The ankle appears simple enough, but when a skeletal model allows for more joint movement it allows you to visualize some subtleties in the interaction of the tibia, fibula and talus that are important for squatting/jumping/demi-pointe activities.
The talus is wider at the front than it is at the back, which means that as the ankle dorsiflexes, the tibia and fibula have to expand to make space. Think of a pair of pincers trying to accommodate an expanding balloon (a weird analogy I know...bear with me). The process then has to reverse as the ankle flexes to maintain the stability of the ankle joint.
Because the tibia and fibula meet at two places, movement at the ankle implies a related movement near the knee (at the proximal tib-fib). The specifics of this isn't the easiest thing to visualize, so I won't spend much time describing it. But once the skeleton is put together you can see it with your own eyes and feel it with your own hands. So let's begin.
Step 1: Assemble the Parts
- 1/8'' bungee cord
- 1/32'' bungee
- Dremel tool
Step 2: Join the Tibia and Fibula
Get a sense of how these bones should fit together by holding them together with the talus in place as shown in this picture.
Without doing this, it's going to be difficult to sort out the correct alignment for these two bones. Mark off entry/exit points at both the top and the bottom for the drill holes.
- A narrow path through the head of the fibula and the lateral tibia to hold the proximal tib-fib in place.
- A path through both bones to hold together the distal tib-fib.
- Another path through the malleoli to help hold the talus in place
- A pair of paths that run through the tibia from anterior to posterior between (2) and (3). These will be used to stabilize the ankle in the saggital plane.
Step 3: Join the Talocrual joint
Once you have holes drilled in the medial and lateral malleoli, you'll want to tunnel out an area that can suspend the talus. If you were to just make a single drill hole then the talus wouldn't have the ability to glide within the joint. It would be restricted to the kind of pivoting movements that aren't realistic. Be conservative with this one. In the image below I was a bit aggressive in the height of the tunnel (and how close it was to the superior surface of the talus). This resulted in more play in the joint than I would've like.
Step 4: Stabilize the foot in the sagittal plane
With no additional stability, there will be a tendency for the ankle to wobble a bit much. To stabilize it, drill through the navicular and the calcaneous as pictured, then attach the cords at the distal tibia (#4 holes above). Adjust the tension so that the foot is held in a neutral alignment just by the passive tension of the bungees.
In a future iteration, I plan to drill through the talus instead for the navicular, because I think it would be less disruptive to the midfoot. Live and learn...
The Finished Product
Here's a video walking through of the completed model and a photo of the sort of thing you're likely to see on most skeletal models. Big improvement!
Anatomical sketches by Henry Vandyke Carter via Wikimedia Commons