You may be experiencing the start of a tendinitis. Because we use our feet continuously, tendoinitis in the foot is a common problem. One of the most frequently affected tendons is the posterior tibial tendon (PTT).
The posterior tibial tendon (PTT) runs behind the inside bump on the ankle (the medial malleolus or “ankle bone”), across the instep, and into the bottom of the foot. The tendon is important in supporting the arch of the foot and helps turn the foot inward during walking.
Tendon pathology may begin with an acute injury from a traumatic fall, an ankle fracture or dislocation, or even laceration (cut) of the tendon.
Other factors that seem to put people at risk of PTT deficiency and even rupture include female gender, obesity, diabetes, high blood pressure, taking steroids, or previous trauma or surgery to the mid-foot.
If it doesn’t clear up quickly, call your medical doctor and get an appointment. You may need something as simple as a shoe modification or arch support. Antiinflammatories are often used in the acute phase when there are symptoms such as you describe. Early treatment is advised to avoid having a simple problem progress into something more chronic and resistant to treatment.