Bones, Muscles, and Ligaments: The Jenga Tower Model of the Lower Leg

Alignment refers to how well the foot and structures on top of the foot, like your legs, stack up on top of each other.  Generally, we want things to be stacked up as close to vertically as possible. Like playing jenga.

(Jenga is that game where you pull blocks out of a tower and stack them on top until it falls over. It suddenly occurs to me that a basic understanding of the game is pretty important to this article, so here: https://en.wikipedia.org/wiki/Jenga)

The foot and leg have a few component parts:

First are bones, the hard bits that provide structure. They are inert and inelastic, like a pile of rocks. If they are stacked on top of each other just right, then they you can make a tower out of them. As a very simplified, but remarkably accurate example: the leg bone sits on top of the ankle bone which sits on top of the heel bone. Now, much like rocks, your bones won’t do anything to hold themselves up. Like a tower of jenga blocks a pile of bones will fall over if you poke it.

Pictured here are the bones in the leg and rearfoot. There are two up top (green), the fibula and the tibia, these are the long bones in your shin. They sit on either side of the talus (blue), the middle bone, to create a hinge joint that lets you do the gas pedal motion. We’ll call the talus your ankle bone, although the knobby bit that sticks out on the outside of your ankle that most folks would point to as the ankle bone is actually part of your fibula. Below the talus is the calcaneus (red), or heel bone, it connects the ankle to the ground. Now unlike the ankle which pivots your foot up and down the heel can tip side to side, but we will talk more about that later.

The bones of the lower leg (green), ankle (blue), and heel (red).

Next are soft tissues, pictured below. To prevent our bones from simply toppling over we have a few other tissues to help hold them in place. These tissues are stretchy and elastic rather than hard and comparatively brittle like bones.

o   Ligaments (green) – these are your elastic bands. They connect bones to other bones. Ligaments are really tough but limited in that they too just sit there. Ligaments won’t hold bones together any tighter than they already were, however, they will prevent them from being pulled apart. A jenga tower held together by ligaments may be pushed over or collapse but all the bones will be held together rather than scattering.

o   Muscles (red) – these are the active component of holding our jenga tower upright, think of them as a rope that someone is pulling on. Muscles are connected to bones by tendons and can pull on the bones to move them around. Muscles can tense up and actually hold bones together more tightly than they would be just sitting stacked on top of each other.

A representation of ligaments (green) and muscles (red) surrounding the ankle.

So the Jenga Tower Model of the Lower Leg has a few strategies with which to hold itself upright:

·       Aligning the bones directly over top of each other so that they can just happily sit there. This requires the least amount of energy but can also be rather hard to maintain. Sure, a jenga tower can sit in one place just fine, but what if it needs to turn around to look behind it, scratch an itch or go for a walk? The tower topples.

·       The ligaments holding the bones together come next. Now the tower might be able to lean or hang over in one direction slightly as the elastic bands around it tighten up and prevent it from actually falling. This too takes little energy as the ligaments are just being passively stretched rather than putting in any active work, but it can cause a lot of wear and tear on the ligaments themselves. Imagine an old elastic band that looks thin and has crinkles in it like a straw bend.

·       Lastly there are the muscles. If the jenga tower really wants to fall over you can throw a rope around it pull on it to hold it up. This takes a lot of effort, and it is putting strain on both the person holding the rope and the rope itself.

One interesting thing to note about ligaments and muscles is that they can only provide tension. They pull on things, they do not- they cannot, in fact, push on things.

Ligaments function passively. They will resist a stretch that is applied to them.

If a tower is leaning to the left, the ligaments that are actually on the left side aren’t going to help it much. They are only going to get scrunched up which will provide minimal support to the leaning tower. It’s those ligaments on the other side that provide the bulk of the support. They get stretched out, but they are like a very stiff elastic band or a tie down cable for a pickup truck, they don’t stretch much. Thus, this tension provided by the ligaments will keep the tower from leaning over too far.

Muscles can actively contract to pull different segments of the ankle tower into a better position.

Muscles also work by applying tension but they do so actively rather than passively. The muscle itself contracts, it does work by shortening its length. This creates a pulling action which is linked to the bones by the tendons. If the tower is leaning to the left a muscle on the left side won’t be able to do much about it, it can only pull the tower closer and it’s already leaning that way we don’t want to pull it closer. A muscle on the right side needs to contract to pull the tower back upright.

Next week we will look at how orthotics can help with the jenga tower.