The fibular hemimelia is a congenital longitudinal limb defect presenting with aplasia or hypoplasia of the fibular bone. In two-thirds of patients, only one side is affected, the right leg more often than the left.
It rarely occurs in isolation, usually in combination with other malformations (proximal femoral defect, malformations of the foot and toes, curved tibia, shortening of the entire lower leg). It can also lead to enormous instability in the knee and ankle and significant changes in the soft tissues.
The most important functional disorders are the different leg length in one-sided cases and the asymmetrical short stature in bilateral cases. The foot is usually in Equinovalgus position. Since the affected bone has only a low growth potential, the deformity tends to increase with age.
The following forms can be distinguished:
In Type IA, there is proximal fibular hypoplasia, and the ankle fork is intact.
Type IB is similar to IA, but there is a malformation of the ankle fork.
Type II has a complete aplasia of the fibula.
The etiology of the disease is unclear. The deformity is probably due to a disruption in the critical period of the embryonic development of the limbs (between the 4th and 7th week of pregnancy). Vascular dysgenesis, virus infections, trauma and environmental influences are discussed as possible causes.
Most cases are sporadic. In a few percent of published cases a familial occurrence with autosomal dominant heredity and incomplete penetrance was seen.