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Femur-fibula-ulna complex

Synonym(s) FFU complex
Femur-fibula-ulna dysostosis
Femur-fibula-ulna syndrome
Proximal focal femoral deficiency
Prevalence 1-9 / 100 000
Inheritance Not applicable
Age of onset Neonatal
  • Q72.8
  • C2363814
  • C537918
  • 10068448


The Femur-Fibula-Ulna (FFU) complex is a rare limb malformation entity characterised by highly variable combinations of congenital anomalies of femur, fibula, and/or ulna, which can appear along with finger/toe anomalies at the ulnar/fibular side. The prevalence of FFU has been estimated as between 0.11 and 0.20 per 10,000 births, with males affected more often than females. Some authors state that FFU complex and Proximal Femoral Focal Deficiency (PFFD) are the same entity, but others discern the two as separate entities. Highly variable, and often rare, anomalies of the arms are particularly frequent in FFU complex, i.e. amelia, hypoplasia of the humerus, and humero-radial synostosis. FFU complex has been classified into four groups, depending on the malformed bones involved: forms with only one affected limb, and forms with two, three or four affected limbs. An extensive study of nearly 500 cases, in which the analysed groups displayed nearly equal proportions of the most common malformations, supported the hypothesis that even if only one arm or one leg is affected, the cases may still be classifiable as FFU complex. An important characteristic is that the limb defects are asymmetrical. Upper limbs are affected more often than lower limbs, and the right side of the body is affected more often than the left. The aetiology remains unknown. FFU is sporadic and recurrence within a sibship is extremely rare. FFU has been reported in one out of a set of monozygotic twins, with the co-twin having ectrosyndactyly of one hand. There has been no maternal or paternal age effect observed. Parental consanguinity does not appear to be an important etiological factor. Some authors support early somatic mutation as a cause of FFU, but this is has not yet been proven. FFU needs to be distinguished from femoral hypoplasia-unusual facies syndrome (FH-UFS), in which bilateral femoral hypoplasia is symmetrical and is associated with facial dysmorphism. It occurs as a separate entity, and has also been attributed to maternal diabetes, or viral disease during pregnancy. Prenatal diagnosis of FFU by ultrasonography has been reported repeatedly in the literature from 20 weeks of gestation onwards. Orthopaedic treatment depends on the type of defects.

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