Protrusio Acetabuli in Osteogenesis Imperfecta: A Two-Center Study on Incidence and Associated Factors.

Osteogenesis imperfecta (OI) is a rare genetic connective tissue disorder characterized by increased fracture risk and bone deformity. Protrusio acetabuli (PA) is a well-recognized radiographic finding in patients with OI, yet data on its incidence, severity, and associated factors across different OI phenotypes remain limited. This retrospective study evaluated pelvic radiographs and clinical data of patients with OI treated in two centers. PA was assessed using established radiographic criteria and graded according to the Sotelo-Garza/Charnley classification. Demographic and clinical variables were analyzed to identify factors associated with PA. Of 69 patients included, PA was found in 32 (46.4%), of whom nine presented with severe, 15 with moderate, and eight with mild PA. Patients with PA were significantly older than those without PA. Univariable logistic regression identified female sex, body mass index > 25 kg/m2, and scoliosis as factors significantly associated with PA. PA is a frequent radiographic finding in OI, affecting patients across all phenotypic severities, including mild disease, and may represent an underrecognized manifestation across the disease spectrum. While several factors were associated with its presence, these findings should be interpreted descriptively. Given the potential for selection bias, the reported prevalence may not be generalizable to the broader OI population. Further prospective studies are required to clarify the clinical relevance and natural history of PA in OI.Level of Evidence IV.