D'Arcy et al. (1978) studied the family of a girl who between ages 8 and 11 rapidly developed hip pain and stiffness with flexion contractures and protrusio acetabuli. The mother and a brother had limitation of hip motion, ... D'Arcy et al. (1978) studied the family of a girl who between ages 8 and 11 rapidly developed hip pain and stiffness with flexion contractures and protrusio acetabuli. The mother and a brother had limitation of hip motion, while radiologic criteria for protrusio were present in the mother and 4 of the proband's 8 sibs. Only 1 complained of hip pain. At age 16 the proband underwent bilateral hip replacement. The histologic changes were those of fibrocartilaginous replacement and osteophyte formation. The 5 oldest sibs were affected. MacDonald (1971) studied 4 generations of a Scottish family in which all 3 members of the second generation showed marked protrusio acetabulum and members of the other generations had abnormally deep acetabuli. Francis (1959) studied 6 families, finding affected members in 3 generations of one. Rechtman (1936) was first to comment on familiality. Friedenberg (1953) was impressed with an increased frequency in American Blacks. In South Africa an extraordinarily high frequency was found in Bantu as compared with East Indians and Europeans (Crichton and Curlewis, 1962). Ventruto et al. (1980) reported an Italian family with 9 members (and presumably a tenth member) with primary protrusio acetabuli in 4 generations and 6 sibships.