Syndesmotic Stabilization in Pronation External Rotation Ankle Fractures

Boden et al. suggested syndesmosis fixation was not necessary in distal pronation external rotation (PER) ankle fractures if rigid bimalleolar fracture fixation is achieved and was not necessary with deltoid ligament injury if the fibular fracture is no higher than 4.5 cm of the tibiotalar joint. We asked whether height of the fibular fracture with or without medial stability predicted syndesmotic instability as compared with intraoperative hook testing in these fractures. We reviewed 62 patients (35 male, 27 female) with a mean age of 45.6 years (range, 19–80 years). Using a bone hook applied to the distal fibula with lateral force to the distal fibula in the coronal plane, we fluoroscopically assessed the degree of syndesmosis diastasis in all patients. The mean height of the fibular fracture in patients with a positive hook test was higher than in patients with a negative hook test (54.2 mm; standard deviation [SD], 29.3 versus 34.8 mm; SD, 21.4, respectively). The height of the fibular fracture showed a positive predictive value of 0.93 and a negative predictive value of 0.53 in predicting syndesmotic instability; specificity of the criteria of Boden et al. was high (0.96). However, sensitivity was low (0.39) using the hook test as the gold standard. The criteria of Boden et al. may be helpful in planning, but may have some limitations as a predictor of syndesmotic instability in distal PER ankle fractures.