Along with pinch blisters, heel edge blisters are the most common blisters we see at ultramarathons. On more than one occasion at the Adelaide 6-Day Ultra 2019, we saw posterior heel edge blisters caused by orthotics. Specifically, orthotics that were ever so slightly out-of-place in the shoe.

posterior heel edge blisters due to an out-of-place orthotic
We saw several posterior heel edge blisters due to an orthotic sitting too far forward in the shoe. 

Orthotic position

A foot orthotic is designed to sit right to the back of the shoe. This way, the heel cup contours seamlessly into the heel counter of the shoe, providing an adequate and seamless space for the heel to sit.

However, it’s not uncommon for an orthotic to slip a little forward – and stay there. Step after step, the bottom of the orthotic makes a little groove into the shoe, and the orthotic nestles into that position by default. The result is, the heel is effectively sitting on the back of the heel cup.

Indent made by orthotic making it sit too far forward
See the indent made by the orthotic. The orthotic will settle into this position by default.

This malposition is often undetected by the wearer, and not a problem when activity levels are low to moderate. But throw 2, 3 or 6 days of continuous running and walking into the equation, and it can soon become blister-causing.

How do you know if your orthotic is in the right place?

Simply feel for a gap between your orthotic and your shoe. It might be as little as 3mm – that’s still significant. Certainly 5mm will give trouble!

Another tell-tale sign is callous at this very location on your heel. Remember, callouses and blisters are caused by the same thing – callous is the chronic result of skin shear, blisters are the acute result.

Orthotic sitting too far forward in the shoe can cause posterior heel edge blisters
This orthotic is sitting about 5mm too far forward in the shoe.

Where do the blisters appear?

In the instance of an orthotic that is sitting too far forward, heel edge blisters will result at the back of the heel edge (rather than the sides). This is where the concentration of pressure is.

As the blister develops, you’ll notice the blister fluid will gather above the point of irritation. Why? Quite simply, it can’t stay where it’s constantly being pushed on. It will follow the path of least resistance and get pushed to a less pressurised and less weightbearing area, ie: upwards.

posterior heel edge blisters caused by orthotic sitting out of place
Posterior heel edge blisters caused by an orthotic which had slipped forward in the shoe

So you must not be fooled into thinking the cause of this blister is higher up. If you concentrate your efforts here, they will be wasted. Hold your orthotic against your foot and you’ll see the area being irritated.

How did we fix it?

It’s not enough to move the orthotic back and assume it will stay there. You have to make it stay there. And the best way to do that is with a piece of double-sided tape under the heel of the orthotic. Place the orthotic appropriately in the shoe, press down HARD, and then put the shoe on carefully. It’s best to undo the laces so you can ensure the correct position is maintained as the foot slides into the shoe. Otherwise, you’ll just reinforce the orthotic in the wrong position.

What else did we do?

By fixing the orthotic into the right position, we’ve taken care of the pressure component of blister causation.

I also like to take care of any friction component to blister causation, especially once a blister has formed, by applying Engo patches using the two-patch technique (demo video:

And finally, I’ll usually attempt to spread shear load by using a rigid sports tape over an area much larger than the irritation itself.

  • For the sake of a long-lasting adhesion, I first apply Fixomull Stretch (sticks really well to the skin).
  • Followed by rigid Elastoplast (does the job of spreading shear load).
  • Followed by another layer of Fixomull (as a fixation for the Elastoplast to ensure edges don’t roll back).

What about other heel edge blisters?

Learn more about medial and lateral heel edge blisters here.

Moral of the posterior heel edge blister story

These are easy blisters to proactively prevent. Make sure your orthotic is sitting in the right place in all of your shoes. If it’s not, head to Bunnings and grab a strong double-sided tape. Problem solved.