Normal Fibular Angle Size on Radiography
The fibular angle describes the obliquity of the distal fibula relative to the tibial plafond, measured on anteroposterior (AP) or mortise radiographs of the ankle. Accurate assessment of this angle helps determine whether the fibula is appropriately positioned in length and rotation within the ankle mortise. This measurement is particularly valuable in the setting of ankle trauma and surgical planning for fibular fractures.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Anteroposterior, Mortise | 43-63¡ |
Clinical Significance
The fibular angle reflects the normal downward and lateral orientation of the distal fibula. Values outside the 43°–63° range may indicate fibular shortening, malrotation, or syndesmotic disruption. A decreased angle (more horizontal fibula) is associated with lateral malleolar fractures that have healed in a shortened position, compromising the lateral buttress of the mortise and predisposing to post-traumatic osteoarthritis.
An increased or asymmetric fibular angle compared with the contralateral side warrants further evaluation. Common clinical scenarios and differential considerations when the fibular angle is abnormal include:
- Fibular shortening following malunited Weber B or C fractures
- Syndesmotic injury with proximal fibular migration
- Developmental dysplasia of the ankle in pediatric patients
- Chronic lateral ankle instability with subtle fibular positional changes
- Post-operative assessment after open reduction and internal fixation of fibular fractures
Reference: Keats TE, Sistrom C. Atlas of Radiologic Measurement. Mosby Inc. (2001).
Imaging Notes
The fibular angle is measured on a true AP or mortise view of the ankle. The mortise view, obtained with 15°–20° of internal rotation, eliminates fibular overlap with the talus and provides a clearer assessment of the distal fibular orientation relative to the tibial plafond. The angle is formed between the long axis of the distal fibular shaft and the horizontal line along the tibial articular surface.
Consistent positioning is essential; even minor rotation can alter the apparent angle by several degrees. Comparison with the contralateral ankle using identical positioning significantly improves diagnostic accuracy when unilateral pathology is suspected.