factor Model for Potential Development of
Cumulative Trauma Disorders,Including Low Back
Pain
Lack of Rest
Work/Rest Ratio
Shift Length
Environment
Sustained
Repetition
Occupational
Vibration
Non-Occupational
Temperature
Posture
Physical Temporal Risk Factors
Force
Personal
Psychosocial
Compounding Risk Factors
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Attacking Hazards

1. Identification
2. Evaluation
3. Control

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Control of Hazards

1. Engineering Controls
2. Administrative Controls
3. Personal Protective Equipment

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Identification

• Body Part Discomfort Survey
• Quick Exposure Checklist (QEC)
• Pareto Analysis

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Body Part Discomfort Survey

• Ask employee to shade in areas of discomfort
• Rate each shaded area on a scale

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Quick Exposure Checklist (QEC)

• Quickly assess the exposure to risks for
  work-related musculoskeletal disorders
• See http//www.geocities.com/qecuk

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Quick Exposure Checklist (QEC)

• Steps
• Self-Training
• Observers Assessment Checklist
• Workers Assessment Checklist
• Calculation of Exposure Scores
• Consideration of Actions

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Quick Exposure Checklist (QEC)

A1
A2
A3
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Quick Exposure Checklist QEC

Observer Assessment
Worker Assessment
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Quick Exposure Checklist QEC

E() X/Xmax x 100
QEC Score (E) ACTION
40 Acceptable
41 50 Investigate Further
51 70 Investigate further and change soon
gt70 Investigate and change immediately
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Use of Checklists

• Preliminary screening
• Before and after analysis
• Relative comparison among tasks

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Pareto Analysis

• The Powerful Few - Group A 10 of the tasks
  produce 70 of injuries focus on these
• The Insignificant Many - Group C 65 of tasks
  produce lt10 of injuries

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Evaluation of Force

• Direct force measurement
• Force gauge, scale
• NIOSH Lifting Guide
• Psychophysical Tables

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NIOSH Lifting Equation

• Recommended Weight Limit
• Load that nearly all healthy workers could
  perform over a substantial period of time without
  an increased risk of developing lifting-related
  low back pain
• RWL LC x HM x VM x DM x AM x FM x CM
• Lifting Index
• Estimate of physical stress
• LI Load Weight / RWL

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NIOSH Lifting Equation

• RWL LC x HM x VM x DM x AM x FM x CM
• LC 51 lb 23 kg
• HM Horizontal Multiplier
• VM Vertical Multiplier
• DM Distance Multiplier
• AM Asymmetric Multiplier
• FM Frequency Multiplier
• CM Coupling Multiplier
• Each multiplier ranges from 0 to 1

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NIOSH Lifting Equation
Determination of H and V

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NIOSH Lifting Equation
Determination of Asymmetry (A)

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NIOSH Lifting Equation

• Does Not Apply When Lifting or Lowering
• One hand
• Over 8 hours
• While seated or kneeling
• In a restricted work space
• Unstable objects
• While carrying, pushing, pulling
• Wheelbarrows, shovels
• High speed (gt30 inches / sec)
• Slippery floors

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NIOSH Lifting Equation

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NIOSH Lifting Equation

• Horizontal Multiplier
• Metric
• HM 25/H
• US Customary Units
• HM 10/H
• Or Use Table 1

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Evaluation of Force

• Direct force measurement
• Force gauge, scale
• NIOSH Lifting Guide
• Psychophysical Tables

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Psychophysical Tables

• How much should a worker be required to lift or
  lower or push or pull or carry?
• How much is too much?
• These tables are the culmination of 25 years of
  experiments at the Liberty Mutual Research Center

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Psychophysical Table Lifting, Males

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Psychophysical Table Pushing, Females, Initial
Force

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Evaluation of Posture

• Photography / Videotaping
• RULA
• Rapid Upper Limb Assessment
• REBA
• Rapid Entire Body Assessment

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Photography / Videotaping

• Capture and evaluate entire work cycles
• Freeze frame postures
• Measure body angles
• Protractor / Goniometer
• Combine with force measurement
• Combine with frequency evaluation

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RULA

• Rapid Upper Limb Assessment
• Used to assess the posture, force, and movement
  associated with sedentary tasks
• Including computer workstation tasks,
  manufacturing and retail tasks where the worker
  is seated or standing without moving about

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REBA

• Rapid Entire Body Assessment
• Whole body
• Posture is static or dynamic
• Frequent or infrequent load handling

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REBA

• Steps
• Observe the task
• Select the postures for assessment
• Score the postures
• Process the scores
• Establish the REBA score
• Confirm action level and urgency

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REBA

• Selecting postures for assessment
• Most frequently repeated postures
• Longest maintained postures
• Posture requiring greatest forces
• Posture known to cause discomfort
• Extreme, unstable, or awkward postures

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REBA

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REBA Trunk Scoring

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REBA Neck Scoring

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REBA Leg Scoring

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REBA Scoring Group A

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REBA Load / Force Score

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REBA Action Levels

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Evaluation of Repetition

• Tools Stopwatch, Videotape
• Methods Work Measurement Skills
• Calculate repetitions e.g., lifts per minute
• Document the work cycles

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Biomechanics

• Advanced Technique
• Uses elements of analysis from
• Force and Posture
• Requires knowledge of
• Anatomy, Anthropometry, Statics, Dynamics

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Gender and Posture Differences

• Strength testing shows there are significant
  differences in lifting capability due to gender
  and posture
• These concepts are critical in job analysis and
  job design

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Squat Lift vs. Stoop Lift

• Normally a squat lift is recommended over a stoop
  lift - Lift with your legs, not your back

• But, if you cannot fit the load between your
  knees then a stoop lift becomes less stressful
  than a squat lift

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Lifting Analysis

• This type of analysis helps to understand the
  strength required throughout the lift at the
  elbow, shoulder, and hip.
• The most stressful points can be identified.

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Simple Forearm Model

• With a simple biomechanical model of the forearm,
  you can estimate the elbow flexion strength
  necessary to support a load at the hand.

• This information can be useful in evaluating
  stressful tasks or in designing new tasks.

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Low Back Modeling

• There are also biomechanical models of the forces
  and moments in the low back.
• This simple 2D model includes compression and
  shear forces in the spine, as well as muscle
  forces and abdominal forces.
• This model helps to demonstrate the importance of
  minimizing the moment arm (or lever arm) from the
  low back to the hand grip. Keep the load close
  to the body!

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Engineering Controls

• First, analyze the job
• Surveys, checklists, evaluation of risk factors
  (force, posture, repetition, etc.), pareto
  analysis
• Attack high-risk tasks first
• Look for low hanging fruit

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Engineering Controls

• Most desirable approach
• Redesign or Modify
• Workstation
• Tools
• Work Methods
• Fit the worker

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Engineering Controls

• Establishing optimal work methods
• Adjustable workstations
• Tilt bins or containers
• Tool balancers
• Conveyors, Turntables
• Jigs, Fixtures
• Rounded or padded edges on worksurfaces
• Mechanical assist devices
• Selection of ergonomic tools

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Work Surfaces

• Adjustability
• Ease of Adjustability
• Avoid sharp edges
• Consider sit/stand options

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Placement Storage of Materials

• Consider frequency and weight
• Store heaviest and most frequent at knuckle
  height, Power Zone
• Power Zone Knuckle to Elbow Height, Close to
  Body
• Store medium items from knee to shoulder
• Store only light items below knee or above
  shoulder

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Work Station Accessories

• Arm rests
• Wrist rests
• Foot rails and foot rests
• Document holders

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Engineering Controls
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Engineering Controls
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Controls

• Engineering Controls
• Administrative Controls
• Personal Protective Equipment

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Administrative Controls

• Secondary to Engineering Controls
• Insure proper methods are used
• Effective maintenance housekeeping
• Proper use of tools equipment
• Employee conditioning
• New employee conditioning

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Administrative Controls

• Limiting overtime on high risk jobs
• Ensuring adequate rest breaks
• Job rotation
• Job enlargement (cross-training, flexibility)
• Teaming
• Reduce production rates
• Last resort

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Microbreaks

• What is a microbreak?
• Take them frequently

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Standing Fatigue Interventions

• Proper footwear
• Shoe inserts
• Anti-fatigue mats
• Foot rails
• Promote good lower extremity circulation
• Yes, this affects low back pain!

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Hazard Prevention Control

• Engineering Controls
• Administrative Controls
• Personal Protective Equipment

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Personal Protective Equipment

• After engineering administrative controls are
  exhausted
• Gloves
• Finger cots
• Arm guards
• NOT PPE
• Braces, splints, back belts or lifting belts

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Wrist Splints
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Lifting

• Power Zone
• Squat lift generally better than stoop
• Bend with your knees, not your back
• Keep the load close
• Love Your Load
• Get a good hand hold
• Move slowly, no jerks allowed
• Know or test the load
• Label loads
• Avoid twists

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More Lifting Tips

• Get help (from a person or an assist device)
• Eliminate lifts
• Reduce loads
• Store properly
• Get a strategic delivery
• Use proper technique on light loads