MRI imaging of the normal infant hip: measurement of acetabular coverage

Purpose: To define with MR imaging a reference value for acetabular coverage on coronal and sagittal images for a population of healthy children. Materials and Methods: 36 children (72 hips) where prospectively studied over 1 year. T1-weighted spin-echo images in both coronal and sagittal planes were obtained. Slice thickness was 4mm, Measurement of acetabular coverage (AHI: Acetabular-Head Index) was made in both planes with two different landmarks: bone and cartilage. Study of the evolution with age was made. Results: The acetabular coverage is symmetrical and decreases with age. Its measurement is reproducible, Conclusion: This study shows that measurement of acetabular coverage (AHI) is easily obtained at MR imaging and is reproducible. We suggest 83 (mean 1SD) as the inferior limit for AHI based on cartilage measurements. We introduce sagittal values, never published, We believe that MR, by its ability to demonstrate the cartilaginous surfaces, will play a major role in the true understanding of the anatomical relationship between the femoral head and the acetabulum.