Normal Wiberg's Angle Size on Hip Radiography
Wiberg's center-edge (CE) angle quantifies the lateral coverage of the femoral head by the acetabulum on anteroposterior (AP) pelvic radiography. It is drawn between a vertical line through the center of the femoral head and a line connecting the center of the femoral head to the lateral edge of the acetabulum. Accurate measurement is essential for diagnosing developmental dysplasia of the hip (DDH) and guiding surgical decision-making in pediatric and adolescent patients.
Normal Reference Values
| Orientation | Age | Measurement |
|---|---|---|
| Anteroposterior | 3 months | 18-20¡ |
| Anteroposterior | 2 y/o | 30¡ |
| Anteroposterior | 5-8 y/o | 19¡ |
| Anteroposterior | 9-12 y/o | 25¡ |
| Anteroposterior | 13-20 y/o | 26-30¡ |
Clinical Significance
Wiberg's angle increases with skeletal maturation as the acetabulum deepens and provides greater femoral head coverage. Values below age-expected norms indicate insufficient lateral coverage, predisposing patients to joint instability, early labral pathology, and accelerated osteoarthritis. In adolescents and adults, a CE angle below 20° is generally accepted as indicative of hip dysplasia, while values between 20–25° represent a borderline zone requiring clinical correlation.
Conversely, an excessively large CE angle (>40°) may indicate pincer-type femoroacetabular impingement (FAI), where over-coverage leads to repetitive labral and cartilage damage. Pitfalls include patient rotation on the radiograph, which artificially alters the apparent acetabular margin, and difficulty identifying the true lateral sourcil edge in young children with incomplete ossification.
- Developmental dysplasia of the hip (DDH)
- Legg-Calvé-Perthes disease with femoral head deformity
- Pincer-type femoroacetabular impingement
- Post-traumatic or post-infectious acetabular dysplasia
- Neuromuscular hip dysplasia (e.g., cerebral palsy)
Reference: Ozonoff MB. Pediatric orthopedic radiology. W B Saunders Co. p. 181 (1992).
Imaging Notes
Wiberg's angle is measured on a true AP pelvis radiograph with the patient supine, legs in slight internal rotation (~15°), and the pelvis level without rotation. The angle is formed at the center of the femoral head: one line drawn vertically (parallel to the long axis of the body) and a second line drawn to the superolateral edge of the acetabular sourcil. Precise identification of the femoral head center requires a circle-fitting technique, particularly relevant in young children where ossification is incomplete.
In children under 5 years, the cartilaginous acetabular and femoral head margins are not fully ossified, limiting plain radiograph accuracy; ultrasound or MRI may provide complementary information. Ensure consistent pelvic positioning across serial examinations to allow valid longitudinal comparison of CE angle progression with growth.