Marfan's syndrome is an autosomal dominant disorder of connective tissue, 
commonly involving the cardiovascular, ocular, and skeletal systems. Revised 
criteria for the clinical diagnosis of Marfan's syndrome regard skeletal 
involvement as a major criterion if at least four of eight typical skeletal 
manifestations are present, one of which is protrusio acetabuli. Using Kulman's 
method to determine the presence of protrusio, we analysed the pelvic X-rays of 
15 patients with Marfan's syndrome and 15 controls. Protrusio was present in 47% 
(7/15) of Marfan patients, compared with 7% (1/15) of controls (P = 0.035). 
Using the revised criteria, the presence of protrusio would have affected the 
final diagnosis of Marfan's syndrome in only one patient out of 15. Therefore, 
we recommend that a pelvic X-ray is reserved for those cases in which the 
presence of protrusio will alter the final diagnosis. With regard to the 
radiological assessment of protrusio, in our opinion this can be performed 
simply and reliably using the position of the acetabular line alone.