The horizontal calcaneofibular ligament: a sign of hindfoot valgus on ankle MRI.

Hindfoot valgus malalignment has been assessed on coronal MRI by the measurement of the tibio-calcaneal (TC) angle and apparent moment arm (AMA). This study aimed to determine if the calcaneofibular ligament (CFL) angle could be used as a further marker of hindfoot valgus malalignment on routine non-weight-bearing ankle MRI. One hundred ninety-five consecutive 3-T ankle MRI studies were identified from the hospital PACS system. The TC and CFL angles could be measured in 155 cases (78%), and the AMA on 153 cases. The study group comprised 56 males and 72 females with a mean age of 46 years (range 4-89 years). In 27 patients, both ankles had been imaged. The Pearson correlation between the TC and CFL angles was -0.43, with a corresponding p value of 0.001 indicating a strong negative correlation between the TC and CFL angles. The CFL angle was significantly lower in those with hindfoot valgus (113 ± 14) compared with those without (123° ± 15°) (p = 0.001). The optimal cut-off point of the CFL angle for hindfoot valgus was ≤119°, with a sensitivity and specificity of 66% and 63% respectively. The Pearson correlation between the CFL angle and AMA was -0.10, with a corresponding p value of 0.21 indicating a weak negative correlation that did not reach statistical significance. Hindfoot valgus as estimated by the increased TC angle on coronal non-weight-bearing ankle MRI is associated with a reduced CFL angle on sagittal MR images, but is not associated with AMA. Therefore, a horizontal orientation of the CFL on sagittal MR images may be a further useful sign of hindfoot valgus.