Repetitive stress injuries are common occurrences affecting various body parts. The thumb is particularly susceptible since the fingers are used for almost every daily task. The thumb is designed to perform complex mechanical motions, but when such motions are repeated rapidly and for a long time or repeated slowly but with more force, repetitive stress injury can result.
Definition
The term repetitive stress injury is often used for symptoms where there is no exact corresponding pathology. It is also common to use it as an umbrella term to describe a wide range of activity related pains such as carpal tunnel syndrome, golfer's elbow and trigger finger to name a few. However, in the thumb, there are specifically named conditions resulting from repetitive stress and that are frequently diagnosed today. One of the most common is deQuervain's tenosynovitis.
Repetitive Stress Pathology
The precise reason why repetitive stress injuries occur is not completely understood. However, with repetitive stress injuries resulting in tenosynovitis, it is known that the sheath surrounding the tendon becomes inflamed. This inflammation can result in debilitating pain. It results from diminished space between the tendon and its sheath. As a result, instead of gliding smoothly, the tendon rubs on the sheath, irritating nerve endings and causing pain. The reason why the sheath inflames in some people but not others is unknown.
Mechanisms of Injury
Although still debatable, it is observed that certain thumb movements are associated with the incidence of repetitive stress injury. The International Journal of Experimental Pathology reports that such injuries can occur if the thumb is repeatedly moved in any of its many possible directions, although apposition and reposition are the motions most responsible for injury. Text messaging is a good example of this kind repetitive stress on the thumb. Additionally, if the thumb is moved for shorter periods of time but with far more force, it also can be injured. An example of this is weightlifting.
DeQuervain's Tenosynovitis
While scientific reports are controversial, deQuervain's tenosynovitis is still considered one of the most common repetitive stress injuries of the thumb. Also known as washerwoman's sprain, deQuervain's tenosynovitis involves inflammation of the tendons at the base of the thumb. These are the extensor pollicis brevis and the abductor pollicis longus tendons. The condition produces symptoms of pain, tenderness and swelling over the thumb portion of the wrist, with particular difficulty in gripping. It can be treated with rest, exercise and, in some instances, cortisone injections or surgery.
Other Injuries
There are several other named repetitive stress injuries involving the thumb. According to the American Society of Safety Engineers, the condition becoming most commonly diagnosed is known as "Blackberry thumb". This occurs specifically with extensive text message and may be a subset condition of deQuervain's tenosynovitis specifically caused by texting. Its symptoms are identical, and it is treated similarly to deQuervain's tenosynovitis. Lesser known conditions such as gamekeeper's thumb, skier's thumb and trigger thumb are injuries of the thumb caused by repetitive stress. They are thought to arise from prolonged grasping or clenching and unclenching the hand.
References
- "Intrernational Journal of Experimental Pathology"; The mechanobiological aetiopathogenesis of tendinopathy; S. Arnoczky, et. al.: August 2007
- EOrthopod: de Quervain's Tenosynovitis
- CCOH: DeQuervain's Disease
- American Society of Safety Engineers: Ergonomics
