Pain on the inside of the ankle that will not settle: adult acquired flat foot

Some foot problems announce themselves. This one does not. It usually starts as a vague ache along the inside of the ankle and through the arch, the sort of thing you notice at the end of a long day and forget about by the morning. People often live with it for a year or more before asking anybody about it, by which time the shape of the foot has begun to change.

It is known as adult acquired flat foot, and also as posterior tibial tendon dysfunction, which is a more accurate description of what is happening.

What is going on

A tendon called tibialis posterior runs down the inside of the ankle and holds up the arch of your foot. It is doing real work every step, and if the foot is already flat, or flattens more than it should under load, that tendon is working harder than it was designed to.

Over time it becomes inflamed, then degenerates, and can stretch or tear. As it lengthens, it stops supporting the arch, so the arch drops further, so the tendon is loaded more still. That is why the condition is described as progressive. Left alone, it tends to get worse rather than settle, and eventually the change in foot shape can become fixed.

It becomes more likely with age, is more common in women, and is more likely again if you are already flat footed. It also turns up in athletes and in people with inflammatory arthritis.

What it feels like

The pain sits behind and below the inner ankle bone, and often along the instep. It is usually an ache that builds with walking and is worse the further you go or the later in the day it gets. Some people get burning, tingling or stabbing pain as well, where swelling irritates the nerve passing through the inside of the ankle.

Many people also develop heel pain alongside it, because a collapsing arch puts the plantar fascia under more tension.

As it progresses, you may notice the foot looks different. The arch looks lower, and viewed from behind, more toes are visible on the affected side than the other.

The test you can do standing up

Stand near a wall for balance and try to rise onto the toes of the affected foot alone, with the other foot off the ground. A healthy tibialis posterior is what makes that possible.

If you cannot do it on one side, or you can but it is painful, or you can only manage a fraction of the height you get on the other foot, that is a meaningful finding and worth getting looked at. It is not a diagnosis on its own, but it is the single most useful thing you can check yourself.

Treatment

This is a condition where early treatment genuinely changes the outcome, which is the main reason it is worth writing about.

In the early stages, when the problem is inflammation rather than a lengthened tendon, settling it down matters. That means a period away from whatever is aggravating it, along with ice, compression and elevation if it is swollen. On its own, though, that does not address why the tendon was overloaded in the first place.

For most people, supporting the arch is the part that makes the difference. Functional foot orthoses, which are corrective insoles, reduce the work the tendon has to do and are usually needed beyond the initial settling down phase. Supportive footwear, a stiffer boot or trainer, and sometimes an ankle support are prescribed alongside them.

Exercise has a role too, to maintain mobility and to strengthen the tendon itself, but it needs care. Loading a tendon that is already struggling, too hard or too soon, makes things worse rather than better, which is why a programme from a clinician beats a video from the internet here.

A small number of people, usually those who present late or whose deformity has become fixed, need referral for a surgical opinion.

Getting it assessed

Our podiatry team assesses this regularly, including biomechanical assessment of how your foot behaves under load, and we make custom orthotics on site in Haslemere. Where the calf and ankle also need work, musculoskeletal physiotherapy runs alongside.

If you have had an ache on the inside of your ankle for months and have been assuming it will settle, it is worth having somebody look at it while there is still plenty that can be done.