Intermediate ray deficiency--a new type of lower limb hypoplasia

Diagnosis of fibular hemimelia is based on the identification of absence or shortening of the fibula in relation to the tibia. Despite the existence of different classifications of this congenital deficiency, certain morphological forms defy proper classification. One such form is absence of foot rays with leg shortening in the presence of an entire fibula. In these cases, foot morphology suggests that central foot rays, not lateral ones, are affected by the deficiency; thus justifying the hypothesis concerning the existence of a separate type of hypoplasia, which may be named "intermediate ray deficiency" (IRD).

Nine patients with IRD, with an average age of 9.4 years at diagnosis (2.9-15), were analyzed. Clinical and radiographic parameters of the leg and foot were recorded according to the Stanitski classification of fibular hemimelia. The position of the lateral and medial malleoli was assessed. Axial alignment was analyzed according to the Paley method.

The number of foot rays in eight cases was 4, while in one case, it was 3. Talocalcaneal synostosis was observed in seven cases. The shape of the ankle joint was spherical in six cases, horizontal in two cases and valgus in one case. The position of the lateral malleolus was slightly higher compared to normal. An average functional leg length discrepancy was 4.4 cm. The average percentage of fibular shortening was 9.5 %, tibial shortening 8.7 % and femoral shortening 3.3 %. In all of the cases, slight knee valgus was observed on the femoral level (average 3.3°) and tibial level (average 2.0°). As a result, criteria for IRD diagnosis were proposed.

"Intermediate ray deficiency" might be defined as a separate type of lower limb hypoplasia.