Background: Protrusio acetabuli is known to occur in patients with Marfan syndrome, but its prevalence, its effects on hip function, and its possible association with the subsequent development of degenerative hip disease have not been studied in a large population. Nevertheless, some clinicians have recommended prophylactic hip surgery for preadolescents with Marfan syndrome and protrusio acetabuli.

Methods: We performed a cross-sectional study of 173 patients (346 hips) with Marfan syndrome who were interviewed and examined for calculation of the Iowa hip score. Anteroposterior radiographs of the pelvis were made, and two radiographic indices of acetabular depth were measured: (1) the center-edge angle of Wiberg and (2) the acetabular-ilioischial distance. The presence of protrusio was defined with use of two extant definitions: (1) a center-edge angle of >50° or (2) an acetabular-ilioischial distance of =3 mm in male patients or =6 mm in female patients. Linear regression analyses were performed between these radiographic indices of acetabular depth and patient age, Iowa hip scores, the magnitude of the radiographic joint space, and range of motion.

Results: The prevalence of protrusio acetabuli was 27% according to the center-edge angle criterion and 16% according to the acetabular-ilioischial distance criterion. The prevalence of protrusio increased until the age of twenty years and remained stable after the age of twenty years. Slight but significant negative correlations were detected between the two radiographic indices of acetabular depth and both the Iowa hip score and the summed range of motion (p < 0.02 for all). No significant relationship was found between the two radiographic indices and pain scores. In patients with Marfan syndrome who were more than forty years old, the Iowa hip scores for hips with protrusio were not significantly lower than those for hips without protrusio.

Conclusions: In patients with Marfan syndrome, the prevalence of protrusio acetabuli increases during the first two decades of life and then plateaus in terms of both population-wide prevalence and radiographic severity. In this population, protrusio generally is not associated with severely problematic hip function but it is associated with slightly decreased range of motion of the hip. We concluded that prophylactic surgical intervention is not indicated for most patients with Marfan syndrome who have a radiographic diagnosis of protrusio.