Tibial hemimelia

Tibial hemimelia is also a congenital longitudinal deficiency. The main characteristic is the partial or total absence of the shin bone (tibia).

Tibial hypoplasia: incomplete development of the tibia

Tibial aplasia: complete absence of the tibia

The cause for tibial hemimelia also remains unclear to date. Unlike with fibular hemimelia, this malformation is often hereditary. The hereditary form is frequently accompanied by additional malformations. Therefore, genetic testing is recommended before any future pregnancies.

Classification

Among the different classifications of tibial hemimelia, the one by Kalamchi and Dawe (1985) is easily understandable and simple in everyday use. In addition to the radiological characteristics, functional characteristics (knee flexion contracture and quadriceps function) are also considered.

In actual therapy planning, however, it is often necessary to use a substantially more complex classification system (MRI!).

Classification of congenital tibial aplasia in accordance with Kalamchi and Dawe 1985:

Type
Radiological characteristics
Knee flexion contracture
Quadriceps activity
I
>45°
none
II
25°–45°
reduced
III
none
normal

Type I
Type II
Type III

 

The decision as to which therapeutic procedure is most suitable is based, in particular, on the function of the knee with its extensor system, an existing flexion contracture and knee instability.

Clinical picture

Just as in other longitudinal deficiencies of the extremities, tibial hemimelia is accompanied by other malformations of the leg. Frequently, there are additional deformities of the upper extremities. The foot deformity depends on the severity of the shin defect: usually, the affected foot is severely tilted inward (varus position) and the number of toes varies significantly, while a surplus of toes (polydactyly) is also not uncommon. Since the foot is unsupported due to the tibial hemimelia, the foot is usually unstable and cannot bear weight initially.

Apart from the decrease in length of the affected lower leg, the knee also frequently shows abnormalities. Depending upon the level of severity, the knee is unstable as a result of the malformation and is often fixed in flexion so that initially it is not possible to bear weight here either. If the shin bone is missing completely, then the calf bone is positioned laterally and above the actual knee level.

Unfortunately, with tibial hemimelia, further physical damage cannot be completely ruled out. In the vast majority of cases, however, the pediatric patients are otherwise in good health and show normal mental and physical development.