Have you ever heard of the phrase “Turnip thighs?” It's generally used to describe big quads that are heavily developed on the top, but with little development around the knee. This is actually a pretty common sight among many an aspiring bodybuilder, and is most often the result of a poor range of motion - half range squats and half range leg presses.
I often see young guys in the gym with 500 lbs. on a squat bar and 1000 lbs. on a leg press, only to witness them move the weight little more than a few inches. By cutting the weight in half, and using a full range of motion, trainers would see twice the development, and it would be more complete throughout the entirety of the thigh.
Much of the thickness right above the knee is the result of a highly developed vastus medialis, or “tear drop” muscle. Modern day warriors like Jay Cutler, Kai Green, and Ben Pakulski all have exceptional vastus medialis development, and one thing all of these men have in common is that they always squat deep! Usually below parallel.
Ok, so if this is an area of your physique that is lacking, here are some leg exercises that perhaps can kickstart some new growth.