Fibular hemimelia is a congenital lower limb anomaly characterized by partial or complete absence of the fibula and includes a spectrum ranging from mild fibular hypoplasia to complete fibular aplasia ¹.

Epidemiology

Although rare, it is the most common congenital absence of long bone of the extremities ². The incidence has been suggested to be approximately 5.7-20 cases per 1 million births ³. This condition is twice as common in boys as in girls.

Associations

Fibular hemimelia is commonly associated (>90%) with cruciate ligament dysplasia ⁷, but it is otherwise usually an isolated anomaly that occurs sporadically ^ref. However, it can also be associated with proximal focal femoral deficiency, absence of lateral rays and phalanges of lateral toes 1, syndactyly, and polydactyly ⁴.

Clinical presentation

Fibular hemimelia is usually obvious at birth with limb shortening and limb-length discrepancy ². Syndactyly, oligodactyly, or polydactyly may also be present ⁴. It may also be detected antenatally during obstetric ultrasound evaluation for fetal anomalies ³.

Pathology

Several theories have been put forward to explain this condition, such as defects in the apical ectoderm ridge or defects secondary to an absent anterior tibial artery ³. Amniotic bands may be a factor causing insult to the growing limb bud in utero resulting in this condition ⁴. There has been a case of congenital absence of femur and fibular hemimelia related to maternal hyperpyrexia ⁵.

Classification

One of the commonly used classifications for fibular hemimelia is that of Achterman and Kalamachi et al. ³ which divides the condition into two types:

• type I: minimal hypoplasia of the fibula

• type II: complete absence of the fibula

Radiographic features

Plain radiograph

• absence of the fibula: needs to be seen on both frontal and lateral radiographs as the fibula may be masked by the tibia in one view

• shortening of the femur

• lateral ray malformations

Ultrasound

• unilateral short lower limb

• non-visualization of two bones in the leg region

• an associated short femur may be seen in cases of proximal femoral focal deficiency

• talipes equinovalgus deformity of the affected foot

• syndactyly involving lateral toes: usually the 4^th and 5^th toes

CT

• absence of the fibula

• absence or malformations of the lateral ray

• there may be syndactyly and polydactyly

• a 3D study is required for the assessment of limb length discrepancies and planning of surgical management

MRI

• demonstrates the same features as plain radiographs and CT

• additional pseudoarthrosis of the femur may be assessed in cases of proximal femoral focal deficiency

• assessment of muscle bulk and agenesis

Treatment and prognosis

The management is mainly surgical and includes limb-lengthening procedures such as Ilizarov's technique or amputation with a prosthesis. Residual deformity and disability is common.