Normal Hip Neck Shaft Angle Size on Radiography
The neck shaft angle (NSA), also called the cervicodiaphyseal angle, is the angle formed between the femoral neck axis and the femoral diaphyseal axis on anteroposterior (AP) pelvic or hip radiographs. Accurate measurement is essential for evaluating hip morphology, diagnosing developmental and degenerative conditions, and planning surgical or corrective interventions.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Anteroposterior | 110-140¡ |
Clinical Significance
A normal neck shaft angle of 110–140° reflects typical femoral geometry. When this angle falls below 110°, the condition is termed coxa vara, characterized by a relatively horizontal femoral neck. This reduces the mechanical advantage of the hip abductors, shortens the limb, and increases stress across the femoral neck. Angles exceeding 140° define coxa valga, which alters load distribution and may predispose to hip instability or acetabular dysplasia.
The NSA naturally decreases with age: neonates present with relatively high angles (around 150°) that gradually reduce to the adult range. Failure of this normal developmental reduction should prompt further assessment. Pitfalls include patient rotation on the radiograph, which can spuriously alter the measured angle, and asymmetric positioning of the lower limbs.
- Coxa vara — NSA <110°; causes include rickets, Paget disease, developmental dysplasia, and prior fracture
- Coxa valga — NSA >140°; associated with neuromuscular conditions and hip dysplasia
- Developmental dysplasia of the hip (DDH) — frequently accompanied by abnormal NSA
- Femoral neck stress fracture — coxa vara may be a predisposing factor
- Slipped capital femoral epiphysis (SCFE) — progressive varus deformity on follow-up imaging
Reference: Scheuer L, Black S. Developmental Juvenile Osteology. Academic Press. (2000).
Imaging Notes
The neck shaft angle is measured on a true anteroposterior radiograph of the pelvis or hip, with the patient supine, lower limbs internally rotated approximately 15–20° to correct for femoral anteversion and profile the femoral neck optimally. A line is drawn along the central axis of the femoral neck and a second line along the femoral diaphysis; the angle subtended at their intersection is the NSA. Bilateral comparison on a single AP pelvis view is preferred to ensure symmetry and minimize projection error.
Consistent patient positioning is critical — even mild external rotation can artificially reduce the apparent angle, mimicking coxa vara. If the lesser trochanter is prominently visible, external rotation should be suspected and positioning corrected before measurement is recorded.