An accessory navicular bone can alter the force vector for the posterior tibialis, making foot inversion more difficult and potentially requiring orthotics or strengthening of the posterior tibialis.

“I'm sure you've seen people that have an accessory navicular so it's almost an extra bone that sticks off that navicular and you can see it when you're um looking at someone it looks like they have a protrusion um because the posterior tib has to come down and wrap around the navicular if you have an extra bone there the vector of force right is longer so the way I'll describe this to my patients is if you were doing a chest press for example and you starting here imagine having to start all the way back here right it'd be more difficult y so that's where with those patients when you see that or you see that they have an arch that doesn't want to you know recoil or function you have to consider hey we really need to go after after strengthening postor tibialis for example”