Normal Tibial Torsion Angle Size on CT and MRI
The tibial torsion angle describes the axial rotation of the tibia between its proximal and distal articular axes, reflecting the normal external twist of the tibial shaft. Accurate measurement is essential in the evaluation of rotational limb deformities, particularly in children with in-toeing or out-toeing gait, and in surgical planning for corrective osteotomy.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Axial | 25-55¡ |
Clinical Significance
The accepted normal range for tibial torsion is 25–55° of external rotation. Values below this range indicate internal tibial torsion, a common cause of in-toeing gait in pediatric patients. Excessive external torsion may contribute to out-toeing, patellofemoral malalignment, and anterior knee pain. Tibial torsion abnormalities are frequently encountered alongside femoral anteversion, and the combined rotational profile must be assessed when planning surgical correction.
Key pitfalls include age-related variation — neonates demonstrate relative internal torsion that progressively externalizes through childhood — and inconsistent landmark selection, which can significantly alter measured values. Bilateral comparison is recommended, as asymmetry greater than 10° may be clinically significant even when absolute values fall within the normal range.
- Internal tibial torsion (in-toeing gait, pediatric)
- External tibial torsion (patellofemoral syndrome, out-toeing)
- Post-traumatic rotational malunion
- Cerebral palsy with rotational limb deformity
- Blount disease with associated torsional change
Reference: Shin SY, Yoon CH, Lee ES et al. The availability of radiological measurement of tibial torsion: three-dimensional computed tomography reconstruction. Ann Rehabil Med. 2011;35(5):673-9.
Imaging Notes
On CT, tibial torsion is measured on axial images by calculating the angle between a line through the posterior tibial plateau (proximal reference) and a line through the bimalleolar axis or the posterior talar surface (distal reference). Three-dimensional CT reconstruction improves reproducibility by minimizing partial-volume and positioning errors. The patient should be imaged supine with the lower limbs in a neutral, standardized position.
On MRI, the same axial landmark methodology applies, using axial sequences through the proximal and distal tibia. MRI avoids ionizing radiation and is preferred in younger patients; however, longer acquisition times increase the risk of positional change between proximal and distal acquisitions, so dedicated rotational protocols or simultaneous full-limb coverage are advisable when available.