Tibial Hemimelia

► [Longitudinal deficiency of the tibia]

Longitudinal defects of the tibia range from mild hypoplasia to complete absence. Based on the radiographic appearance, four types of tibial hemimelia have been recognized (Schoenecker et al. 1989): type 1, characterized by absent tibia and distally hypoplastic femur; type 2, in which the tibia is distally deficient and well developed proximally; type 3, in which the tibia is proximally deficient and well ossified distally; and type 4, characterized by shortening of the distal tibia,with diastasis of the ankle and normally developed proximal tibia.

Bilateral aplasia of the tibia can be an isolated anomaly in otherwise normal individuals (tibial hemimelia, OMIM 275220) (Emami-Ahari and Mahloudji 1974; McKay et al. 1984). However, it occurs most commonly in association with other congenital defects, including proximal femoral focal deficiency, fibular hemimelia (Fig. 5.33a,b), congenital dislocation of the hip, and coxa valga, or as part of broader syndromes.

Distinct malformation spectra are now emerging in which tibial hemimelia occurs in association with split hand/split foot (Richieri-Costa et al. 1987), cleft lip/palate (Richieri-Costa 1987), and Langer-Giedion syndrome (Stevens and Moore 1999; Turleau et al. 1982). In tibial hemimelia with split hand/split foot (cleft hand/tibial hemimelia, OMIM 119100) malformations may include distal hypoplasia or bifurcation of the femurs, hypo- or aplasia of the ulnas, and minor anomalies such as aplasia of the patellae, hy-poplastic big toes, and cup-shaped ears. Its inheri-

tance is most probably autosomal dominant, with reduced penetrance (Sener et al. 1989). Particular interest attaches to the association with Langer-Giedion syndrome (OMIM 150230), which has suggested that a gene involved in limb development is located in the 8q24.1 region. Its deletion might cause tibial hemimelia (Stevens and Moore 1999). Bilateral tibial hypoplasia with polydactyly (OMIM 188770) of hands and feet has also been reported (Eaton and McKusick 1969; Canki 1980). This may be the same trait as the condition referred to as 'tibial absence with polydactyly' (OMIM 188740). Triphalangeal thumb and syndactyly are consistent features in this syndrome. Significant variability of the clinical manifestations has been noted (Kantaputra and Chali-dapong 2000). In acromelic frontonasal dysplasia (OMIM 603671), a rare variant of frontonasal dyspla-sia, the characteristic craniofacial anomalies are associated with central nervous system malformations and limb defects, including tibial hypoplasia/ aplasia, talipes equinovarus, and preaxial polydacty-ly of the feet (Kantaputra and Chalidapong 2000; Toriello et al. 1986; Verloes et al. 1992). The inheritance pattern is possibly autosomal recessive. The frontonasal malformations have some overlap with acrocallosal (OMIM 200990) and Greig (OMIM 175700) syndromes, but are distinguished from them by the significant hypertelorism and bifid nasal tip.

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