There is normally 26 bones in each foot of most people. However, in some people there can be one or more accessory or extra bones. In most cases these are not relevant and will never cause a problem. In a few cases they can become painful and need treatment. One of these in particular is called an accessory navicular. This is an extra piece of bone that develops on the inside of the arch area of the foot next to the navicular bone. It is seen as a lump of bone that juts out at the highest point of the arch on the inside of the foot. Generally these are not a problem, but sometimes problems do develop. The problem can come from pressure on the enlarged piece of bone from the shoes. Symptoms can also develop as the extra bit of bone changes the angle of pull of tendons that are attached to it, meaning that the muscles cannot support the arch of the foot like they should.
A particular problem that can develop with this condition occurs in ice skaters. Ice skates are quite firm and need to be very firmly attached to the foot. This means that a lot of pressure is placed on the accessory bone on the navicular by the ice skates, then combine that with all the different motions that the foot tries to go through during skating in those tight fitting skates, then the pressure is exaggerated. Initially the treatment for this is to use padding in the shape of a donut to get pressure off the enlarged bone to give some pain relief. Sometime the footwear, or as in the case of ice skates, they can be heat moulded to accommodate the painful area. If this is not successful, then a surgical removal of the extra piece of bone is indicated. If you think you have a problem with an accessory navicular, then see a good podiatrists.