Musculoskeletal Disorders (MSDs)

by Pourya Amiri

Musculoskeletal disorders (MSDs) are one of the causes of absenteeism at workplaces in Canada. Roughly 10% of Canadian adults had a repetitive strain injury (RSI) serious enough to limit normal activities. Also, 2.3 million Canadians aged 20 and up reported having RSI in the previous year.

This article tries to define MSD, the main hazards that increase the risk of MSDs and the mechanism of injury.

What is MSD?

Musculoskeletal disorders are disorders and injuries affecting the musculoskeletal system, including muscles, tendons, ligaments, joint systems, nerves, etc.

MSDs do not include musculoskeletal injuries or disorders that directly result from incidents, violence, etc.

MSDs are also known by such other terms as:

• Repetitive Strain Injury (RSI)
• Work-related Musculoskeletal Disorder (WMSD)
• Cumulative Trauma Disorder (CTD)
• Occupational Overuse Syndrome (OOS)

MSDs can have any or a combination of the following symptoms:

• Pain
• Weakness
• Fatigue
• Burning
• Swelling
• Tenderness
• Cramps
• Tingling
• Numbness
• Pins and Needles
• Stiffness
• Reduced Range of Motion

Common examples of MSDs include:

• Carpal Tunnel Syndrome
• Hand Arm Vibration Syndrome (HAVS)
• Low Back Pain
• Rotator Cuff Tendinitis
• Tennis Elbow
• Tension Neck Syndrome
• Thoracic Outlet Syndrome
• Trigger Finger

Hazard Factors Contributing to the Risk of MSDs

Primary Hazards

MSDs Primary hazards include:

• Force
  The higher the force applied to the body organs, the higher the risk of MSD development.
• Repetition
  Frequent forces, even low in magnitude, cause fatigue in the body organs, leading to MSD over time.
• Posture
  Poor posture leads to an increase in the applied force and, therefore, increases the risk of MSDs.

Other Hazards

Secondary hazards contributing to the risk of MSDs include, but are not limited to:

• Contact Stress
  Continuous stress applied to the organs at the contact points (e.g. leaning against surfaces) increases the risk of MSDs.
• Vibration
  Vibration is a repetitive low force applied to the organs that lead to MSDs.
  There are two categories of vibration:
  • Hand-Arm Vibration:
    e.g. vibration resulting from the operation of handheld rock drills
  • Whole-Body Vibration
    e.g. vibration due to the operation of dump trucks
• Cold / Hot Temperatures
  Extreme cold and hot temperatures also increase the risk of MSDs such as trigger fingers.
• Hammering with Hand / Knee
  Continuous use of hands and/or knees to hammer objects increase the risk of MSDs.

Mechanism of Injury

Organ Force Tolerance

The human body consists of various tissues with different capacities to resist compressive and tensile stress, whether external or internal. Besides, the tolerance limit of the same organ of different people may vary according to their age, body shape, general health condition and other factors.

An organ fails if the applied force is greater than its tolerance limit.

Tolerance vs. Time

Organs’ tolerance reduces over time due to fatigue. That’s why holding or lifting a small weight becomes more challenging after some time, even if the weight is well below the tolerance limit of our body.

Low, Continuous Force

As the tolerance reduces, even a low-magnitude force becomes critical over time and eventually causes the organ to fail.

Low, Repetitive Force

Tolerance drops faster (due to fatigue) should the organ is exposed to repetitive forces.

Posture vs. Force

Poor posture increases the applied force to the organs due to the leverage effect.

Conclusion

Musculoskeletal disorders play a big role in creating health issues that can affect the quality of our lives. As such, it is important not to overlook the risk of MSDs in the Job Hazard Analysis by evaluating the so-defined primary and secondary hazards in any job involving human interactions.

Reference

PSHSA – Public Services Health and Safety Association Website