Monday, 11 December 2017

So how many bones ARE there in a human foot?

Those of you who participated in our Facebook teaser may wonder why totting up the number of bones in the picture didn't automatically equate to a correct answer (26).

If you open a basic anatomy textbook (or Google the question 'how many bones are there in the human foot' then this is, indeed, the answer you are likely to get:

• Seven tarsal bones (Medial, intermediate and lateral cuneiforms; cuboid, talus, navicular, and calcaneus).
• Five metatarsals
• Fourteen palanges – the big toe only has two, the other toes have three (actually to an embryologist, they all have three: the medial cuneiform starts life as a metatarsal; the navicular, which forms the keystone of the longitudinal arch, as a cuneiform and the metatarsal in actually an elongated proximal phalanx).

Total 26.

However …

This ignores the fact that othopaedists will also include the fibula and tibia which are functionally part of the foot, being connected to it by the medial and lateral collateral ligaments – the ones you sprain when you twist your angle.

So that's 28.

Or the fact that the majority of adults have two additional sesamoid bones underneath their big toe, like miniature kneecaps.

So that's 30.

However …

These bones can commonly be bipartate, that is formed in two parts – so that makes 31 … or 32 – and other bones can also be formed in two parts.

However …

There are also dozens of of other, less common, anatomical variants including up to twenty other sesamoid bones, of which the most common is the os trigonum followed by other sesamoidal toe bones.

However …

You can also have extra bones – particularly toes (Anne Boleyn famously has six toes and fingers – and a supernumerary nipple – which helped fuel the assertion she was a witch). Extra toes can form in several ways, with a variety of extra bones forming.

And finally …

You are actually born with just 22 bones in your foot. Several of the tarsal bones are still just cartilage  at birth that gradually develop into bone as you grow over the first decade or so of life. So children have fewer bones initially; however, some bones have more that one ossification centre, which makes it appear that, at some points in time, they have more than 26 bones … or 30 bones … or (my favourite answer), "lots".

Thanks to all who took part.