Post-Tib Tendonitis is a strain placed on the posterior tibial tendon. The posterior tibial tendon runs along the inside of the ankle and the foot. When there is post-tibial tendon disfunction, the tendon does not function to hold up the arch, resulting in flat feet. This can lead to heel pain, arch pain, plantar fasciitis and/or heel spurs. With post-tib tendonitis, pain will be more severe upon weight bearing, especially while walking or running.