Fibular hemimelia

The longitudinal fibular defect (hemimelia) is a congenital deformity, which is characterized by the complete lack of the fibula (calf bone) or a part of the fibula.

Fibular hypoplasia: incomplete development of the fibula

Fibularaplasia: complete absence of the fibula

Frequently, fibular hemimelia is associated with additional deformities at the back of the foot and/or fibular ray defects of the foot (missing toes). If the fibula is missing completely or in part, the back of the foot is not held in the malleolar fork any longer. The foot "flaps around" (lateral luxation). The fibular defect is always associated with a reduced longitudinal growth of the lower leg. Probably due to the strong pull of the connective tissue nature of the calf bone (fibular ray), antecurvation (buckling) of the tibia (shin bone) is common.

 

The longitudinal fibular defect is the most common congenital deformity of the long bones. It occurs in 7.4 to 20 of 1,000,000 newborn children. The cause is still unknown so far. The severity of the disorder depends on the extent of the  defect.

Although it does not appear sufficient for therapeutic purposes, a practical classification was proposed by ACHTERMAN and KALAMCHI (1979). This classification is based on the extent of the decrease in length:

Type I: includes all fibular defects, in which a part of the fibula is present (fibular hypoplasia). The two subgroups differ only in the extent of the decrease in length.

In type Ia, the X-ray image shows that the end of the fibula towards the knee is formed more weakly and is slightly reduced in length.

In type Ib, this part of the fibula cannot be detected on the X-ray image.

Typ II, fibular aplasia, designates a complete absence of the fibula.

Type 1a Type 1b Type 2

 

The longitudinal fibula defect is often associated with:

  • Leg length discrepancy
  • Malformation of the upper thigh
  • Malformation of the knee joint
  • Lack of the anterior and/or posterior cruciate ligament
  • Knee instability
  • Curvature of the tibia
  • Ossification of the subtalar joint (subtalar synostosis)
  • Malposition of the ankle following the ball and socket pattern
  • Equinovalgus deformity of the feet
  • Missing toes
  • Further  defects of the forefoot and/or hindfoot

In rare cases, it may be associated with a defect of the ulna of the lower arm and is then called FFU syndrome.

Clinical picture

Depending on the severity of the defect, children with a fibular defect show a more or less pronounced decrease in leg length on the affected side. The knee is hypermobile. The tibia is often curved backwards to the foot and shows a dimple at the bending point of curvature. The foot can be clearly modified in form and position, usually one or more toes are missing.

If both legs are affected, the difference in leg length is usually insignificant. However, a disproportionality between the length of the lower extremities and the trunk is noticeable.

Aside from defects listed above, the patients are in full health and do not have further disorders. The mental development is not impaired.