Your kneecap is a sesamoid bone. There are a couple more under your big toe joint, the joint that turns into a bunion if you aren’t lucky; sesamoids are kind of like the block to your tendon’s tackle, reinforcers that help modulate heavy or sustained loads. The ones I have mentioned come standard with the model but actually they can arise anywhere and if you punish your body enough here or there, you will get them. Massage therapists come to expect them, unless we are exclusively doing the kind of ethereal energy work that I am way too crude and ruthless to tune into.
They pop up in my extensor tendons now and then. Sometimes they resorb, possibly because I change my work habits. Today I noticed I had grown a beaut in the tendon of my left ring finger, big enough that it feels a tiny bit bizarre when I flex at the metacarpophalangeal joint, like a friendship bead is tunnelling under the skin of my hand.
I think I should name it. Suggestions?