Isolated fibular hemimelia (ORPHA:93323)
A rare congenital limb malformation characterized by complete or partial absence of the fibula bone combined with dysplasia and hypoplasia of the tibia and dysplasia, hypoplasia or aplasia of parts of the foot.
Epidemiology
Fibular hemimelia incidence is reported to be between 1/50,000 and 1/135,000 births. A slight male preponderance has been reported in some studies, whereas other reports describe an equal sex distribution.
Clinical description
Unilateral involvement is found in most cases. Bilateral fibular hemimelia is rare. Fibular hemimelia may vary from partial absence of the fibula with mild shortening and a relatively normal-appearing limb, to absence of the fibula with severe shortening and pro-curvatum of the tibia, knee joint instability and foot and ankle deformity. The foot frequently shows deficiency of the lateral rays with or without tarsal coalitions, and an equinovalgus position. Clubfoot-type fibular hemimelia presents with a clubfoot-like foot deformity. Shortening of the leg results from a constant growth inhibition that allows for prediction of leg length discrepancy at maturity. In many cases, fibular hemimelia is associated with congenital femoral deficiency of the femur (CFD), which can be very mild with only mild shortening and distal femur valgus. Most cases do not show any additional anomalies or other birth defects. In rare cases other skeletal anomalies (craniosynostosis, syndactyly, brachydactyly, oligodactyly and ectrodactyly) may be present. Fibular hemimelia can also be found in generalized skeletal dysplasias and dysostoses. Very rarely, fibular hemimelia is associated with non-skeletal malformations (eye abnormalities such as anterior chamber anomalies or anophthalmia, cardiac anomalies, renal dysplasia, thrombocytopenia, thoracoabdominal schisis, spina bifida).
Etiology
The etiology is unclear. The deformity is probably due to disruptions during the critical period of embryonic limb development, between 4th and 7th week of gestation. A somatic gene mutation has been suggested.
Diagnostic methods
Diagnosis is based on clinical examination and X-rays.
Differential diagnosis
Differential diagnoses include skeletal dysplasias and dysostoses with asymmetrical involvement of the lower limbs such as femoral-facial syndrome.
Antenatal diagnosis
Prenatal diagnosis of fibular hemimelia has been reported. The rate of true positive prenatal diagnosis is depending on the severity of shortening and the presence of foot anomalies like absent rays or clubfoot.
Genetic counseling
Most cases are sporadic. A family history has been reported in a small percentage of cases with an autosomal dominant pattern of inheritance and incomplete penetrance.
Management and treatment
Management requires a multidisciplinary approach (genetic counselors, pediatric orthopedic surgeons,). Orthopedic treatment aims at correcting the leg length discrepancy, and, in bilateral cases, correcting the asymmetrical dwarfism. However, the functional outcome in more severe cases is primarily depending on correction and management of the deformities and anomalies at the knee and foot and ankle. In less severe cases with minimal hypoplasia of the fibula and a stable knee and foot and ankle, simple bone lengthening is used to equalize limb length. In moderate to severe fibular hemimelia, limb lengthening needs to be combined with a correction of the complex deformities at the foot and ankle. If instability at the knee joint is clinically significant it also needs to be addressed with reconstructive procedures. Very rarely, for cases with most severe shortening and a non-functional foot, amputation with prosthetic fitting in early childhood may be considered. However, even then tibial procurvatum and knee flexion contracture need to be addressed.
Prognosis
Fibular hemimelia is usually a benign condition, although severe cases might need multiple surgeries throughout childhood. The functional result mostly depends on the status or quality of reconstruction of the knee and foot and ankle. In case of syndromic presentation, prognosis depends on the nature of the associated anomalies.

                            Last update: 
                            August 2020


                            - Expert reviewer(s): 
                            Pr Sebastian FARR  - Pr Christof RADLER