Congenital Limb Abnormalities

Congenital limb amputations and deficiencies are missing or incomplete limbs at birth. The overall prevalence is 7.9/10,000 live births. Most are due to primary intrauterine growth inhibition, or disruptions secondary to intrauterine destruction of normal embryonic tissues. The upper extremities are more commonly affected.

Congenital limb deficiencies have many causes and often occur as a component of various congenital syndromes. Teratogenic agents (eg, thalidomide, vitamin A) are known causes of hypoplastic/absent limbs. The most common cause of congenital limb amputations are soft-tissue and/or vascular disruption defects, such as amniotic band-related limb deficiency, in which loose strands of amnion entangle or fuse with fetal tissue.

Limb deficiencies can be

Longitudinal deficiencies involve specific maldevelopments (eg, complete or partial absence of the radius, fibula, or tibia). Radial ray deficiency is the most common upper-limb deficiency, and hypoplasia of the fibula is the most common lower-limb deficiency. About two thirds of cases are associated with other congenital disorders, including Adams-Oliver syndrome (aplasia cutis congenita with partial aplasia of the skull bones and terminal transverse limb malformations), Holt-Oram syndrome, TAR (thrombocytopenia-absent radius) syndrome, Fanconi anemia, and VACTERL (vertebral anomalies, anal atresia, cardiac malformations, tracheoesophageal fistula, renal anomalies and radial aplasia, and limb anomalies) syndrome.

In transverse deficiencies, all elements beyond a certain level are absent, and the limb resembles an amputation stump. Amniotic bands are the most common cause; the degree of deficiency varies based on the location of the band, and typically, there are no other defects or anomalies. The remaining cases are mostly due to underlying genetic syndromes such as Adams-Oliver syndrome or chromosomal abnormalities.

With transverse or longitudinal deficiency, depending on the etiology, infants may also have hypoplastic or bifid bones, synostoses, duplications, dislocations, or other bony defects; for example, in proximal femoral focal deficiency, the proximal femur and acetabulum do not develop. One or more limbs may be affected, and the type of defect may be different in each limb. Central nervous system abnormalities are rare.

Polydactyly is supernumerary digits and is the most frequent congenital limb deformity. This deformity is classified as preaxial, central, and postaxial.

Preaxial polydactyly is an extra thumb or great toe. The manifestations range from a broad or duplicated distal phalange to complete duplication of the digit. It may occur in isolation, possibly with autosomal dominant inheritance, or it may be part of certain genetic syndromes, including acrocallosal syndrome (with developmental delay and corpus callosum defects), Carpenter and Pfeiffer syndromes (with craniosynostosis Craniosynostosis Craniosynostosis is premature fusion of one or more calvarial sutures. (See also Introduction to Congenital Craniofacial and Musculoskeletal Disorders and Overview of Congenital Craniofacial... read more ), Fanconi and Diamond-Blackfan anemias, and Holt-Oram syndrome (with congenital heart defects Overview of Congenital Cardiovascular Anomalies Congenital heart disease is the most common congenital anomaly, occurring in almost 1% of live births ( 1). Among birth defects, congenital heart disease is the leading cause of infant mortality... read more ).

Central polydactyly is rare and involves duplication of the ring, middle, index fingers. It can be associated with syndactyly and cleft hand. The majority of cases are syndromic.

Postaxial polydactyly is most common and involves an extra digit on the ulnar/fibular side of the limb. Most commonly, the extra finger is rudimentary, but it can be completely developed. In people of African descent, this type of polydactyly is usually an isolated defect. In other populations, it is more often associated with a syndrome of multiple congenital anomalies or chromosomal defects. Among the syndromes to be considered are Greig cephalopolysyndactyly syndrome, Meckel syndrome, Ellis-van Creveld syndrome, McKusick-Kaufman syndrome, Down syndrome Down Syndrome (Trisomy 21) Down syndrome is an abnormality of chromosome 21 that can cause intellectual disability, microcephaly, short stature, and characteristic facies. Diagnosis is suggested by physical anomalies... read more , and Bardet-Biedl syndrome.

Syndactyly is webbing or fusion of fingers or toes. Several different types are defined, and the majority follow an autosomal dominant inheritance pattern. Simple syndactyly involves only fusion of the soft tissue, whereas complex syndactyly also involves fusion of the bones. Complex syndactyly is present in Apert syndrome (with craniosynostosis Craniosynostosis Craniosynostosis is premature fusion of one or more calvarial sutures. (See also Introduction to Congenital Craniofacial and Musculoskeletal Disorders and Overview of Congenital Craniofacial... read more ). Syndactyly of the ring and the small fingers is common in oculo-dento-digital dysplasia. Smith-Lemli-Opitz syndrome manifests with syndactyly of the second and third toes along with multiple other congenital anomalies.