I don't recall this many quad injuries - maybe Kawhi's injury has shed more light on it.

Here is a brief tutorial on the quad:https://www.cbssports.com/nba/news/m...-next-for-him/

Are there aspects of a quad tendon injury that make it a tricky one to rehab?

Stotts: Yeah, because it's an extremely powerful muscle. People have to remember the quadriceps is a muscle group -- it's four muscles, that's where it gets its name from. People tend to forget how much we use our quad, and how important it is to our knee -- for stability, for the ligaments inside, for so much of what we do just on a day-to-day basis involves the quad.