Size matters: The influence of the posterior fragment on patient outcomes in trimalleolar ankle fractures.

Introduction: Ankle fractures are increasing in incidence. The more complicated the lesion is, the higher the risk of developing posttraumatic arthrosis. Severe posttraumatic arthrosis results in a reduced quality of life. Therefore, the treatment of a trimalleolar fractures is crucial. However, the treatment guidelines for posterior malleolar fractures (PMF) are still based on recommendations from 1940. Only a few retrospective studies have been conducted, which analysed patient outcomes based on lateral X-rays of the ankle. The purpose of this retrospective analysis was to survey patient outcomes in relation to the size of the PMF on the basis of CT-scans.

Methods: We retrospectively examined 42 patients with trimalleolar fractures with an average follow-up of 2.5 years. Twenty-four patients (57%) received a CT scan of the ankle joint. The radiologic images were analysed for the size of the PMF and the involvement of the joint surface using lateral X-rays and available CT images. We examined all 42 patients clinically and radiologically, and estimated the grade of arthrosis of the ankle in accordance with the Bargon Score and assigned AOFAS Scores for each patient. We divided our patients into different groups according to the size of their PMF and evaluated patient outcomes in accordance with the compiled data first on the basis of X-ray data and then on the basis of CT data.

Results: Comparing the measurement results by two different radiologic methods revealed that CT results in a more precise determination of PMF size in contrast to lateral X-rays, by which measurements were generally overrated. The statistical evaluation of our data demonstrated that patients with an osteosynthesis of the PMF and a PMF size of >25% showed signs of posttraumatic arthrosis but had better outcomes in accordance to the AOFAS score. All results were not significant.

Conclusion: An exact evaluation of CT images of posterior malleolar fractures in patients with trimalleolar ankle fractures is crucial for the decision to perform an osteosynthesis of the PMF and, therefore, an analysis of patient outcomes. The results of previous studies should be evaluated cautiously due to missing CT data. To date, this is the largest retrospective patient series of patient outcomes based on CT data.