Believe it or not the human body is not designed to play video games efficiently. The biggest impact ergonomics has in video gaming is often finding a control scheme that is efficient for the body. This often revolves around a controller for your hand or hands. The most popular style of controller is a two handed controller with the thumbs doing most of the work. And that is what leads to Gamer's Thumb.
Gamer's Thumb is a repetitive stress injury that affects the thumb and wrist. Pain and sometimes a popping sound are present on the outside of the thumb at or near the wrist. There can also be a decrease in grip strength or range of motion.
You see, the thumb is very good at pulling inwards towards the wrist. The muscles and mechanics of your anatomy supports this function. This provides grip, what the thumb is really for and what separates us from most animals. The thumb is more like a jaw and less like a prehensile tail. In other words it excels at clamping down on stuff but isn't really made to be a dexterous appendage performing lots of three-dimensional motions. That puts a lot of repetitive stress on the thumb joint and the muscles and tendons attached to it.
Gamer's Thumb can be a form of tendonitis, tenosynovitis or a combination of both of those disorders. In either case it means something is irritated, inflamed and swollen. In Gamer's Thumb there is an inflammation in the tendons and/or the synovial sheaths that cover the tendons that control the motion of your thumb. It may also be an inflammation in the tenosynium, a slippery membrane that acts as a sliding surface, in the opening in the wrist that the tendons slide through. Often the swelling from the inflammation in either the tendon or tenosynovitis causes irritation that leads to inflammation in the other after repetitive use. It can be quite painful and reduce your ability to grip.
Whichever part of the anatomy is irritated and inflamed it squeezes the tendons and constricts their ability to slide within the sheath. The inflammation results in swelling and pain that can run from the tip of the thumb all the way down to the wrist and even the upper portion of the forearm.
In Gamer's Thumb you often feel the pain when you turn or flex your wrist or when you make a fist or grab something. It often occurs in gamers who play daily for long periods and is even more prevalent in gamers who do not stay physically active.
If left untreated Gamer's Thumb can worsen and the repetitive inflammation and irritation of the tendon's synovial sheaths causes them to thicken and degenerate. This can result in permanent damage leading to a loss of grip strength and/or range of motion as well as constant pain and probably the end of your gaming experience.
Gamer's Thumb is technically known as De Quervain's syndrome. There are many aliases for De Quervain's syndrome with one in homage to the inventor of the current hand controller scheme, Nintendo Thumb. De Quervain's Syndrome can be treated at home effectively if it has not gotten that severe. If you are a serious gamer you should consider trying to prevent De Quervain's syndrome to keep your hand healthy and your top scores high.
The Technical Explanation
If you flatten your hand out with the back of your hand downward then your thumb can move in two ways. It can move up and back down. This moves your thumb out of the plane of your hand and is called palmar abduction. Your thumb can also move left to right staying within the plane of your hand. This type of movement is called radial abduction.
These tendons are housed within synovial sheaths through the wrist passage. Synovial sheaths are kind of like a stiffer, outer tube that can bend but does not kink. The result is that when the wrist is bent or twisted the tendons can still slide back and forth through the wrist passage without getting snagged.
The tendons pass through an opening in the wrist on the thumb side. This opening is covered in a slippery membrane called tenosynovium. Constant friction against this surface by inflamed synovial sheaths can cause inflammation in the tenosynium as well. Inflammation of a tensynovium is called tenosynivitis.
The tendons involved in Gamer's Thumb are those attached to the extensor pollicis brevis and abductor pollicis longus muscles, or the muscles that move your thumb in radial abduction. The muscles run side by side on the back of your forearm towards your wrist and the tendons run along the thumb from the tip to your wrist through an opening in your wrist where they then attach to the muscles.
In Gamer's Thumb, irritation from repetitive stress causes the inflammation in the tendon or synovial sheath which leads to swelling and enlarges a portion of the tendon making it difficult for the tendon to pass through the opening in the wrist. Or it causes inflammation in the tensynovium which results in the same thing. Often, when one is swollen it causes the other to become irritated and inflamed as well, thereby compounding the problem.