Normal Talar Dome–Tibial Plafond Distance on Radiography
The talar dome–tibial plafond distance refers to the joint space measured between the superior articular surface of the talus and the distal tibial articular surface (plafond) on ankle radiographs. Accurate measurement of this interval is essential for evaluating lateral ligamentous integrity and diagnosing mechanical ankle instability.
Normal Reference Values
| Orientation | Location | Measurement |
|---|---|---|
| Anteroposterior | Varus Stress (Instability) | _ >3 mm |
Clinical Significance
Under physiologic loading, the tibiotalar joint space is symmetric and uniform. During a varus stress radiograph, abnormal tilting of the talar dome away from the tibial plafond indicates disruption of the lateral ligament complex, most commonly the anterior talofibular ligament (ATFL) and calcaneofibular ligament (CFL). A talar dome–tibial plafond distance exceeding 3 mm on a varus stress view is considered evidence of significant lateral ankle instability.
Pitfalls include patient guarding, incomplete stress application, and bilateral asymmetry that may be constitutional rather than pathologic. Comparison with the contralateral ankle is strongly recommended, and a side-to-side difference of more than 3 mm is generally considered more reliable than an absolute threshold alone.
- Lateral ligament complex tear (ATFL ± CFL)
- Chronic lateral ankle instability
- Osteochondral lesion of the talus secondary to recurrent instability
- Peroneal tendon pathology associated with instability
- Syndesmotic injury (evaluate separately with mortise view)
Reference: Berquist TH. Imaging of the Foot and Ankle. Lippincott Williams & Wilkins. p. 117 (2010).
Imaging Notes
Varus stress radiographs are obtained in the anteroposterior projection with the ankle in neutral dorsiflexion. Manual or mechanical stress is applied to invert the hindfoot while the leg is stabilized. The talar dome–tibial plafond distance is measured at the point of maximum talar tilt—typically the lateral margin of the joint. A true AP projection is critical; any rotation can artificially widen or narrow the apparent joint space and lead to diagnostic error.
Fluoroscopic stress views can improve reproducibility by confirming adequate force application in real time. Bilateral simultaneous views, when feasible, facilitate direct comparison and help distinguish constitutional laxity from pathologic instability.