Arm / hand

Arm/Hand

How the Arm and Hand Work
The arm and hand are designed to perform a range of tasks in many different positions. They are capable of exerting great force as well as fine manual dexterity. Structurally, the arm is best considered in terms of its three major components: shoulder, elbow and hand. Each component has its own characteristics. The shoulder is controlled by muscles in the neck and upper back. The elbow is the least complicated of the components. Together the hand and the wrist have 27 bones. Most of the muscles controlling them are in the forearm.

Ligaments connect the bones to each other and tendons connect muscles to the bones. When a muscle contracts, it pulls the tendon which moves the bone to which it is attached. Portions of these tendons are enclosed in sheaths---shiny and very slippery coverings which protect and lubricate the tendons and permit them to slide back and forth freely. Joints contain bursa, fluid-filled sacks which reduce friction and provide cushioning during motion.

Excessive back and forth movement of a tendon under excess load can cause inflammation (pain, swelling or tenderness) of the tendon or its sheath. Other causes of inflammation in these structures include direct physical trauma, excessive external pressure, and various diseases. When the inflammation involves the tendon primarily, the disorder is known as tendonitis, and when it involves the tendon sheath, it is known as tenosynovitis. When tenosynovitis is associated with the narrowing of the tendon sheath, it can produce trigger finger or de Quervain's disease.

At joints where tendons are unsheathed, such as at the shoulder and elbow, other injuries can occur such as epicondylitis and bursitis with symptoms of pain, tenderness and reduced range of motion. Names you may be familiar with include "pitcher," "golfer" or "tennis" elbow. Pressure on the nerve can produce symptoms of pain, numbness and tingling. These can include problems at the shoulder and carpal tunnel disease, which is compression of the median nerve on the palm side of the wrist.

Regional musculoskeletal illness, cumulative trauma disorder (CTD), and repetitive stress injury (RSI) are terms that have been used to describe repetitive motion problems. Pain can occur from sprains, strains, and acute overuse along with personal medical conditions. Hobbies, participation in sports, activities at home and work tasks can lead to these conditions.

It is important for individuals experiencing persistent pain to have an examination by a qualified medical practitioner to determine the cause of the discomfort, to provide treatment and to help identify activities which may aggravate the condition.

Techniques for Reducing Musculoskeletal Disorders or Discomfort
Musculoskeletal disorders or discomfort associated with prolonged static or awkward posture, or forceful repetitive motions can often be ameliorated by good work practices, training procedures, and workstation setup or tool design.

Work Practices
To reduce the time spent performing one specific motion and to allow time for recovery, several employees on a periodic or rotation basis could perform different tasks. In some instances, it may be possible to design a task so that it can be performed with either hand and the employee trained to alternate hands. All tasks should be designed to minimize stress and strain on the arm from the shoulder to the hand.

Back to top