Introduction
With the use of high resolution ultrasound, there has been an increased awareness of exceptional, but detectable skeletal malformation syndromes. Nevertheless a correct diagnosis is essential for genetic counseling, for pediatric orthopedic counseling and management of the pregnancy ^1-2. Recently, congenital absence of fibula condition was detected by high resolution ultrasound at 24 weeks in a fetus without family history.

Case report:
A 25-year-old patient, gravida 1, para 0, with no notable medical history, was referred to the department at 25 weeks of gestation for a fetal unilateral lower limb malformation. The pregnancy was otherwise uncomplicated and the mother did not take any medication and there were no previous maternal infectious diseases. Ultrasound examination at her first visit at 12 weeks, revealed a single viable fetus with a normal amount of amniotic fluid and nuchal translucency. Ultrasound examination at 24 weeks revealed a single viable fetus with measurements consistent with gestational age. Amniotic fluid was normal. Abnormalities, all located on the right lower limb, included unilateral agenesis of the fibula, hypoplastic tibia and unilateral club-foot with three metatarsa bones (Figure N°1-3).

The thumbs appeared to be normal as the reminder of the anatomic survey was normal. After the parents were informed by a pediatric orthopedic surgeon about the risks and the future handicaps for the neonate, they decided to continue the pregnancy. The fetal karyotype was normal. The baby was born at 38 weeks. Neonatal examination revealed a short right lower extremity (Figure N°4).

The left foot, the arms and the fingers were normal. Neonatal X-rays of the skeletons radiographs confirmed unilateral absence of the fibula (Figure N°5). The right feet was clubbed and there was two toes and two metatarsal bones. The therapeutic project is the amputation of the right leg.

Figure N°5 :
Skeletal radiograph at one day of age confirming unilateral fibula hypoplasia. The malformation of the foot and the tibial anomalie are clearly seen in front of view (a) and lateral view (b).

Discussion:
Fibular hemimelia is a congenital deficiency or absence of the fibula. There is a spectrum of disease from mild fibular hypoplasia to fibular aplasia. The ipsilateral tibia may be hypoplastic, bowed or normal ^3-4.Fibular hemimelia can be frequently associated with proximal focal femoral deficiency, deficiencies of the lateral aspect of the foot, or is part of a malformation syndrome ⁴. The syndrome caused by congenital absence of the fibula has another number of frequently associated pathologic abnormalities, which are illustrated by the case reported.
The syndrome "congenital absence of fibula" is also called: 

• Femur-fibula-ulna syndrome 
• Intercalary hemimelia of the fibula
• Fibula, congenital deficiency of proximal femoral focal deficiency 
• Congenital short tibia with absent or dysplastic fibula ⁵.

Usually sporadic (the recurrence risk for the patient’s siblings is negligible), although a familial incidence (autosomal recessive) has been reported in a small percentage of cases ^6-7.Embryologic studies indicate a development insult to the embryo at about the fifth or sixth week of intrauterine life.Fibula abnormalities vary from a partial absence, with relatively normal-appearing limbs, to absent fibula, with marked shortening of the femur, curved tibia and serious foot anomalies.

Generally three types of congenital absence of fibula have been recognized.

TYPE I: Includes cases with unilateral or partial absence of the fibula, with mild or no bowing of the tibia (10 % of the cases). The leg may or may not be shortened.

Fibular agenesis/hypoplasia is the most common reduction malformation affecting the long bones. Nevetheless agenesis of both the fibulae, however, is rare. The degree of fibular deficiency ranges from unilaterally short to bilaterally absent. A case of occurrence in four consecutive pregnancies has been reported once ¹⁴.

Differential diagnoses are easily eliminated as amniotic band syndrome, campomelic dysplasia, mesomelic dysplasia and other skeletal dysplasias with asymmetrical involvement of the lower limbs as Femoral-facies syndrome (FFS). Fetal thalidomide syndrome must be eliminated too¹⁵.

Nevertheless the differentiation of two forms is more difficult with these one :Femur-fibula-ulna complex (FFU) is not concidered because generally there is asymetrical femoral hypoplasia and hypoplasia of both tibiae and malformation of the hand¹⁶.

Sporadic non-lethal skeletal dysostosis, the spectrum of malformations is hightly variable, with no disorder being common to all patients.

Tibial hemimelia syndrome (THS) encompasses several types of syndrome, all of them involving tibial agenesis or hypoplasia and polydactyly¹⁷. Variable expressions of these clinical findings have been described. THS is associated with bilateral tibial agenesis, clubbing and polysyndactyly of the feet and five triphalangeal finger hands. Unlike bilateral hemimelia syndrome, a rare autosomal dominant condition, unilateral tibial hypoplasia is rarely described.The present case emphasizes the importance of establishing a correct antenatal diagnosis as an essential basis for genetic counseling essentially for subsequent pregnancies and treatment.

Prognosis is good with regard to mental development and life span.  So the prognosis is mainly dependant on the severity of the limb malformation and the possibility of orthopedic surgery¹⁶. Rehabilitation varies depending on the severity of the limb deficiency. Standard obstetrical management is not altered. Fibular deficiency is usually benign, but leg length inequality may be corrected by epiphysiodesis, leg lengthening, ankle
reconstruction using the Gruca technique¹⁸ or simply a shoe raise. Postsurgical therapy on the involved extremity should take into account the patient"s lack of joint motion within the tarsal region. With this in mind, special shoes or accommodative insoles, alone or in combination, should be prescribed in order to facilitate an increase in weightbearing activity with minimal discomfort. Rarely when the foot is nonfunctional, amputation may be considered¹⁹.

The treatment aimed simply to equalise leg length in Type I deficiency, while amputation of the foot and the fitting of a prosthesis were necessary in Type II to obtain satisfactory function²⁰. In France, termination of pregnancy for medical reasons are accepted if gestation is potentially dangerous for the mother or when fetal malformations are lethal and or incurable. In our case, the pediatric orthopedic surgeons confirmed that the limb defect could not totally cured, leaving the child with a permanent limp even after several operations. The parents were offered an opportunity to meet a young boy treated for the same conditions and they opted for continuation of pregnancy.

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