Normal Femoral Neck Torsion Angle Size on CT
The femoral neck torsion angle — also called femoral anteversion — describes the angular relationship between the femoral neck axis and the transcondylar axis of the distal femur. Accurate measurement is essential for evaluating rotational limb deformities, guiding surgical planning in developmental dysplasia of the hip, and assessing gait abnormalities in children and adults.
Normal Reference Values
| Age | Measurement |
|---|---|
| Newborn | 34-40¡ |
Clinical Significance
Femoral torsion normally decreases with skeletal maturation, from approximately 34–40° at birth toward adult values typically in the range of 10–15°. Persistent elevated anteversion (>25–30° in older children or adults) is associated with in-toeing gait, patellofemoral malalignment, and increased risk of hip dysplasia. Conversely, reduced anteversion or retroversion may contribute to out-toeing and accelerated hip osteoarthritis.
CT remains the gold-standard modality for quantifying torsion because it avoids the superimposition and positioning errors inherent in plain radiographic techniques. Awareness of age-related normative values is critical: applying adult thresholds to neonatal or pediatric imaging will systematically overdiagnose pathologic anteversion.
- Developmental dysplasia of the hip (increased anteversion)
- Cerebral palsy (typically increased anteversion)
- Slipped capital femoral epiphysis (associated retroversion)
- Post-traumatic malunion of proximal femoral fractures
- Idiopathic in-toeing or out-toeing gait in children
Reference: Mesgarzadeh M, Revesz G, Bonakdarpour A. Femoral neck torsion angle measurement by computed tomography. J Comput Assist Tomogr. 11 (5): 799-803.
Imaging Notes
On CT, the femoral neck torsion angle is measured using two axial reference planes: one through the long axis of the femoral neck and head, and one through the posterior femoral condyles at the knee. Dedicated axial slices through both the proximal femur and distal femur are required; modern scanners allow retrospective multiplanar reconstruction from a single volumetric acquisition, reducing radiation exposure compared with older two-level techniques. Positioning the patient supine with the legs in a neutral, non-rotated position minimizes technique-related error.
Ensure that the femoral neck axis slice captures the true mid-neck rather than an oblique plane, as partial volume averaging at the femoral head–neck junction is a common source of measurement variability. Bilateral measurements should be obtained routinely, as inter-limb asymmetry >10° may carry independent clinical significance regardless of absolute values.