Why are talar neck fractures so prone to avascular necrosis?
Sometimes a simple x-ray can say it all. With all of the advanced testing that we have today, a simple x-ray can speak volumes. You aren’t always able to capture the subtleties of bones and joints with each and every x-ray. But every so often, you see a film that speaks to you.
The lateral foot x-ray in this post shows what is called the nutrient artery of the talus. That small bullet shaped hole is the primary in-flow point for blood flow to the talus. Why is that important? Talar fractures typically happen through what is called the neck of the talus (the black line). And that’s exactly where this image shows the nutrient artery.
Most bones have a redundant blood supply so that when a fracture occurs at one end of the bone, the opposite end of the bone is called into action to participate in healing. But the talus is different. Although it has a small amount of redundancy, such as arteries coming in from both the medial and lateral sides of the talar neck, the fault in that redundancy is that the in-flow into the talus is all within the neck of the talus. Unfortunately, the neck of the talus is where the majority of fractures take place. Therefore, even simple talar neck fractures are prone to loss of blood flow resulting in avascular necrosis. The image to the left shows some of that vascular in-flow pattern.
The Hawkin’s classification of talar neck fractures
Talar fractures are described by the Hawkins classification. In the Hawkins classification, all stage, 1-4, have the primary fracture line within the neck of the talus. With increased force applied to the fracture, dislocation of the talus from adjacent bones becomes more complex, therefore increasing the risk of avascular necrosis. (1)
Hawkin’s classification and rates of avascular necrosis
Hawkins 1: 0- 13%
Hawkins 2: 20- 50%
Hawkins 3: 20-100%
Hawkins 4: 75-100%
What is avascular necrosis of the talus?
That little bullet hole in the first image says it all. That one image captures the location of the nutrient, or most significant artery that supplies blood flow to the talus. Avascular necrosis is the term used to describe loss of blood flow to bone. If the bone, and in the case, the talus, looses blood supply, the bone dies and collapses. The only solution is a pantalar fusion, fusing the heel bone (calcaneus) to the leg bone (the tibia).
In my book, that’s a bad day.