Outside ankle pain when you run, and why it is often not the old sprain

You rolled your ankle eighteen months ago. It got better, mostly. There is still something on the outside that shows up towards the end of longer runs, and every physio you have mentioned it to has treated it as a sprain that did not settle.

Sometimes that is what it is. Often it is the two tendons that run behind the bone you are pointing at.

Where they run

The peroneal tendons come down the outside of the lower leg, pass behind the bump on the outside of the ankle, and turn forward along the outside of the foot. They are the main muscles that turn the foot outwards, and they work as stabilisers of the outside of the ankle¹.

The ligaments that get sprained sit somewhere else. They run in front of and below that same bump.

A sprain

Sore in front of and below the ankle bone

The tendons

Sore behind the ankle bone and forward from it

Telling it from a sprain

Most lateral ankle pain after a sprain does settle. The numbers are worth having, because they tell you when lingering symptoms stop being normal.

So pain at three months after a sprain is common and expected. Pain at twelve months puts you in a small minority, and that is the point at which asking whether it is actually the ligament becomes reasonable.

A ligament sprainThe tendons

Where

A ligament sprainIn front of and below the bump.

The tendonsBehind the bump, and forward from it.

How it started

A ligament sprainOne moment, rolling the ankle.

The tendonsGradually, or it never fully cleared after a sprain.

Resisted movement

A ligament sprainTurning the foot outwards is not especially sore.

The tendonsTurning the foot outwards against resistance reproduces it.

Over a run

A ligament sprainOften fine once warm.

The tendonsBuilds through the run and is worse on cambers and trails.

Swelling

A ligament sprainEarly on, around the front of the ankle.

The tendonsOften a fuller, more tube-shaped swelling behind the bone.

Turning the foot outwards against resistance while the ankle is pulled upwards, with a finger over the groove behind the bone, is the examination that separates them¹.

Why a clear scan does not settle it

Runners often arrive having had a scan that showed nothing, which they have been told means nothing is wrong.

The same pattern shows up at the sharp end. Acute peroneal dislocations are misdiagnosed as ankle sprains in up to 40% of cases, even by clinicians who specialise in the foot and ankle⁴.

What makes it more likely

Foot shape matters here more than it does in most running injuries. A high-arched foot with a heel that sits turned inwards puts more demand on the tendons that stabilise the outside, and that shape is a recognised risk factor. A flatter foot changes the picture again, so foot type is part of the examination rather than an afterthought¹.

Laterally posted orthotics and progressive tendon loading are the non-surgical mainstays⁵.

What we do about it

Here is the honest position. Treatment recommendations for peroneal tendon problems come from case series and expert opinion rather than trials¹, and the reviews say the same⁴. There is no equivalent of the heel raise protocols that exist for the Achilles.

That does not leave us with nothing. It leaves us building the plan from what the tendon does rather than from a protocol.

Lateral ankle and foot problems account for a real share of running injuries⁶, and this one is under-recognised mainly because the label sprain arrives first and sticks.

When to get it looked at

The first point is the one to take seriously rather than live with. A tendon that moves out of its groove behind the bone is a specific problem with a specific answer, and it is the one most often mistaken for a sprain⁴.