Plantaris distal insertion tendonopathy

[Colm McCarthy]

Hi Steve, I have come across a few similar cases in runners – medial calcaneal pain that behaves in a “tendinopathic” type way e,g, warms up with running, sore after. Point tenerness at the medial gastrocs, a little too medial to be achilles insertion. Medial border calc, not plantar surface. Often treated as insertional achilles tendonopathy but I wonder if plantaris insertion is the issue? Small tendon and I don’t assess that often in “normal” cases so I don’t hhave a great mental refernece of what normal looks like. Do you have any images of normal vs tendonopathic? They don’t seem to respond too well to the usual tendon loading rehab. Would you inject? If so, what? Thanks!

[Stephen Bird]

Hi Colm,

Plantaris is an interesting topic.

Take a peek at the medial calf material on the website.

It is covered in a couple of presentations, “A tale of two muscles” and “Medial calf assessment”

At the end of the presentations I talk about plantaris.

My view is that it only very rarely ruptures, and almost never at the medial gastric insertion level and all of the cases I diagnosed in the past are almost certainly tears of the free gastrocnemius aponeurosis (FGA).

My view on this topic has refined over time.

The distal insertion of plantaris can take two patterns. In most people the plantaris blends with the medial fibres of the Achilles tendon and in a smaller minority it stays independent and has its own insertion onto the calcaneum. In some people it is also absent.

With either type it is possible for it to become detached distally, but it is VERY rare and I only see about one per year, while I see dozens of FGA tears each year.

The reason it does not tear is two fold.
Firstly if we were to hold a plantaris tendon at each end I doubt we could break it as it is a tough, flat , long piece of pure collagen.
Secondly the muscle belly is about the size of your index finger, so it is WEAK.
It doesn’t have the grunt to break the tendon.
It is a bit like me walking into a bar and trying to start a fight. I simply don’t have the physical equipment to threaten anybody!!

So a small, weak muscle and a tough tendon = low likelihood of rupture and also the small muscle belly acts as a spring, or shock absorber, further making rupture less likely.

So I would still be betting it is Achilles tendinosis / enthesopathy you are dealing with.

Some people do blame the plantaris tendon for causing medial Achilles tendinosis and I have had several cases where it does look like the area of Achilles tendinosis is immediately adjacent to the plantaris tendon. This does play into the Cook and Purdham song book of tendinosis being due to extrinsic compression of the tendon. So in these cases some do advocate releasing the plantaris tendon.
I am only really convinced of this relationship infrequently.

So if you think the plantaris distal insertion is a contributor to the symptoms it would be easy enough to inject, just on the medial side of the distal Achilles insertion.

Steve.

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