Ankle Arthritis: A Brief Overview

An introduction to Ankle Arthritis

Diagram of the bones that compose the ankle.
Diagram of the bones that compose the ankle.

Ankle osteoarthritis is an interesting topic because it is very different than the osteoarthritis that affects the hip and knee. Before we delve into the topic, let’s begin by reviewing the basic anatomy. The ankle joint is made up of three bones: the tibia (shin bone), the fibula (the smaller bone sitting toward the outside of the leg), and the talus (saddle-shaped bone that articulates with the tibia).

These three bones make up the tibiotalar joint, which is another name for the ankle joint.

Now that we have the terminology down, lets talk about what makes ankle arthritis so unique. Osteoarthritis of the ankle is about nine times less common than OA of the knee or hip. The most common reason for developing arthritis of the ankle is prior trauma. Other reasons include altered mechanics of the ankle, inflammatory conditions such as rheumatoid arthritis, infection, or neuropathic conditions such as charcot-marie-tooth disease (a condition that involves muscle dysfunction and lack of sensation throughout the foot).

Traumatic injuries to the ankle, such as different types of ankle fractures, are by far the most common reason for developing arthritis of the ankle joint. We don’t have the exact reason for why ankles are prone to developing arthritis after trauma, but a few theories exist. The first theory suggests that the energy of the original trauma causes damage to the cartilage, that later predisposes that cartilage to developing arthritis.

The other theory suggests that maybe it is the small step-offs in cartilage that are left after an ankle is fractured, and then the bones put back in place, that slowly over time damage the cartilage and lead to OA. Neither or both of these theories could be true.

Post-traumatic ankle OA typically develops within two years of the injury.

Studies suggest that if OA is not present at 2 years after injury, it is unlikely to develop within the next 5-10 years. Post-traumatic arthritis of the ankle can develop after a number of ankle fracture types. Whether you injure the fibula, tibia, tibial plafond (the ‘roof’ that is covering the talus) or the talus itself, post-traumatic OA can develop. Certain fractures, such as fractures of the talar neck are associated with very high rates of post-traumatic OA due to the extent of injury to the cartilage.

The cartilage lining the ankle is quite unique. It is thin, ranging from 1 to 1.7mm, much thinner than that of the knee. A proposed theory for this design is that the thin cartilage does a better job at distributing the stress across the joint surface. The ankle experiences a great deal of force with every step a person takes. The ankle experiences loads up to five times our body weight with every step. This makes the ability of the joint to evenly distribute that stress all the more important.

If, for example, the shape of the ankle joint is altered by a fracture that healed in slightly imperfect position, the mechanics of the ankle, and its ability to distribute the stress of walking become altered.

Studies show that ankle cartilage is less affected by age compared to cartilage of the hip. This may explain why rates of osteoarthritis of the ankle are significantly lower than those for the hip. The cartilage lining the talus is especially tough and more resistant to indentation than that of other joints like the knee. These are some of the reason why ankle arthritis is so much more rare comparing to knee or hip arthritis. While approximately 10% of people over 65 have knee arthritis, ankle arthritis is 8 to 9 times more rare; an ankle fusion or replacement, two common treatment options for end-stage ankle arthritis, are performed twenty-four times less frequently than total knee replacements.

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