Abstract: A system, method, and tools including a subtalar arthroereisis implant for use in reducing calcaneal eversion, blocking anterior and inferior displacement of the talus, and blocking excessive pronation and the resulting sequelae, while allowing normal subtalar joint motion. The method includes in the preferred system inserting a probe to slightly dilate the tarsal canal, inserting a cannulated “sizer” having a guide element placed therein into the dilated sinus tarsi resulting in the guide element being inserted through the tarsal canal. The sizer is removed, leaving the guide element in place. Once the implant has been sized, a trial implant in inserted by placing a conically shaped “nose cone” on the guide element ahead of the implant. Once the trial implant is in place, sizing is checked, the trial implant is removed, and the actual implant is inserted following generally the same procedure as for the trial implant.