Supination External Rotational Ankle Fracture Injury Pattern Correlation With Regional Bone Density

Rotational ankle fractures can present with an array of possible osseous and ligamentous injury combinations in reliable anatomic locations. What accounts for these different injury patterns and whether specific patient and injury factors underlie the different injury patterns is unclear. The purpose of this study was to determine whether causative factors exist that could account for the various injury patterns seen with rotational ankle fractures. A registry of operatively treated supination external rotation stage IV (SER IV) ankle fractures was used to identify patients. Computed tomography imaging was used to calculate regional bone density by using average Hounsfield unit measurements on axial images from the distal tibia and fibula. Patients were grouped into those with no posterior or medial malleolar fracture (equivalent group), those with either a posterior or medial malleolus fracture (bimalleolar group), and those with both posterior and medial malleolar fractures (trimalleolar group). Sixty-seven patients met inclusion criteria. Regional bone density at the ankle, as measured with Hounsfield units, was significantly higher in the equivalent group (371) than in the bimalleolar group (271, P < .0001) and trimalleolar group (228, P < .0001). Logistic regression analyses identified regional bone density as a significant predictor of a medial malleolus fracture (P = .002) and of a posterior malleolus fracture (P = .005). In our cohort of SER IV ankle fractures, regional bone density at the ankle significantly correlated with the presence and number of malleolar fractures compared with ligamentous ruptures. Treating surgeons can use this information to anticipate bone quality during operative fixation based on ankle fracture injury pattern. In addition, the presence of a trimalleolar ankle fracture was a significant indicator of poor bone quality and may represent the first clinical sign of abnormal bone metabolism in many patients. Level III, prognostic retrospective cohort study