2. Definition
• Musculoskeletal disorder (MSD) is an injury or disorder of the
muscles, nerves, tendons, joints, cartilage, and spinal discs.
• It is not an acute injury, rather a chronic disease which
develops over time.
• MDS is related to manual tasks
• It has been recognized as a source of significant pain,
disability and disadvantage for the injured person and a
substantial burden on modern societies. Statistics suggest
that more than 30% of all occupational injuries are
musculoskeletal injuries associated with manual tasks
(Straker et. al. 2004).
• Statistical data for MSD in US from USDOL – BLS
(http://stats.bls.gov/news.release/pdf/osh2.pdf)
3. Magnitude of the problem in
occupational context
• MSD burden on US economy in 1994
equaled $3.6 billion in direct worker
compensation, total cost $10.8 billion with
$12,000 per case
• Approximately 260,000 carpal tunnel
release surgeries are performed each
year, with 47% of cases are considered to
be work-related.
4. Work related musculoskeletal
disorders (WMSD)
• Various synonyms of WMSD - RSI (repeated strain
injury), CTD (cumulative trauma disorder), Over use
syndrome etc.
• Relationship between physical exposures in occupations
and WMSD has been noted by an overwhelming number
of previous studies.
• Due to repeated straining body tissue and not allowing
enough time to heal are believed to cause progressive
discomfort, pain, and ultimately disability to continue
regular work.
5. Factors believed to be associated
with WMSD
• Repetition/duration/rest – short cycle time (<30
sec)
• Static work
• Joint deviations – awkward postures
• Velocity and acceleration- speed of movement
• Internal forces on joints
• Vibration
• Coldness
• Non occupational factors – fitness level, mental
stress, smoker, hobby.
6. Hand and wrist
Carpal tunnel syndrome
is caused by swollen and inflamed tissue
that puts pressure on the median nerve,
which provides sensation to all fingers of
the hand except the little finger. The
median nerve runs from the forearm into
the hand through the carpal tunnel in the
wrist. Symptoms usually start gradually
with a vague ache in the wrist that runs into
the hand or up the forearm. Eventually,
there can be:
Tingling or numbness in the hand or fingers, especially the thumb, index,
middle or ring fingers, but not the little finger. This sensation often occurs
while sleeping or after using the hand. Pain radiating or extending from the
wrist up the arm to the shoulder or down into the palm or fingers, especially
after forceful or repetitive use. A sense of weakness in the hands; dropping
objects. A loss of feeling in some fingers.
Credit of this page on CTS goes to
website provided by Mayo clinic,
Florida
7. Elbow, Shoulder, neck
• Tennis elbow – Lateral epicondylitis: strong gripping with
extended elbow, sudden or repetitive use of arm.
• Golfer’s elbow – Medial epicondylitis
• Cubital tunnel syndrome: Ulner nerve compression
where it crosses the elbow. Pain that occurs when hitting
funny bone.
• Thoracic outlet syndrome- symptoms include neck,
shoulder, and arm pain, numbness.
• Rotor cuff syndrome – inflammation of shoulder tendons
• Bursitis – inflammation of bursa (fluid filled sacs) in either
elbow, shoulder or knee.
8. Ergonomic Prevention Approach
• Engineering approach – Analyze the job it detail. Video tape
the job, various posture evaluation schemes (MANTRA,
RULA, REBA, OWAS, JSI)* can be used for rough estimation
of joint deviation, repetition/duration, and forces involved.
They provide scores for action limit and maximum limits, by
which jobs can be selected for improvement.
• Internal joint forces can be evaluated by EMG, biomechanical
models.
• Solution approaches are automation, mechanization, job
enlargement, redesign the workstation for adjustability and
better working posture, better method to do the work to
reduce force, duration, repetition.
• Administrative approach – Job rotation, use of part time
workers, exercises, stress reduction.
9. Examples of engineering solutions
• Counter balance and suspend hand tools - reduce static
load of holding the tool.
• Tilt the work surface, tilt fixture - facilitate better posture,
viewing, reach
• Replace keying in by barcode, provide bioptic scanners,
provide portable scanners –reduce repetitive motions
• Provide hand tools with correct grip style/diameter/texture
– reduce gripping force, improve wrist posture
• Maintain sharpness of the knives – reduce force required
to cut Hand tools are properly maintained - reduce
vibration
10. More of engineering solutions
• Use correct work height – better upper body and hand-
arm posture
• Limit reaching motions to minimum - better upper body
and hand-arm posture
• Lower the work area if shoulders needed to be lifted -
better hand-arm posture
• Provide arm rest if elbows are needed to be raised –
reduce static load at shoulder
• Consider sitting/standing/sit-stand work posture – reduce
static load in lower back, promote change of torso posture
• Arrange workplace to minimize twisting, forward or lateral
bending – reduce harmful posture of torso
• Correct viewing angle - minimize static load on neck
muscles, eye strain.
11. Posture targeting and recording
tools
• Most of these tools are developed to quickly identify
tasks that have high risk of MSD. These tools are easy to
learn and can be used in participative ergonomics
approach.
– RULA (Rapid Upper Limb Assessment)
– REBA (Rapid Entire Body Assessment)
– Job Strain Index (JSI)
– Quick Exposure Checklist (QEC)
– Manual Task Risk Assessment Index (ManTRA)
– OWOAS (Nordik tool for whole body posture assessment)
– Check Prof. Alan Hegde’s Cornell Uuniversity Ergo web site for
details of these tools. http://ergo.human.cornell.edu/cutools.html
