Occupational Therapy & Ergonomics

• Lecture 5 covers Occupational Therapy & Ergonomics

Repetitive Tasks

• Repetitive tasks lead to pain and injuries.
• They can also exacerbate pain from other conditions.
• Repetitive tasks may have identifiable causes.

Specific vs Non-Specific WMSD

• Disorders either specific to an anatomical location or nonspecific
• Specific disorders are identifiable by their anatomical source.
• An example is carpal tunnel syndrome, trigger finger, and brachial plexus lesion.
• Non-specific disorders occur in non-specific anatomical areas.
• Patients often report diffuse, non-anatomical symptoms that affect nerves, tendons, and other anatomical structures.
• Symptoms include pain, discomfort, numbness, and tingling without clear pathological evidence.

Interventions for Musculoskeletal Issues

• Should address not only physical but also psychological and social factors
• Psychological considerations include anxiety, fear of reinjury, and general worries.
• Social considerations include social support and the ability to perform social roles.

Main Occupational Factors Associated with WMSDs

• Force is a key factor.
• Posture matters.
• Repetition of movements contribute.
• Duration of tasks is important.
• Stress and anxiety are factors.
• As the quantity of above factors associate grows, the risk for WMSDs increases.

Armstrong's Model of Developing WMSDs

• Exposure, dose, response, and capacity influence WMSDs.
• Exposure is the rate of exposure to work demands like posture, force, and repetition.
• Dose (effect) leads to muscle force production, tendon and ligament stretching, and joint compression.
• Primary response involves changes in tissue shape, cell death, or waste product accumulation in tissue.
• Secondary responses include pain, strength changes, mobility changes, loss of coordination, and discomfort.
• Capacity defines the musculoskeletal system's ability to cope with different doses.
• Mechanical factors such as soft tissue strength and bone density
• Physiological factors such as aerobic capacity
• Psychological factors such as self-esteem and tolerance to discomfort and stress

Injuries at Work

• Upper body injuries are more common than lower body injuries.
• Accidents involving hand tools are a frequent cause of upper body injuries.
• Other causes include overexertion, cuts, lacerations, strains, and sprains.

Tissue Pathomechanics (Muscle Pain)

• Muscle pain results from the accumulation of waste products in muscles.
• Pain causes cramps and muscle weakness or spasms.
• Prolonged repetition (handwriting, typing) or extreme posture are common causes.
• Pain onset occurs 12-24 hours after exposure.
• Pain typically peaks 1-3 days post-exposure.

Tissue Pathomechanics (Tendon Pain)

• Tendinitis is the inflammation of tendons.
• Tendon pain is caused by force, posture, and repetition.
• The combination of these factors increases the risk of injury.
• Increased repetition can increase blood supply to muscles but decrease it to tendons and ligaments, leading to pain.

Tissue Pathomechanics (Trigger Finger)

• Trigger finger is also known as stenosing flexor tendonitis.
• Results in stiffness and snapping of the finger.
• Due to the thickening of the fibro-osseous canal.
• Commonly found among workers requiring static grasping.

Tissue Pathomechanics (Bursitis)

• Bursae protect muscles and tendons from rubbing against bones during movements.
• Bursitis is the inflammation of the bursae due to overexertion or injury.
• It's most common among those performing on-knee tasks.
• Also occurs with prolonged weight bearing on joints.

Tissue Pathomechanics (Neuritis)

• Repeated or prolonged exertion damages the nerve supplying a muscle.
• Damage may also occur through the nerve passing through a muscle.
• Causes sensations of numbness or tingling in the body.

Tissue Pathomechanics (Bones and Joints)

• Repeated heavy loading is vital for bone formation and maintenance up to a limit.
• High repetition loading can cause stress fractures.
• Mechanical trauma can contribute to osteoarthritis by degenerating articular cartilage.

Tissue Pathomechanics (Neck Disorders)

• Related to neck flexion, arm force, arm posture, duration of sitting, static posture, trunk twisting, and workspace design.
• Because the center of gravity (COG) is anterior to the neck, the constant contraction of posterior neck muscles prevents the head from falling forward.
• The head should undergo no more than 15 degrees of flexion.

Tissue Pathomechanics (Carpal Tunnel Syndrome)

• Associated with forceful and repetitive work
• Entraps the median nerve and reduces blood supply to the nerve due to compression within the tunnel structures.

Tissue Pathomechanics (Tennis Elbow)

• Overexertion of wrist extensor muscles during activities requiring large grasping force.

Tissue Pathomechanics (Shoulder Disorders)

• Risk increases with shoulder abduction or flexion exceeds 90 degrees.
• Causes impingement or rotator cuff syndrome.
• Incidences increase with high work cycles.

Tissue Pathomechanics (Lower Limb Injuries)

• Walking with heavy loads or excessive use of the knees are the most common causes.
• Disorders include osteoarthritis and bursitis.

Risk Assessment for WMSDs

• Assessed by visual observation and measurements.
• Can be assessed by data of reported injuries.

Ergonomics Design

• Design tools to optimize their dimensions relative to a person's anthropometry.
• Women using tools designed for men is an example.
• Size of handle must allow maximum strength
• Reduce exertion of hand/wrist during repetitive activities