A New Reference to Evaluate Syndesmosis in Sagittal Plane Radiographs of the Ankle: The Lateral Posterior Ankle Ratio.

Abstract

Confirmation of anatomical reduction of ankle syndesmosis is mandatory because improper reduction leads to poor functional results. Coronal plane evaluation of syndesmosis is well described in the literature, but there is little information about sagittal plane evaluation. We sought to evaluate the relationship of fibula and tibia in the sagittal plane and create a new reference that can be applied easily and reliably. Lateral ankle radiographs of 337 individuals with no history of ankle fracture were evaluated. A line was drawn between the anterior and posterior cortices of the distal lateral tibia, and the length of this line was measured (line 1). The distance between the anterior and posterior cortices of the fibula on this line was measured, and the center of this second distance was identified and marked. The posterior half of the fibular width was divided by line 1 and was named the lateral posterior ankle ratio (LPAR). Statistical analysis was performed by side and sex. Mean patient age was 38.6 years; mean LPAR was 0.48. There was a significant difference between men and women by age (P < .001) and LPAR (P = .01). There was no significant difference between right and left ankles by age (P = .63) and LPAR (P = .64). The LPAR was less than 0.40 in 6.8% of the radiographs, 0.40 to 0.50 in 57.9%, and greater than 0.50 to 0.60 in 32.9%. The LPAR should approximate 50% in normal lateral ankle images and, by extrapolation, after syndesmotic reduction.