Fibular hemimelia

Congenital longitudinal deficiency of the fibula (hemimelia) is a congenital deformity, which is characterized by the partial or total absence of the fibula (calf bone).

Fibular hypoplasia: incomplete development of the fibula

Fibular aplasia: 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 partially or completely missing, the back of the foot is no longer held in the malleolar fork. The foot "flaps around" and is unstable (lateral luxation). Fibular hemimelia is always associated with a reduced longitudinal growth of the lower leg. Antecurvation (bending) of the tibia (shin bone) is common, probably due to the strong pull of the connective tissue nature of the calf bone (fibular ray).

 

Congenital longitudinal deficiency of the fibula is the most common congenital deformity of the long bones. It occurs in 7.4 to 20 out of 1,000,000 newborns. The cause remains unknown. 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 facing the knee is less developed and slightly shorter.

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

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

Type Ia Type Ib Type II

 

Congenital longitudinal deficiency of the fibula is often associated with:

  • Leg length discrepancy
  • Malformation of the femur
  • Malformation of the knee joint
  • Absence 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 in accordance with the ball and socket principle
  • Equinovalgus deformity of the feet
  • Missing toes
  • Further defects of the forefoot and/or rearfoot

In rare cases, it may also be associated with a defect of the ulna (a bone of the forearm) and is then called FFU syndrome.

Clinical picture

Depending on the severity of the defect, children with a congenital deficiency of the fibular 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 shape and position of the foot may be notably different; 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.

Apart from the defects listed above, the patient is in good health and does not have any additional disorders. The mental development is not impaired.