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by the American Institute of Ultrasound in Medicine J Ultrasound Med 21:811-815 • 0278-4297
Antenatal Sonographic Diagnosis of Isolated Bilateral Fibular HemimeliaDepartments of Maternal-Fetal Medicine (D.E.A., A.H.J.) and Radiology (B.S.H.), Duke University Medical Center, Durham, North Carolina. Address correspondence and reprint requests to David E. Abel, MD, Duke University Medical Center, DUMC 3967, Durham, NC 27710.
Congenital absence of the fibula, also known as fibular hemimelia, encompasses a spectrum of anomalies involving abnormal growth and development of the fibula.1,2 It is the most common long bone deficiency, followed by aplasia of the radius. According to Coventry and Johnson,3 the condition was first described in 1698. Manifestations of this condition range from mild degrees of limb shortening to its most severe form, which includes complete absence of the fibula with accompanying defects in the femur, tibia, and foot. The severity of foot abnormalities appears to correlate with the severity of the fibular deficiency. Only a few reports of prenatally diagnosed fibular hemimelia have been published,4,5 and to our knowledge there are no prior reports of isolated fibular hemimelia diagnosed antenatally on the basis of sonography. We report a case of the antenatal sonographic diagnosis of complete bilateral fibular hemimelia without the presence of other congenital anomalies.
A 21-year-old primigravida was referred for a fetal anatomic survey at 18 weeks' gestation. The presence of knees bilaterally was noted, with a single bone bilaterally below each knee. In both legs, this single bone was bowed anteriorly and appeared to articulate normally with the knee (Fig. 1  ); thus it was thought that this bone likely represented the tibia. The femurs were normal in configuration, and their lengths of 26.6 mm (right) and 27.3 mm (left) were appropriate for gestational age. Tibial lengths of 14.4 mm (right) and 15 mm (left) were below the fifth percentile for gestational age. The biparietal diameter measured 40.9 mm and was normal for gestational age. All other long bones were normal in length and configuration bilaterally. The hands appeared normal with the appropriate number of digits. All other fetal anatomic characteristics were normal. Amniocentesis revealed a normal male karyotype.
Follow-up sonography at 26 weeks' gestation revealed appropriate interval growth. The tibiae again measured below the fifth percentile bilaterally and appeared bowed (Fig. 2A ). The feet appeared abnormal with an aberrant orientation relative to the leg, and only 3 metatarsal rays were shown (Fig. 2B). The remainder of the antepartum course was uncomplicated, and the patient underwent forceps-assisted vaginal delivery of a 2975-g male neonate at 40 weeks' gestation.
Skeletal radiographs performed on the first day of life (Fig. 3 ) confirmed bilateral complete absence of the fibula. Both tibiae appeared shortened and bowed anteriorly, and the feet appeared dysmorphic with absence of the fourth and fifth metatarsal rays bilaterally. No other congenital anomalies were identified. Treatment options were discussed with the family, and the infant was scheduled to undergo a bilateral Syme amputation with prosthetic fitting at 9 months of age.
Hemimelia is defined as a developmental anomaly characterized by absence of all or part of the distal half of a limb. Of the 4 types of hemimelia (fibular, tibial, radial, and ulnar), fibular hemimelia is the most common. Fibular hemimelia is generally associated with a variety of other lower limb abnormalities, including deformities of the foot with absence of 1 or more lateral metatarsal rays, talipes equinovalgus (the heel is elevated and turned outward from the midline), tibial bowing, and femoral shortening. Approximately 10% of cases are mild, consisting of a partial unilateral deficiency.3 Lewin and Opitz6 reviewed 8 series of fibular aplasia or hypoplasia reported in the English orthopedic literature. They noted a slight male preponderance, although the sex distribution was equal in some individual series. In addition, unilateral involvement occurred in two thirds of cases, with the right fibula more often affected than the left. Tibial bowing was more common in unilateral defects, and the tibiae were often straight when there was bilateral fibular involvement. Two cases of fibular hemimelia diagnosed antenatally on the basis of sonography have been reported previously, but in contrast to our case, both were associated with other congenital anomalies.4,5 Sepulveda et al4 noted unilateral complete absence of the fibula along with an angulated ipsilateral tibia, 3 absent metatarsal rays, and an omphalocele. The other leg was completely normal, and the karyotype was normal. Subsequently, Uffelman and colleagues5 reported a case of bilateral complete absence of the fibulae accompanied by bilaterally bowed and shortened tibiae and bilateral clubfeet with 1 foot missing 2 lateral rays. In addition, these skeletal findings were accompanied by omphalocele and mild ventriculomegaly. The fetal karyotype in this case was normal. The etiology of fibular hemimelia is unclear. Most cases represent a sporadic and isolated event. Of the 493 cases reviewed by Lewin and Opitz,6 only 0.8% were associated with nonskeletal malformations, including 2 neural tube defects, 1 cardiac anomaly, and 1 renal anomaly. Most are nonsyndromic without any family history. Disruptions during the critical period of embryonic limb development (5–8 weeks' gestation) can result in a variety of limb deficiencies that may give rise to varying degrees of fibular hypoplasia or aplasia. Vascular dysgenesis, viral infections, trauma, and environmental influences have been suggested as possible causes. Other conditions should be considered when antenatal sonography suggests fibular deficiency. Proximal femoral focal deficiency consists of congenital absence of the proximal end of the femur and is accompanied by fibular deficiency in approximately 50% of cases.7 The antenatal sonographic diagnosis of proximal femoral focal deficiency has been reported in a fetus with a normal karyotype.8 Other sonographic findings in this fetus included absence of an ipsilateral fibula, an anteriorly bowed tibia, absence of 2 toes, a normal contralateral leg, and normal upper limbs. 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. The antenatal sonographic diagnosis of femur-fibula-ulna syndrome has also been reported.9 The fetus in that report was noted to have bilateral involvement of the femur (1 side was completely absent), bilateral complete absence of the fibulae, normally shaped but slightly shortened tibiae, absent toes bilaterally, a unilaterally absent forearm, and missing fingers from the contralateral hand. Involvement of the upper extremity that occurs in the femur-fibula-ulna complex is not seen in fibular hemimelia. Finally, one may see hypoplastic fibulae in camptomelic 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. 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. The goal of treatment of fibular hemimelia includes equalizing limb lengths and achieving a foot capable of weight bearing.7 Thus treatment is primarily based on the degree of limb length inequality and the severity of the foot deformity.10 In minimal hypoplasia of the fibula with a mild limb length discrepancy, often the only necessary treatment is a shoe lift on the involved side to equalize limb lengths.7 Epiphysiodesis (growth plate arrest) on the contralateral normal side is also an option in these mild cases. In moderate limb length inequality, limb lengthening is an option that preserves height and body proportion and avoids surgery on the normal extremity.11 Limb lengthening can be challenging, because it involves contralateral growth arrest, tibial lengthening, and reconstructive foot surgery. It carries the risk of multiple reconstructive procedures and complications that may necessitate amputation. Candidates for limb lengthening must be carefully selected. Requirements include a plantigrade foot with a stable hip, knee, and ankle.2,12 Cases of a severe limb length discrepancy or complete absence of the fibula are very likely to be accompanied by deformities of the foot. The treatment of choice in these cases is amputation with prosthetic fitting in early childhood.7,12 The most common reconstructive procedures that are performed for children with fibular hemimelia are the Syme and Boyd procedures, 2 techniques for ankle disarticulation. The Syme procedure is a disarticulation at the tibiotalar joint, whereas the Boyd procedure amputates all the foot bones except the calcaneus and fuses the calcaneus to the distal tibia.1 In summary, we have reported a case of isolated bilateral complete fibular deficiency diagnosed antenatally on the basis of sonography. This condition may occur in the presence of other congenital anomalies. A comprehensive fetal anatomic survey, including examination of all long bones, is essential. The treatment should be individualized and based on the severity of the deformity. A multidisciplinary approach, including the genetic counselor, perinatologist, and pediatric orthopedist, can help parents understand the implications of this condition and make informed choices regarding surgical correction.
Received February 14, 2002, from the Departments of Maternal-Fetal Medicine (D.E.A., A.H.J.) and Radiology (B.S.H.), Duke University Medical Center, Durham, North Carolina.
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