Perhaps in my attempt to boost mileage and do speedwork/tempos at the same time, I came down with a knee injury and a foot injury last week that I self-diagnosed as "Seseamoids" (definition of that below, from Running Times). Anyway, knock on wood, all seems ok now.
"Two small bones under the ball (head) of the first metatarsal are known as the sesamoids. These bones are in the flexor tendon to the big toe and act as fulcrums for flexing the toe; they are weight bearing structures. Runners may experience several sesamoid problems.
Inflammation of one or both sesamoids is known as sesamoiditis; increasing mileage, doing speed work and hill repeats, and poor footwear may all contribute to this problem. The affected sesamoid will be very tender to touch and pain may occur when the big toe is flexed upward. Swelling may be present under the first joint. Treatment includes application of ice to the area, anti-inflammatory medications and protective padding (dancer’s pad) that is cut out at the tender area, eliminating pressure on the sesamoids. If this relieves pain, easy running may continue. Sesamoiditis usually resolves in two to four weeks. If there is pain with pushing off, cross training should be performed to avoid an abnormal gait and the myriad of injuries that it may cause. On occasion, immobilization may be necessary to eliminate sesamoiditis.
Sesamoid pain may be due to a stress fracture of one of the bones. A bone scan is often needed to diagnose this injury. It is not uncommon for one of the sesamoids to naturally be in two pieces (bipartite); this does not cause pain, but may create a diagnostic challenge if a sesamoid fracture is suspected. Treatment is similar to sesamoiditis, though impact activities should be minimized. The sesamoids have a poor blood supply, so stress fractures may take several months or longer to heal. On occasion, there is persistent pain; as a last resort, the affected sesamoid may be surgically excised."