Articular joints are exquisitly sensitive. If you want to subdue someone physically, usually this is done by compromising one of their joints!

The reason joints are so sensitive is because if the "hinge" is malaligned it degenerates very quickly.

Because joints are so sensitive, small misalignments ("subluxations") cause discomfort or pain.

Before the advent of antibiotics, syphillus in its tertiary stage first attacked the nerves in the spinal cord that carried information about the position of joints. Because of this the joints of people with syphillus often turned to mush - a condition called a "Charcot's joint" (see below).