-osis. 1  1 suffix meaning a (specified) action, process, or result: homeosis, narcosis, zygosis. 2  2 suffix meaning increase in a pathological condition: calcicosis, psittacosis, varicosis. -osis. , pl. Combining form meaning a process, condition, or state, usually abnormal or diseased; production of an abnormal substance, increase of a normal substance, or parasitic infestation.
If non-surgical treatment fails to relieve the symptoms of accessory navicular syndrome, surgery may be appropriate. Surgery may involve removing the accessory bone, reshaping the area, and repairing the posterior tibial tendon to improve its function. This extra bone is not needed for normal foot function.
The accessory navicular (os navicularum or os tibiale externum) is an extra bone or piece of cartilage located on the inner side of the foot just above the arch. It is incorporated within the posterior tibial tendon, which attaches in this area. An accessory navicular is congenital (present at birth).