Usually an arm looks like this:
Shoulder -- upper arm -- elbow -- forearm -- wrist -- hand.
But suppose, because of either chemical poisoning or radiation in utero, Kevin was born without a left forearm. Then his elbow and wrist would be fused into some hybrid structure joint, and the left arm would look like this:
Shoulder -- upper arm -- elbow/wrist -- hand.
Suppose this had already been described in detail. Then Kevin leaves the narrative for a few hundred pages, and when he comes back I want to remind the readers which character he is. In particular I want to remind them of the layout of his left arm because it is to become plot relevant. So I want to insert a marker back to the original description without repeating it.
Since the hundred pages of text only spans a week or so in story (let's make it a working week with the narrator only seeing Kevin on weekends), the narrator certainly doesn't need to be reminded who Kevin is. So I decide to slip in something like. . .
"Kevin cycled at a restrained pace. He knew his _______ arm would prevent him from making quick turns in an emergency."
I think that's a fairly subtle way to remind the readers. But what should go in the blank space? Feel free to muck around with the format as you wish. What I really want is just a summary of the earlier description.