Primates, including human beings, are separated from the rest of the animal kingdom by one important digit - the first digit, the thumb. Imagine trying to hold onto a needle, a pen, or a hammer without a thumb; nearly impossible. That is why when the thumb becomes painful and useless a person can lose a job, lose a hobby, and lose the ability to live independently. Three common conditions affect the thumb: arthritis, de Quervain's Tendonitis, and carpal tunnel syndrome. Unfortunately, these three conditions usually go hand-in-hand and attack the same thumb.
In order to understand the thumb, one must know about the most important joint which is at the base of the thumb and called the carpometacarpal joint (CMC joint). The first CMC joint is the only CMC joint that has full range of motion: abduction, adduction, flexion, extension, and rotation. This motion is what gives the thumb full function for grasping, holding, pinching, and squeezing. And out of all the motions of the thumb, the "opposition of the thumb" is the most critical. This ability to draw the thumb across the palm gives primates the ability to hold onto small objects. While the rest of the animal world looks at the thumb with jealousy, primates contend with some thumb problems.
Because the CMC joint is so functional and versatile, it tends to wear out very quickly. Hence, many people develop arthritis of the first CMC joint by the age of 50. This very painful condition can render the hand virtually useless. And not just one hand is affected; usually both sides are affected with the dominant hand being the worst side. Hallmarks of CMC arthritis include tenderness on the anterior (front) portion of the joint and pain with passive extension. Treatment starts by supporting the joint with a splint, keeping the hand warm with an Arthritis Glove, and possibly an injection. Treatment ends with a joint repair surgery. However, CMC arthritis is usually complicated by two other conditions: de Quervain's Tendonitis and Carpal Tunnel Syndrome.
De Quervain's Tendonitis is an inflammatory condition affecting the tendons that operate the thumb, specifically the abductor longus, the extensor pollicis brevis, and the extensor pollicis longus. That's all Latin to most people. To most, all that is known is the constant pain especially with grasping. Usually, well placed injections of steroids can reduce the symptoms of this tendonitis. But treatment is more complicated when CMC arthritis is also involved. A combination of CMC arthritis and de Quervain's tendonitis is enough to render the thumb useless.
Now, add a little Carpal Tunnel Syndrome (CTS) and the whole entire hand can become crippled with pain, numbness and weakness. CTS is a constellation of symptoms caused by compression of the median nerve at the carpal tunnel. The median nerve is one of two nerves that operate the entire hand. Most importantly, the median nerve operates the thumb. The "opposition of the thumb" would not be possible without the median nerve. In severe cases of CTS, all of the muscles at the base of the thumb (the thenar eminence) atrophy in a condition called "thenar wasting." Together, the combination of CMC arthritis, de Quervain's Tendonitis, and CTS is the most debilitating triad for a primate's hand.