Musculoskeletal Disorders: Anatomy of an injury
The average person working at a keyboard may perform 50,000–200,000 keystrokes a day. Small, repetitive movements can disturb the delicate balance of muscles, tendons, and ligaments in the hand and cause cumulative-trauma disorders (CTDs), also known as repetitive-strain injuries (RSIs) or musculoskeletal disorder (MSDs). The use of proper keyboard and pointing device techniques, rest breaks, and a properly set-up workstation can significantly reduce the risk of developing an overuse injury.
The nerves that supply the muscles and the skin in the upper extremity leave the spinal cord in a complicated network of nerve fibers, roots and bundles—this is called the brachial plexus. These nerves travel down the side of the front of the neck and divide, then rejoin to form the median, radial and ulnar nerves. These nerves travel down the arm in different paths and provide feeling. The nerve sends the signal to the muscle telling it to contract and allows you to feel sensation where it supplies the skin. If these nerves are compromised in any way, loss of strength and feeling can result.
Nerves can be compromised through repetitive movements. Repeated motions can result in compression or entrapment of nerves. Compression can be caused by tight muscles, inflammation of surrounding tissues, or misalignment of the nerve.
When a nerve is compressed, you feel the sensations somewhere between the point of compression and your fingertips. Ulnar, radial, or median nerve compression can occur anywhere along the path they travel through, from the neck to the hand. Shoulder pain can be referred from a nerve pinched in the neck. Pain in the forearm, wrist, or fingers can originate from compression at the neck or elbow or wrist level. That is why when you have pain in your elbow, wrist or hand, you have to start looking for the cause at the neck and move down the arm.
Nerves can also be compressed in more than one place. This is very common with computer users who have muscle tightness or tension in several places. This phenomenon is called a double-crush injury and can be very difficult to diagnose.
Some common nerve injuries/syndromes that can result from repetitive movements include thoracic-outlet, radial-tunnel, cubital-tunnel, and carpal-tunnel syndromes.
Thoracic-outlet syndrome signs and symptoms include numbness and tingling in the hand, often made worse with overhead activities such as drying your hair with a dryer or cradling the phone between the ear and shoulder. Compression of the nerve often stems from muscle tightness at the side of the neck that can result from poor head position or slumped posture. Sleeping with your hands up over your head or around your pillow can make pain worse at night.
Radial-tunnel syndrome refers to compression or entrapment of the radial nerve at the outside of the elbow. It is frequently caused by repetitive wrist and finger extension or turning of the forearm. Symptoms can occur at the elbow where the nerve is compressed or near the base of thumb, or anywhere in between. Wrist weakness is a common symptom.
Cubital-tunnel syndrome occurs when the ulnar nerve is compressed or entrapped at the inside of the elbow. Common symptoms include numbness or tingling up and down the inside of your arm with tingling into the ring and little fingers. Repetitive bending of the elbow or resting your elbow on a hard surface are common causes of this nerve injury.
Carpal-tunnel syndrome is caused by compression of the median nerve at the wrist. Early signs or symptoms may include numbness or tingling in the thumb, index finger, middle finger, or one half of the ring finger. Persons are often awakened at night by the hand falling asleep. Symptoms are often increased when driving or attempting to hold objects. Frequent dropping of objects is a common complaint.
Tendons are another type of structure that can be affected by repetitive motions. They attach muscle to bone, and are connective tissues that contain little stretch or rebound. If they are stressed beyond their strength by overuse or maintaining a static or prolonged position, they can get tiny tears in them. Friction from overuse can also cause inflammation. This causes a condition known as tendinitis.
Tendinitis occurs most often in the tendons of the fingers, thumb, forearm, elbow or shoulder. Symptoms range from specific achiness, stiffness, tightness, and burning sensations to a deep, non-specific pain. Grasp can be impaired to the point of causing difficulty holding on to objects.
The tendons of the wrist and hand are very small and are at high risk for injury when overused. This can occur with activities such as keying in awkward positions, pressing the keyboard too hard, or holding a mouse or pointing device too tightly or for too long. Although naturally stronger and more durable, the larger tendons in the shoulders can be affected if the arms are held out in front or off to the side, or excessive reaching is done while working. Tennis elbow, or lateral epicondilitis, affects the tendons of the finger extensor muscles at the outside of the elbow. Golfer’s elbow, or medial epicondilitis, affects the tendons of the finger flexor muscles at the inside of the elbow.
Muscles can be strained by overuse, resulting in tiny tears in the muscles. These tiny tears form scar tissue and contribute to inflammation and muscle stiffness. A diffused, achy pain called myofascial pain can result. Painful nodules or tender spots called trigger points can also occur in overused muscles.
Trigger points can occur in almost any muscle. When you press a sore spot, the pain can travel out to a distant area and then recede. This is called a referral pattern. The site of the trigger point is usually distant from the site of the referred pain. Muscles in the neck refer pain to the head, shoulders, upper back and hand. Muscles in the arms can refer pain to the neck, shoulders, elbows, wrists and hands.
Sleep patterns are often disrupted by muscle pain. You wake up feeling stiff and tired even when you think you have had enough sleep. This disruption of sleep and increased discomfort can increase fatigue levels that result from working with overused muscles.
Joints can become stiff and dysfunctional if they are being held in one position for multiple hours day in and day out. The cervical and lumbar spine joints are particularly susceptible to strain when the spine is held in prolonged, awkward postures. Looking down while typing, looking over towards a copy holder off to the side, or sitting slumped in a chair can strain the ligaments in the spine that support the joints and create stiffness and inflammation in a joint.
Avoiding Repetitive-Trauma Disorders
There are several forces that work together to result in a repetitive-trauma disorder. Your work environment, your job, your equipment, and how you use your body are all important components. Increased awareness of your posture and work habits are necessary to enable you to work safely and avoid the problems associated with repetitive-trauma disorders.