How did I not know about this? After a good solid decade of reading regularly and widely about knee pain, I am flabbergasted that I had never heard of the fabella.
How many people have this osseous oddity? Apparently it’s not clear. Driessen et al: “The presence of the fabella in humans varies widely and is reported in the literature to range from 20% to 87%.” That’s quite a range!
It may form for the same reason the patella is there (leverage, high stresses), and it can get to hurting just like the patella (fabella syndome).
Filed under “well I be danged”! And I’ve added it to the patellofemoral syndrome tutorial, of course — mainly for the novelty of it, since fabella syndrome isn’t likely to be confused with kneecap pain.