Feet can tell stories
Our footprints tell our story to those who can read them. Which direction we were walking in, if we were going slowly or fast, and much else. The feet are also the intermediaries between us and the ground. Sometimes they need to be soft and receptive and other times hard and rigid. They tell us what we are standing on. If it is rough or smooth, hard or soft, slippery or dry.
In the following I will describe the basic anatomy of the feet. Each foot has 26 bones, 31 joints and 20 intrinsic muscles. But don’t run away – this is a brief tour. Later articles will explore the bio-mechanics of the foot and how all of this knowledge can be used in yoga asana practice. Like the Rubik’s cube, the foot changes as we move. It is not a simple structure. It can be difficult to figure out in its complexity.
The ankle joint
The ankle joint is actually 3 joints: the tibiofibular, talocrural and subtalar joints.
I will describe this ingenious design in order, from the shin down towards the toes. If you can, kick off your shoes and feel these bones and joints with your fingers as you read.
Bones of the feet and ankles (image from: visual dictionary and subject to their license)
The tibiofibular joint
The tibiofibular joint is a fibrous joint between the two lower leg bones. The main ligament forming this joint is called the crural tibiofibular interosseous ligament. Its purpose is to strap the tibia (the shin bone) and fibula (the outside of the lower leg) closely together and act as one while still allowing a slight twisting movement.
The talocrural joint – the hinge
What is commonly known as the ‘ankle bones’ are: the end of the tibia on the inside ankle (medial malleolus) and the end of the fibula on the outside of the ankle (lateral malleolus). Together, these ends form a channel about 30mm wide which fits over the talus bone. This is the talocrural joint. Where leg meets foot.
This channel is referred to as a mortise; a carpentry term. It is the main hinge of the ankle; it pivots forward but has a little bit of slide as well.
The crural tibiofibular interosseous ligament between the lower leg bones (see above) is responsible for preventing the mortise from splitting open; that is, the tibia and fibula separating from each other.
The subtalar joint – the second hinge!
The subtalar joint is on the underside (inferior side) of the talus, between the talus and the heel bone (calcaneus). This is another hinge joint directly underneath the talus. Its angle is offset outward at around 45 degrees. It helps to give the foot a lot more movement options.
Pushing the foot away from the shin (plantarflexion) and pulling the foot towards the shin (dorsiflexion) mostly occur at the first hinge (the talocrural joint). Turning the foot in and out (supination and pronation) mostly happens at the lower hinge (the subtalar joint).
Now, let’s carry on down into the mid-foot.
The stone arch
The calcaneus and talus (which we have described above) along with the navicular, cuboid and three cuneiform bones are collectively referred to as the tarsal bones.
I love feeling these with a skeleton model because I think they are remarkable. They fit together like a 3D jigsaw puzzle. The tarsals are like little mini cubes of a Rubik’s cube. Our tarsals can’t quite swivel around like a Rubik’s cube but they jostle together with a fair bit of freedom, which is how we can manage to slide our feet into a pair of boots. This is really the wonder of the human foot. It can be pliable one moment and solid the next.
Schematic of the bones of the feet (image from Wikimedia licensed under Creative Commons GFDL)
When these tarsals fit firmly together they form a sturdy little stone arch, which we normally call the instep. In its ‘blocked’ together form, the instep is solid enough to strike a football and propel it at speeds of over 150 km/h. I think that is amazing.
In front of (anterior to) the talus and calcaneus sit the navicular and cuboid bones. The navicular is on the inside (medial side) and the cuboid is on the outside (lateral side). The navicular and cuboid bone together, and the talus and calcaneus together, form the transverse-tarsal arch, also referred to as the mid-tarsal arch or Chopart’s joint. Inversion and eversion happen at this joint. A chronically flat foot is one where the navicular has collapsed toward the floor.
Anterior to the navicular and the mid-tarsal joint are the three cuneiform bones. Like three little cubes that fit together, they are why the inner arch is higher and longer than the outer arch.
Anterior to the three cuneiform bones are the first three long metatarsals. They reach out to the first three toes. This medial side of the foot is built for propulsion; pushing the ground away as we walk or run. The first metatarsal is much thicker than the others as it is the base for the big toe. The 4th and 5th metatarsals on the outside (lateral foot) attach directly to the cuboid bone. This side of the foot is built for receiving and transferring the force to the ground as we step and supporting our weight as we stand.
The first 3 metatarsals, cuneiform, navicular, talus and calcaneus all form the medial arch of the foot. The lateral arch is formed by the 4th and 5th metatarsals, the cuboid and calcaneus. The transverse arch is formed by the cuneiform and cuboid bones together with the proximal ends of the metatarsals. Together the three arches form a kind of dome under the foot.
And finally the toes
The phalanges, aka toes, are the little bones attached to the tarsals. Between the tarsals and phalanges are the first knuckles, called the metatarsophalangeal joints… which is quite a mouthful.
The evolution of the human bipedal, upright gait has allowed our species to walk to every corner of the planet. Like every other part of our body, the feet have adapted perfectly to this rather strange but successful habit of being on two legs. In the next post we will unpack the function and the actions of the foot and make it relevant to yoga asana.