Bilateral tibial hemimelia type 1 (1a and 1b) with T9 and T10 hemivertebrae: a novel association

ABSTRACT CONTEXT: Congenital absence of the tibia is a rare anomaly with an incidence of one per 1,000,000 live births. It is mostly sporadic and can be identified as an isolated disorder or as part of malformation syndromes. CASE REPORT: A male child, born to unaffected and non-consanguineous parents, presented with shortening of the legs and adduction of both feet. Physical examination at six months of age showed head circumference of 44.5 cm (75th percentile), length 60 cm (< 3rd percentile), weight 7,700 g (50th percentile), shortening of the left thigh and both legs with varus foot. There were no craniofacial dysmorphisms or chest, abdominal, genital or upper-extremity anomalies. Psychomotor development was normal. His workup, including renal and cranial ultrasonography, brainstem auditory evoked potential, and ophthalmological and cardiological examinations, was normal. X-rays showed bilateral absence of the tibia with intact fibulae, distally hypoplastic left femur, and normal right femur. In addition, spinal radiographs showed hemivertebrae at T9 and T10. CONCLUSION: This novel association expands the spectrum of tibial hemimelia. Moreover, this observation highlights the usefulness of this inexpensive diagnostic method (X-rays) for characterizing the great clinical and radiological variability of tibial hemimelia.


INTRODUCTION
Tibial hemimelia is a rare anomaly characterized by deficiency of the tibia with a relatively intact fibula.This defect was described by Otto in 1841 and has an incidence of one per 1,000,000 live births. 1 Tibial hemimelia is mostly sporadic and can be identified as an isolated disorder or as part of malformation syndromes. 2Based on the radiographic appearance, four types of tibial hemimelia have been recognized: type 1a, with absent tibia and hypoplastic lower femoral epiphysis; type 1b, with absent tibia but normal lower femoral epiphysis; 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 distal tibiofibular diastasis and normally developed proximal tibia. 3Patients with this longitudinal deficiency of the lower limb have unique clinical findings that vary in severity and are associated with a wide range of congenital anomalies. 4However, according to the International Clearinghouse for Birth Defects Surveillance and Research, congenital amelia (absence of one or both limbs) is frequently associated with intestinal defects, some renal and genital defects, oral clefts, defects of cardiac septa, anencephaly and other types of musculoskeletal defects. 5is report describes an infant with the novel association of bilateral tibial hemimelia type 1 (distally hypoplastic left femur corresponding to type 1a and normal right femur corresponding to type 1b) with hemivertebrae at T9 and T10.

CASE REPORT
A male infant was referred due to shortened legs and adduction of both feet (Figure 1).Renal and cranial ultrasonography, brainstem auditory evoked potentials, and ophthalmological and cardiological examinations were normal.X-rays (Figure 2) showed bilateral absence of the tibia with intact fibulae, distally hypoplastic left femur and normal right femur.In addition, spine radiographs showed hemivertebrae at T9 and T10 (Figure 3).
The karyotype with G bands (> 550 bands) was reported as 46,XY.He was the first child of healthy and non-consanguineous parents who said that he had not been exposed to mutagens or teratogens and that there was no history of affected relatives.
The pregnancy had been monitored from the 10 th week onwards and had not presented any complications.The patient was born in the 38 th week by vaginal delivery with Apgar scores of 9 and 9.
The birth weight was 2,800 g (25 th percentile) and the length was 42 cm (< 3 rd percentile).Physical examination at six months of age showed head circumference of 44.5 cm (75 th percentile), length 60 cm (< 3 rd percentile), weight 7,700 g (50 th percentile), shortening of the left thigh and both legs with bilateral varus foot.There were no craniofacial dysmorphisms or chest, abdominal, genital or upper-extremity anomalies.His psychomotor development was normal.Treatment consisting of disarticulation of the knee joint and use of a prosthesis will be attempted.

DISCUSSION
The patient's bilateral absence of the tibia with intact fibulae and distally hypoplastic left femur plus normal right femur prompted the diagnosis of bilateral tibial hemimelia types 1a and 1b (Figure 1 and 2); in addition, there were hemivertebrae at T9 and T10 (Figure 3).Over the past forty years, several studies have described over one hundred cases of congenital deficiency of the tibia. 1,3,4,6Among these patients, five  had bilateral tibial hemimelia types 1a and 1b; 1,3,4 however, none of them presented the combination of bilateral tibial hemimelia types 1a and 1b with hemivertebrae at T9 and T10.In our review of the literature, using the Medline (http:// www.ncbi.nlm.nih.gov/pubmed/),Scirus (http://www.scirus.com/srsapp/), Embase (http://www.embase.com),Cochrane Library (http://www.thecochranelibrary.com/view/0/index.html), SciELO (http://www.scielo.org)and Lilacs (http:// lilacs.bvsalud.org/en/)databases, we did not find any articles describing this association (Table 1).A few tibial hemimelia cases have been recorded with hemivertebrae in the lower spine. 4 the present case, the finding of mid-spine hemivertebrae (T9 and T10) could be a coincidence of two independent defects.However, if this was just a random occurrence, the probability would be one in a billion (tibial hemimelia frequency 1 = 1/1,000,000 x hemivertebrae frequency 7 = 1/1000).Hence, this small predictive ratio supports the notion that there is a true association between tibial hemimelia and hemivertebrae, no matter what the level is.Tibial hemimelia encompasses a heterogeneous group of disorders that are classified according to radiological and clinical signs. 3,4,6It may occur as an isolated anomaly or may be associated with a variety of skeletal and extraskeletal malformations such as polysyndactyly, club hand, radioulnar synostosis, bifid femur, cleft lip/palate and imperforate anus.Tibial hemimelia may also constitute a part of a malformation complex or syndrome such as the Gollop-Wolfgang complex and tibial agenesis-ectrodactyly, triphalangeal thumbpolysyndactyly, tibial hemimelia/split-hand/split-foot and Langer-Giedion syndromes. 2,8,9In our case, the previous workup with full ultrasonography and X-ray body scan ruled out malformations that had previously been associated with this disorder.

Figure 1 .
Figure 1.Patient showing shortening of the left thigh and both legs with bilateral varus foot.

Figure 2 .
Figure 2. X-ray showing bilateral absence of the tibia with intact fibulae and distally hypoplastic left femur plus normal right femur.

Table 1 .
Review of medical databases using the descriptors corresponding to the main features presented by the patient, conducted on August 16, 2012