De Quervain’s tenosynovitis
Pain in the side of your wrist near your thumb is most commonly caused by thickening of the tendons and painful nodules at the back of your thumb at its base, particularly where the tendon is held in place by a tough fibrous sheath called the extensor retinaculum. Over time this can lead to basal thumb arthritis.
Such thickening prevents your tendons from freely gliding through your extensor retinaculum leading to pain and swelling, a condition called De Quervain’s tenosynovitis. It most often affects mothers of young infants as a result of straightening the thumb for extensive periods of time when carrying and feeding their baby.
A good test for De Quervain’s tenosynovitis is the Finklestein test. Bring your thumb across your palm and enclose it by making a fist. Then side bend your wrist away from your thumb. If you experience pain at the outside of your wrist then you are probably suffering from De Quervain’s tenosynovitis.