De Quervain’s stenosing tenosynovitis is an inflammatory process affecting the synovial sheath of the thumb tendons (long abductor and short extensor).
The condition is characterized by painful narrowing of the synovium at the point where, these involved tendons pass over a bony protrusion called the styloid of the radius: the increased volume in the digital canal, due to the inflammatory process, creates painful friction during tendon sliding.