So you have sharp pain at the ball of the foot behind the large toe? Has there been an injury? No? Does it hurt or grind with movement of the joint? No? Does it hurt with pressure on the bottom of the foot behind the large joint? Yes? Have you changed to new shoes, changed your ambulating surface or style of ambulating? Have you increased your ambulation, stepped on a rock, twisted your foot?
You may have sesamoiditis (inflammation of the sesamoid bones) or a fracture of one of the sesamoid bones. These are the normal bones under the first metatarsal head. They function as a "pulley" system for the tendon apparatus that flexes the large toe downward. They also protect the long flexor tendon. They help to stabilize the large toe when the heel lifts off the ground.
Protecting the sesamoids with padding, custom arch supports, a stiff-soled shoe or a wooden soled surgical shoe are some measures to help deteriorate pain. Ultrasound and soaks are adjuvant therapy. Anti-inflammatory medications or a localized steroid injection are useful also. Rarely does a cast need to be applied. Occasionally a non-healing fractured sesamoid must be surgically removed.