Upper limb exoskeletons are engineering controls that can reduce musculoskeletal disorders (MSDs) of shoulders and arms by relocating the burden of hand tools on a worker’s body in overhead tasks.
Hazard Analysis — Overhead work
Workers who perform manual demolition may face hazards from overhead work.
Applying coats of plaster or stucco can lead to shoulder tendonitis and non-specific shoulder pain. Tendonitis occurs when the tendon becomes inflamed. Tension neck syndrome (myofascial pain syndrome) is characterized by pain in the shoulder-neck region along with tenderness over the shoulder-neck muscles. It is one of the most common work-related MSDs of the neck and shoulder.
Overhead work is a risk factor for musculoskeletal disorders (MSDs) such as tendonitis of the shoulder, and lifting can cause MSDs of the back and shoulders. The worker may also experience neck pain or injury, because the neck is frequently in an extreme position during overhead work to allow the worker to see what s/he is doing.
Work-Related Risk Factors
- Working with the hands above the shoulder level ("overhead work")
- Repetitive lifting of the shoulder especially out to the side
- Frequent static contractions of the shoulder
- Use of hand tools during overhead work
Engaging in sports in which the arms are frequently overhead or rotated (such as swimming and throwing a softball) may contribute to the development of shoulder tendonitis. Age is also a risk factor for shoulder tendonitis.
Workers with shoulder tendonitis often experience pain when the shoulder is lifted and rotated. The area where the tendons attach to the bone of the upper arm (humeral head) may feel tender. In addition, workers may experience a limited active range of motion in the shoulder. Pain may radiate into the upper arm.
Development and Progression
Tendon degeneration results from mechanical stress and reduced blood flow to the tendon. The blood flow to the tendon can be reduced because of impingement and muscle tension.
Shoulder tendonitis has been categorized into three stages. Stage I is characterized by swelling (edema) and bleeding (hemorrhage). This stage is most commonly seen in individuals under the age of 25 who have histories of overhead work or overhead activity in sports. In Stage II, there is further deterioration of the tendon and bursa. Individuals with this stage of tendonitis are typically 25 to 40 years old. In Stage III, there may be bone spurs and partial or complete tendon rupture. This stage is usually seen in individuals over the age of 40.
The shoulder bursa is a fluid-filled sac that reduces the friction in the shoulder joint. Repetitive work involving the shoulder may cause the bursa to swell and become inflamed. This condition is called bursitis. Bursitis and rotator cuff tendonitis often occur together.
Common Treatment for Shoulder Tendonitis
Without rotator cuff tear:
For shoulder tendonitis without a rotator cuff tear, it is generally best to attempt conservative (non-surgical) treatment first. This includes rest and avoidance of overhead activities. Stretching exercises and physical therapy are often beneficial. A doctor may prescribe oral non-steroidal anti-inflammatory drugs (NSAIDs), or administer a cortisone injection into the shoulder. Many patients experience a gradual improvement in pain and function over several weeks or months.
If conservative treatment fails to relieve pain, surgery may be considered. Surgery is performed to create more space for the rotator cuff by removing the impingement. The most common surgical treatment is called subacromial decompression or anterior acromioplasty. Patients may continue to experience pain for 2-4 months after surgery.
With rotator cuff tear:
Conservative treatment for a rotator cuff tear is similar to that for shoulder tendonitis. Rest and limited overhead activity are advised, and a patient may also be told to wear a sling to support the injured arm. Anti-inflammatory drugs and a cortisone injection may be used. Strengthening activities and physical therapy are also helpful.
Should surgical treatment become necessary, a surgeon will typically perform a debridement, which is a trimming and smoothing procedure that eliminates the impingement on the rotator cuff. If there is a complete tear, the two sides of the tendon may be sutured together. After surgery, the arm initially will be immobilized. Following this, the patient will begin an exercise program. The patient may not experience complete recovery for several months.
Low Back Pain (LBP)
Low back pain (LBP) is among the most common health complaints in working-aged populations worldwide. In the U.S., 70%-80% of adults will experience a significant episode of LBP at least once in their lives. Low back disorders are conditions associated with lifting and other forceful movements of the back. Episodes of LBP are characterized by varying levels of pain and symptoms in the low back (lumbar spine). Low back problems can even cause leg pain at times.
Work-Related Risk Factors
- Work-related lifting and forceful movements
- Whole body vibration
- Awkward postures (bending and twisting)
- Heavy physical work
- Psychosocial factors such as poor job satisfaction, perception of intensified workload, lack of job control, and certain personality traits
- Lifestyle factors associated with LBP include smoking, a sedentary lifestyle, and obesity.
Development and Progression
The low back may be injured due to either an acute traumatic event or the cumulative effect of stressful activities. Strains of the muscle or sprains of the ligaments surrounding the spinal joints occur most commonly. Injuries to the low back may also involve the intervertebral disc.
The intervertebral disc is composed of a ring of fibers surrounding a sac of fluid or gel-like material. The structure of the disc may be damaged due to acute trauma (e.g. a fall, slip, or catching an unexpected load), or cumulative problems could develop when stressful activities stretch, tear, or unravel the protective fibers surrounding the sac of fluid. When the fibers can no longer contain the fluid, small leaks or bulges can occur or the disc may flatten. In the case of low back disorders, the intervertebral discs are stressed mostly in the weak area of the back between the 4th and 5th lumbar vertebrae (L4-L5), or between the 5th lumbar vertebrae and the sacrum (L5-S1). Disc problems may lead to a pinched nerve.
The causes of many episodes of LBP are unclear. Even with clinical tests and imaging procedures, about 85% of patients cannot be given a precise diagnosis. The pain in these cases is presumed to be related to soft tissue injury or degenerative changes.
Individuals with low back problems typically experience pain in the low back (lumbar spine). Leg pain may accompany low back pain. Most often leg pain is localized to the side or back of the thigh, but sometimes the pain may go all the way to the foot. This leg pain is commonly called sciatica. Individuals may also have tenderness in the low back and a limited range of motion for bending forward, backward, sideways, or twisting. Bending forward tends to increase pain levels.
Initial treatment for most episodes of low back pain may include one to two days of bed rest or avoidance of stressful activities. Nonsteroidal anti-inflammatory drugs (NSAIDs, e.g. ibuprofen or naproxen) are often helpful, and stronger drugs may be prescribed (muscle relaxants or narcotics) for more severe, acute pain.
Other treatment options may include application of heat and cold, physical therapy, spinal manipulation, or injections. Some LBP cases may require surgery (ruptured disc, severe trauma cases, or cauda equina syndrome).
Prognosis for occupational LBP is good. Half of workers improve in one week and 90% improve in 30 days, regardless of treatment. Light duty work activities may be prescribed by the physician during the recovery period. The remaining 10% of workers may have a chronic condition and may not be able to return to their previous jobs.
Tension neck syndrome
Tension neck syndrome (myofascial pain syndrome) is characterized by pain in the shoulder-neck region along with tenderness over the shoulder-neck muscles. It is one of the most common work-related MSDs of the neck and shoulder. Occupational groups with work tasks requiring repetitive arm movements and constrained work postures show high rates of tension neck syndrome.
Work-Related Risk Factors
- Static contractions of the shoulder-neck muscles (when the muscle contracts but there is no movement, such as the muscle activity used to hold the head in a twisted position)
- Repetitive movements of the hands and wrists.
- Constrained head and arm posture (when a task requires a worker to remain in a certain position for a prolonged period of time)
- Holding the head in a bent/twisted position
Symptoms of tension-neck syndrome include activity-related pain, stiffness, and severe pain when in extreme positions (e.g. with the arm fully extended). It is difficult to diagnose this disorder using objective tests, because blood tests and radiographic examination are typically normal. However, it is important that workers undergo a thorough examination in order to exclude other diagnoses related to the neck and shoulder.
Development and Progression
One possible explanation for tension neck syndrome is that muscle fibers become overloaded when the shoulder muscles are statically contracted for long periods of time. This causes muscle pain. In cases of chronic neck pain, it is possible that an initial injury does not heal completely. Pain receptors (nociceptors) in the neck area may become more sensitive to stimuli. When these nociceptors send messages to the brain, the brain may perceive normal activity as being painful.
The prognosis for tension-neck syndrome varies among individuals. In general, pain and discomfort may be decreased but not eliminated. It is important to begin rehabilitation early to minimize the amount of time lost and the level of the disability.
Workers who have been diagnosed with tension-neck syndrome may require ergonomic modifications of their workstation and job redesign. It can also be helpful for workers to be trained to minimize strain during work by avoiding static contractions that last for a long time. Strengthening and stretching exercises can reduce pain and increase performance, though workers may experience a temporary increase in pain at the beginning of the training. Psychosocial factors at work and at home can make treatment of tension-neck syndrome more difficult and less effective.
To assess exposure to overhead work determine how many hours per day the worker spends with their shoulders elevated >60°.
To assess the exposure to overhead work, it is necessary to observe a worker applying coats of plaster or stucco. Look for:
- time spent with the shoulders elevated above 60°
- weight of loads lifted and lifting position
- time spent with the neck in an extreme and/or sustained posture.
Finally, consider the time the worker spends each day performing this task.If this task is only a small part of the worker's day, the extreme postures that are assumed may not be overly harmful.The NIOSH lifting guide aids in the evaluation of jobs involving lifting and the design of safe lifting tasks (NIOSH, 1994).
There is no easy way to measure the actual load on the lumbar spine in the workplace or to correlate measured load with risk of back pain. For a job activities assessment, one should, as much as possible, quantify the worker's exposure to factors found to be associated with increased risk of back pain.
Thomas Bernard's website has a host of practical ergonomics tools, including the Rodgers Muscle Fatigue Assessment, the Moore-Garg Strain Index, and the Rapid Upper Limb Assessment (RULA) Index, which can be useful for assessing overhead work.The Utah Back Compressive Force method can be used to estimate the load on the lumbar spine during lifting.
Thomas Bernard's website has a host of practical ergonomics tools.
WISHA Checklist for Work-Related Musculoskeletal Disorders.
http://www.lni.wa.gov/wisha/ergo/evaltools/HazardZoneChecklist.PDF (Hazard Zone)
http://www.lni.wa.gov/wisha/ergo/evaltools/CautionZones2.pdf (Caution Zone)
Regulations & Standards:
There is no Federal OSHA standard specifically for this hazard. However, hazardous work activities or exposures that are not covered by a specific standard are covered by the general duty clause, which requires each employer to provide a safe and healthful workplace.
Regulations adopted by a state must be at least as protective as the corresponding federal standard. Work may also be subject to rules of other federal, state and local agencies. Even where there is no hazard specific standard, OSHA provides a general duty for the employer to provide a work site free from recognized hazards.
The American National Standards Institute (ANSI) has a standard which applies to construction work where there may be risk factors for musculoskeletal disorders. ANSI standard A10.40 is not a regulation, but implementing this standard can help reduce the risk of MSDs. The standard is available for purchase from the American Society of Safety Engineers: http://www.asse.org/departments/standards/.
Federal OSHA Standards are enforced by the U.S. Department of Labor in 26 states. There are currently 22 states and jurisdictions operating complete State plans (covering both the private sector and state and local government employees) and 5 - Connecticut, Illinois, New Jersey, New York and the Virgin Islands - which cover public employees only. If you are working in one of those states or jurisdictions you should ensure that you are complying with their requirements.
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