Case of the Week # 486

Case of the Week # 486

Javier Cortejoso
 on 01/13/2023
 on Friday, January 13th, 2023
Longitudinal ultrasound images of the lower extremities show abnormal posturing of the lower legs with bowed tibias, absence of the fibulas and clubfoot deformities.

Clinical guidelines recommend documenting the presence or the absence of the fetal extremities during the second trimester of pregnancy. At times both upper and lower extremities may be present, and an obvious fetal malformation may not be apparent until all the long bones are carefully measured and evaluated. This can be challenging when only one limb or part of a limb is affected.

Hemimelia is defined as a developmental anomaly characterized by absence of all or part of the distal half of a limb. Of the four types of hemimelia (fibular, tibial, radial, and ulnar), fibular hemimelia is the most common. In fact, it is the most common long bone deficiency.

Congenital absence of the fibula, also known as fibular hemimelia, encompasses a spectrum of anomalies involving abnormal growth and development of the fibula. Manifestations of this condition range from a mild degree of limb shortening to its most severe form, which includes complete absence of the fibula with accompanying defects in the femur, tibia, and foot. Only a few reports of prenatally diagnosed fibular hemimelia have been published. The incidence has been estimated at approximately 5.7 to 20 cases per million births and is twice as common in males than in females. Fibular hemimelia can affect a single leg (more commonly the right) or be bilateral. It usually occurs sporadically and its risk of recurrence is almost non-existent. There are rare reports of autosomal recessive inheritance. Fibular hemimelia can be associated with several syndromes, hence the benefit of a complete radiographic exploration of the skeleton. Courtens et al. reported a patient and reviewed four previously reported patients as FATCO syndrome, which consists of fibular aplasia, tibial campomelia and oligosyndactyly. Non-syndromic associations are unusual and include heart defects, renal, urogenital, vertebral (spina bifida), thoraco-abdominal schisis, or cerebral malformations (craniosynostosis).

The diagnosis of congenital absence of the fibula is made by the absence of the fibula and the presence of the commonly associated clubfoot deformity. When antenatal sonography shows only a single bone in the distal lower extremity, it may be difficult to determine whether the bone represents the fibula or tibia. If the bone appears to articulate normally with the femur, the bone likely is the tibia. In addition, fibular deficiency is a more likely diagnosis, because hemimelia of the fibula is considerably more common than hemimelia of the tibia. In tibial deficiency, the deformity usually involves both limbs, the toes are duplicated, and the patient may have coexisting anomalies of the hands.

Fibular hemimelia is generally associated with a variety of other lower limb abnormalities, including marked anteromedial bowing of the tibia with a skin dimple at the point of greatest angulation, marked talipes equinovalgus, and absence of one or more lateral rays of the foot. The severity of foot abnormalities appears to correlate with the severity of the fibular deficiency. Additionally, the ipsilateral femur is usually shortened, and abnormalities of the femoral head and neck are present.

The Achterman and Kalamchi classification system, which is more clinically useful than the preceding ones (Frantz and O’Rahilly and Coventry and Johnson classifications), classifies fibular hemimelia based on the degree of fibular deficiency present. If any portion of the fibula is present, the condition is classified as type I and if the fibula is completely absent, the deformity is classified as type II.

Prognosis is good with regard to mental development and life span, although is mainly dependent on the severity of the limb malformation and the need for orthopedic surgery. Rarely when the foot is nonfunctional, amputation may be considered.

The differential diagnosis includes proximal femoral focal deficiency which consists of congenital absence of the proximal end of the femur and is accompanied by fibular deficiency in approximately 50% of cases. Sonographic identification of a markedly shortened and hypoplastic femur distinguishes proximal femoral focal deficiency from fibular hemimelia. Fibular defects may also be seen in the femur-fibula-ulna complex, a type of short limb dwarfism that consists of varying degrees of femoral and fibular deficiency along with a variety of anomalies of the upper arm. Involvement of the upper extremity that occurs in the femur-fibula-ulna complex is not seen in fibular hemimelia. Finally, hypoplastic fibulae can be seen in campomelic dysplasia, a rare and lethal skeletal dysplasia. The primary features that distinguish this condition from fibular hemimelia include severe angulation of both the tibia and femur and a bell-shaped chest and abdomen. It is easy to diagnose campomelic dysplasia prenatally with the associated scapular hypoplasia, which is a pathognomonic sign in the presence of bowed long bones. Other syndromes that present with absent or hypoplastic fibulae include atelosteogenesis type II (de la Chapelle syndrome), du Pan syndrome (fibular aplasia/complex brachydactyly), Fuhrmann syndrome (fibular aplasia or hypoplasia/femoral bowing/poly-, syn-, and oligodactyly), oro-facio-digital syndrome with fibular aplasia, and Seckel syndrome.

Suggested readings:

[1] Abel DE, Hertzberg BS, James AH. Antenatal sonographic diagnosis of isolated bilateral fibular hemimelia. J Ultrasound Med 2002; 21: 811-815.
[2] Achterman C, Kalamchi A. Congenital deficiency of the fibula. J Bone Joint Surg Br 1979; 61: 133-137.
[3] Courtens W, Jespers A, Harrewijn I, et al. Fibular aplasia, tibial campomelia, and oligosyndactyly in a male newborn infant: a case report and review of the literature. Am J Med Genet A 2005; 134: 321-325.
[4] Cuillier F, Cartault F, Lemaire P. “Absence of fibula, type II.”, Publish date 3/2004.
[5] Gupta AK, Berry M, Verma IC. Congenital absence of both fibulae in four siblings. Pediatr Radiol 1994; 24: 220-221.
[6] Monteagudo A, Dong R, Timor-Tritsch IE. Fetal fibular hemimelia: case report and review of the literature. J Ultrasound Med 2006; 25: 533-537.
[7] Parada S. “Congenital absence of fibula.”, Publish date 5/2002.
[8] Sepulveda W, Weiner E, Bridger JE, et al. Prenatal diagnosis of congenital absence of the fibula. J Ultrasound Med 1994; 13: 655-657.
[9] Uffelman J, Woo R, Richards DS. Prenatal diagnosis of bilateral fibular hemimelia. J Ultrasound Med 2000; 19: 341-344.

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