Normal Distal Tibial Angle Size on Radiography
The distal tibial angle (DTA) describes the inclination of the tibial plafond relative to the long axis of the tibia, measured on anteroposterior or mortise ankle radiographs. It serves as a reliable indicator of coronal ankle alignment and articular congruence. Accurate measurement is essential in evaluating traumatic, degenerative, and post-surgical ankle conditions.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Anteroposterior, Mortise | 45-65¡ |
Clinical Significance
A normal distal tibial angle of 45–65° reflects appropriate tibial plafond orientation. Deviation outside this range may indicate varus or valgus tilt of the distal tibia, which can arise from malunited fractures, physeal growth disturbances, or degenerative joint remodeling. In pre-operative planning for total ankle arthroplasty or supramalleolar osteotomy, the DTA guides correction and implant positioning.
Values below 45° suggest excessive valgus inclination of the plafond, while angles above 65° may reflect varus deformity. Even subtle malalignment can accelerate asymmetric cartilage wear and contribute to ankle osteoarthritis. Serial measurements are useful for monitoring progressive deformity in conditions such as post-traumatic arthritis or chronic ligamentous instability.
- Malunited distal tibial fracture
- Physeal arrest with angular deformity
- Varus or valgus ankle osteoarthritis
- Degenerative or post-traumatic plafond remodeling
- Pre-operative planning for supramalleolar osteotomy
Reference: Keats TE, Sistrom C. Atlas of Radiologic Measurement. Mosby Inc. (2001).
Imaging Notes
The distal tibial angle is measured on a true anteroposterior or mortise view of the ankle with the patient weight-bearing when clinically feasible, as loading more accurately reflects functional alignment. The angle is formed between a line drawn along the tibial shaft axis and a line tangent to the subchondral surface of the tibial plafond. Proper positioning is critical — even minor rotation can artificially alter the apparent plafond inclination and lead to measurement error.
On the mortise view (15–20° internal rotation), the tibiotalar joint space should appear symmetric and the fibula should not overlap the talus, confirming adequate positioning before committing to the measurement. Consistent technique across serial studies is strongly recommended to ensure valid comparison over time.