The Anatomical Variations of the Posterolateral Tubercle of Talus in Patients with Posterior Ankle Impingement Syndrome

Abstract Background: The most important anatomical variations of the posterolateral talar tubercle that can predispose patients to development of posterior ankle impingement syndrome (PAIS) are an os trigonum and Stieda process. The aim of this study was to elucidate the prevalence of different anatomical variants of posterolateral talar tubercle on CT imaging, their prevalence in patients with PAIS, and to evaluate the risk posed by these anatomical variants to PAIS. Methods: 1478 ankle CT scans were retrospectively reviewed for the different anatomical variants of the lateral talar tubercle, the type and size of os trigonum. In addition, these anatomical differences were assessed in a subgroup of patients with PAIS. Results: Normal sized lateral tubercle was found in 46.1%, Stieda’s process in 26.1%, os trigonum in 20.5% and almost absent tubercle in 7.3%. A statistically higher prevalence of Stieda’s process was found in males while os trigonum was higher in females (p<0.05). In patients with PAIS, the most common variant was os trigonum (48.8%), followed by Stieda process (34.1%). Patients with Stieda process were 1.5 times more likely to have PAIS, and patients with os trigonum were 4.4 times more likely to have PAIS. PAIS was observed in 20.8% of patients with os trigonum. Fused forms of os trigonum (by cartilage) and sizes larger than 1cm were associated with a higher risk of occurrence of PAIS (OR 2.10 and OR 1.96 respectively)(p<0.05). Conclusion: Patients with os trigonum, followed by Stieda process were more likely to have PAIS compared to other anatomical variants of lateral talar tubercle.