The Acetabular Index and the Physeal Angle of the proximal femur are a radiographic assessment of the morphology of the acetabulum and the proximal physis, respectively. Their values to decrease with age and it remains unknown whether any correlation exists between them or if weightbearing has any influence. X-rays belonging to 30 infants (60 hips), 4 boys and 26 girls, were studied between 2003 and 2006, measuring the Acetabular Index (AI) and the Femoral Proximal Physeal Angle (PPA). Measurements were taken using a goniometer (error ± 1°). All the cases had ultrasound scans at 4 months of age, with alpha angles smaller than 50° (Graf type IIa) and cephalic coverage between 33% and 50%. Anteroposterior hip X-rays were taken at 3 months (pre-weightbearing) and 4–10 months (post-weightbearing). Statistics: t-Test and correlation.

The AI was 21.5° (19.5° boys, 21.8° girls) pre-weightbearing and 20.9° (20.8° boys, 21° girls) post- weightbearing. The PPA was 76.5° (75.9° boys, 76.6° girls) pre-weightbearing and 74.9° (75.5° boys, 74.8° girls) post-weightbearing. AI and PPA decreased pre- and post- weightbearing, 2′8% and 2′1% respectively. The decrease was considered significant in the PPA (p = 0.02), especially in girls (p = 0.009), and not significant in the IA. Differences were found between sexes: the AI increased in boys (+6.3%) and decreased in girls (−8.3%), and the PPA decreased in both boys (−0.5%) and girls (−2.3%). The side had no influence. No relevant correlation was found between AI and PPA, both pre- (r = − 0.15, p = 0.27) and post- weightbearing (r = − 0.24, p = 0.07).

We did not find any relevant correlation between IA and PPA values, neither previous to weightbearing, nor in the months after weightbearing occurs. The measured angles suffered a decrease after weightbearing but the only significant decrease was in the PPA.

Purpose: To study the development of the hip and the relationship of radiological angles between acetabulum and proximal femur in children 0–3 years and thus the influence of walking and weight bearing on hip development.

Material and Methods: A study mesuring radiological angles in antero-posterior X-rays of pelvis in 334 children between 0 a 3 years of age (1997–2005), including acetabular index (AI) and physeal proximal angle (PPA (Alsberg’ angle) with goniometer (error ± 1°). Patients with pelvis or femur fractures or inflammatory diseases were excluded. Age distribution was of 1 (69.2%), 2 (22.2%) and 3 years (8.7%). 36.8% were males and 63.2% females. Descriptive statistics, T- test, Spearman correlation and ANOVA were used. Level of significance p< 0.05.

Results: The mean AI was 20.2°, 19.9° and 17.3°, in 1, 2 and 3 years. The AI angle diminishes significatively in children older than 2 years of age (p = 0.002). The mean PPA was 79.5°, 74.9° and 74.2°, in 1,2 y 3 years respectively. The Alberg’s angle reduced significatively at 1 year of age (p = 0.0005). AI and PPA was higher in females after 1 year of age (p = 0.02 and p = 0.04). There are not significative correlation between AI and Alsberg’ angle in different groups of children (r = 0.03). The age was important factor in both angles changes (p = 0.0005), but female patients (p = 0.002) and left side (p = 0.02) influenced only in AI.

Conclusions: AI and PPA angles reduced with age specially in 2 and 1 year, respectively, suggesting the effect of weight bearing and walking on hip shape. There was not relation between both angles in different groups of age.