Normal Wiberg Angle Size on Hip Radiography
The Wiberg center-edge (CE) angle quantifies the lateral coverage of the femoral head by the acetabulum on anteroposterior pelvic radiography. It is measured as the angle between a vertical line through the center of the femoral head and a line from that center to the lateral edge of the acetabular sourcil. Accurate measurement is essential for identifying hip dysplasia, which predisposes to early osteoarthritis, and for planning corrective procedures such as periacetabular osteotomy.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Anteroposterior | 25-40¡ |
Clinical Significance
A normal Wiberg CE angle ranges from 25° to 40°. Values below 25° indicate lateral undercoverage of the femoral head, consistent with acetabular dysplasia, and are associated with increased joint contact stress, labral tears, and accelerated cartilage degeneration. Values above 40° suggest overcoverage (pincer-type femoroacetabular impingement), which can cause labral damage through repetitive abutment.
Borderline dysplasia is commonly defined as a CE angle of 20–25°, a range that warrants close clinical correlation and often further cross-sectional imaging. Patient age, symptoms, and activity level all influence management decisions in this gray zone.
- Acetabular dysplasia — CE angle <20–25°
- Borderline dysplasia — CE angle 20–25°
- Pincer FAI / overcoverage — CE angle >40°
- Post-traumatic deformity — asymmetric reduction in CE angle
- Perthes disease sequelae — reduced CE angle secondary to femoral head deformity
Reference: Callaghan JJ, Rosenberg AG, Rubash HE. The Adult Hip. Philadelphia, Pa.; Lippincott Williams & Wilkins, c2007. (2007).
Imaging Notes
The Wiberg CE angle is assessed on a standing or supine anteroposterior (AP) pelvis radiograph. The pelvis must be non-rotated, with the coccyx aligned over the pubic symphysis, and the lower limbs in 15° of internal rotation to profile the femoral necks. Rotation or tilt will artificially alter the apparent acetabular coverage, leading to under- or over-estimation of the CE angle. Identify the center of the femoral head using a best-fit circle (Mose template or digital overlay), draw a true vertical line through this center, then extend a second line to the lateral sourcil margin; the angle between these lines is the CE angle.
Bilateral measurements should always be obtained, as asymmetry may be the first clue to unilateral pathology. When plain radiographic findings are equivocal, CT or MRI can provide three-dimensional acetabular coverage assessment and evaluate associated labrocartilaginous pathology.