Limb deficiency disorders are etiologically heterogeneous, occur as an isolated anomaly or as a part of a syndrome, and may be acquired or congenital. The term limb deficiency incorporates both absence and size reduction of 120 human limb bones, with 205 identified limb deficiency disorders.
Congenital deficiency of the tibia (tibial hemimelia, aplasia, or dysplasia) also known as long bone deficiency is a rare and severe lower limb malformation, with an incidence of approximately 1:1,000,000 live births. It is characterized by lack of part or the entire tibia, with relatively intact fibula. Usually the affected leg is rotated externally and the ventral surface of the foot faces the opposite leg. The majority of the reports are sporadic cases; however apparent autosomal dominant and autosomal recessive families with or without ectrodactyly and other associated limb anomalies also have been reported. The phenotype has been classified into four types: type-I (entire tibia absent), type-II (distal tibia not seen), type-III (proximal tibia not seen), and type- IV (tibia-fibular diastases).
Bilateral and/or unilateral tibial aplasia associated with various other skeletal and extraskeletal malformations, such as congenital diplopodia, triphalangeal thumbs and polydactyly, cleft lip/palate, congenital cardiac defect, vaginal agenesis, cardiovascular defects, imperforate anus radioulnar synostosis, and the most common phenotype, ectrodactyly (split hand /foot) have been seen. Treatment of tibial aplasia traditionally consists of amputating the affected limb to facilitate use of artificial limbs. However, treatment varies with individual cases.
Absence of tibia combined with ectrodactyly is a rare malformation with highly variable manifestations. The full-blown syndrome consists of aplasia of tibia and split-hand/split-foot deformity. Distal hypoplasia or bifurcation of femora, hypo- or aplasia of ulna, and minor anomalies such as patellar aplasia, hypoplastic big toes, postaxial and intermediate polydactyly in connection with split-hand deformity, and cup-shaped ears may be additional malformations. The mildest visible manifestation may be hypoplastic big toes; the severest is tetramonodactyly or transverse hemimelia.
The exact molecular etiology of the cleft hand and absent tibia disorder is not determined yet. However, ongoing molecular studies have mapped the susceptibility loci for SHFLD1 at 1q42.2-q43.