Normal CFL/ATFL Angle Size on MRI: Reference Values
The calcaneofibular ligament (CFL) and anterior talofibular ligament (ATFL) are the primary stabilizers of the lateral ankle, and the angle formed between them is an important anatomical parameter. Measuring the CFL/ATFL angle on MRI helps define normal ligament orientation and guides interpretation of lateral ankle instability.
Normal Reference Values
| Measurement |
|---|
| 70¡-140¡ |
Clinical Significance
The CFL/ATFL angle reflects the geometric relationship between these two critical lateral ankle ligaments. A normal angle of 70°–140° encompasses a wide physiological range, reflecting natural anatomical variation between individuals. Accurate knowledge of this range is essential when evaluating ligamentous integrity, particularly following inversion injuries — the most common mechanism of ankle sprain.
Disruption or abnormal orientation of either the CFL or ATFL can compromise lateral ankle stability. MRI allows direct visualization of ligament continuity, signal intensity, and angular relationships. Morphological abnormalities — thickening, waviness, discontinuity, or periligamentous edema — are more diagnostically significant than isolated angular deviation, but the angle provides useful anatomical context, particularly in pre-operative planning for ligament reconstruction.
- ATFL tear: Most commonly injured ligament in lateral ankle sprains; associated with inversion/plantarflexion mechanism
- CFL tear: Often injured in combination with ATFL in higher-grade sprains
- Chronic lateral instability: Recurrent sprains with laxity of CFL and/or ATFL
- Anatomical variant: Accessory ligaments or bifid ATFL may alter perceived angle
- Post-surgical anatomy: Brostrom-type repair can alter normal ligament orientation
Reference: Stoller DW, Tirman PF, Bredella MA. Diagnostic imaging, Orthopaedics. Amirsys Inc. p. 6(31) (2004).
Imaging Notes
On MRI, the CFL/ATFL angle is best assessed on axial or oblique axial sequences through the lateral ankle. Proton density fat-suppressed or T2-weighted sequences provide optimal ligament-to-background contrast. The ATFL is typically identified coursing from the anterior fibular tip to the talar neck, while the CFL runs from the fibular tip inferoposteriorly to the lateral calcaneus. The angle is measured at their fibular origin. Thin-section imaging (2–3 mm slice thickness) and correct foot positioning in neutral dorsiflexion reduce partial volume averaging and optimize ligament depiction.