For the most part, heel spurs have very little to do with the actual presence of heel pain when heel pain is present on the bottom of the heel. While heel spurs are often found on the bottom of the heel bone, they usually do not have a direct role in the actual case of heel pain.
Heel spurs, whether on the bottom of the heel or the back of the heel, form as a result of traction of some structure, be it a ligament or a tendon, tugging away on the heel bone. In turn, the outer layer of the heel bone starts to develop calcification in the direction of that traction. On the bottom of the heel, pulling of a ligament called the plantar fascia allows for a spur to develop on the undersurface of the heel bone. This spur is parallel with the ground, and does not cause pain when stepped on. What does cause pain is the tugging and eventual damage and inflammation to the plantar fascia itself. The spur is simply a byproduct of this process, and not its cause.