The comparative morphology of idiopathic ankle osteoarthritis.

Background: Osteoarthritis is the most common joint disease and the leading cause of chronic disability in the U.S. However, symptomatic osteoarthritis at the ankle occurs nine times less frequently than at the knee and hip, even though the ankle experiences greater pressure and is the most commonly injured joint in the human body. This study sought to quantify the shape and coverage of the talar and tibial articular surfaces by comparing the three-dimensional morphology of the ankle in patients with ankle osteoarthritis and in those without arthritis, including a subset of different foot shapes.

Methods: We created three-dimensional models of the joint surfaces of ankles with and without arthritis. We fit cylinders to the joint surfaces, and measured the radius of the tibial and talar articular surfaces, the tibial coverage angle of the talus, and the degree of joint skew. We hypothesized that these measurements would be different between those with and without ankle osteoarthritis and among foot types. We evaluated a total of 108 limbs.

Results: The mean tibial and talar radii were significantly higher and the mean coverage angle was significantly lower in feet with ankle osteoarthritis than in all other foot categories. The mean coronal skew in limbs with ankle osteoarthritis was significantly higher than in the neutral and flatfoot groups. The high arched feet had several significantly different skew angles from other foot types. No significant differences in joint morphology measures between neutrally aligned feet and flatfeet were found.

Conclusions: Ankles with osteoarthritis had larger tibial and talar radii, a smaller coverage angle, and larger skew angles than ankles without osteoarthritis. Together, these findings suggest a flatter ankle joint with less stability, depth, and containment and reduced articular constraint and support.