Common Types of Cumulative Trauma Disorders (CTDs)

CTDs go by many different names: RSI's (repetitive strain injuries), WRMSD (work-related musculoskeletal disorders), as well as by the specific diagnoses. They are caused by ergonomic risk factors such as force, posture, repetition, vibration, and others. This is a fact sheet describing the main types of CTDs. These can be broken down as disorders that affect muscles, tendons, nerves, blood vessels, bones, or a combination of these.

Muscles

Muscles are the workhorse of the body. They are very strong and flexible tissues that are able to contract and relax. They are what make your bones move. They can be torn and stretched by overuse, with the result of such well-known injuries as strains, "Charley Horses", and cramps. Focal dystonia (writer's cramp) seems to be caused by muscles not responding properly to brain signals. Muscles usually can repair themselves quite easily, particularly in the early stages of injury, since they have an extensive blood supply. So, with rest, most of these injuries get better.

Tendons

Tendons are rope-like tissues that connect the muscles to the bones. Because they concentrate and transmit the force of the muscles, they can easily be torn or stretched.

Over the course of a day some tendons may move backwards and forwards hundreds of feet. You can feel the tendons of the finger flexor muscles moving if you put your finger on the inside of your elbow or on the underside of your wrist when you make a fist. Tendons do not have nearly as much blood flow as the muscles, so they take longer to repair even day-to-day damage. If there is not enough recovery time, they can become swollen and painful. This is what is commonly known as tendonitis. Tendonitis can have different specific names based on the part of the body affected: epicondylitis for elbow tendonitis (including "golfers elbow" and "tennis elbow"), for example.

The muscles that make your hand move are mostly located in your forearm, and long tendons connect them to your fingers. Those that close the fingers into a grip pass through the carpal tunnel in your wrist (more about that later). They have a harder time moving when your wrist is bent, since it makes them bend around a corner. This reduces efficiency of the grip; keeping your wrist straight is preferred, because it transfers more muscle power directly to the grip.

The hand tendons (and others) pass through slippery surrounding tubes called synovial sheaths, that are lubricated with synovial fluid. If these sheaths get irritated and swollen, the condition is called tenosynovitis. The irritation from constant use can also cause over-production of the fluid, leading to swelling known as ganglion cysts or "bible bumps". Sometimes swelling of the tendons or their sheaths interferes with free movement. If left untreated, "Trigger Finger" can result - a condition in which the tendon catches at certain points in its travel, creating difficulty in unclenching a finger.

Nerves

Another class of CTDs results from having nerves crushed or pinched. You have three major nerves running from your spinal cord through your shoulder and down your arm: the median nerve, the ulnar nerve, and radial nerve.

The median nerve runs through the carpal tunnel in the wrist - an opening about the size of a dime. It is surrounded by bones on the top side, and a ligament on the bottom side (at the base of your palm), with tendons also running through the tunnel. If the tendons or their sheaths swell in the wrist, they can put pressure on the median nerve, which can lead to tingling, loss of feeling, and loss of strength in the first three fingers and half of the thumb. This is what is known as Carpal Tunnel Syndrome (CTS), and it can be very debilitating. But be careful in diagnosing CTS; the same symptoms can be caused by the median nerve getting pinched in the elbow, shoulder, and neck. If it is caused in those areas, carpal tunnel surgery (cutting the ligament at the base of the hand, which gives more room for the nerve) will not fix the problem. Proper diagnosis of the condition is very important; usually conservative medical treatment such as anti-inflammatory drugs, rest, and physical therapy, should be tried before surgery is attempted. Most important, if the working conditions that are causing the tendon swelling are not fixed, then it is likely that symptoms will return, even after surgery. Prevention is very important.

The ulnar nerve runs around the underside of your elbow and is what you feel when you hit your "funny bone". The ulnar nerve serves your pinkie and ring finger. The radial nerve serves part of your thumb.

Blood Flow

Blood vessels can be pinched or damaged, as well as nerves. This can lead to numbness, and loss of color and sense of touch in fingers, as well as damage in other locations. A combination of nerve and blood vessel pinching in the shoulder/neck area causes Thoracic Outlet Syndrome-numbness and pain in arms and hands caused particularly by overhead work and poor design of computer stations.

Vibration White Finger (also known as Raynaud's syndrome) is a special case of blood flow constriction and nerve damage in the fingers. It is caused by exposure to vibration, especially in cold temperatures.

Bones

Ergonomic stresses, such as repetition, high force, and impact, can cause swelling of the membranes surrounding joints, loss of the fluid within these membranes, and damage to the "shock absorbers" (cartilage) that form a cushion between bones... Arthritis may be aggravated by the ergonomic stresses that cause some of the CTDs noted above.

Prepared by Nicholas Warren, MS, MAT, ScD and Timothy F. Morse, PhD, ErgoCenter, UConn Health Center, Farmington, CT.

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Common Types of Cumulative Trauma Disorders (CTDs)
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