An unusual form of congenital anterolateral tibial angulation-the delta tibia

We report three infants with a poorly known form of congenital anterolateral angulation of the tibia with distinctive features seen on lateral roentgenograms. In these films the affected tibia appears to be divided into two segments, one proximal and the other distal, which taper as they approach each other at the site of the angulation, and end separately at the apex of the curve with an intervening radiolucent gap in the anterior tibial cortex. The two tibial segments are originally bridged and held firmly in that position by a well-defined triangular osseous structure located in the concavity of the tibial bow. It appears from the three cases reported in this paper and a few comparable cases in the literature that this form of tibial bowing is not prone to fracture followed by pseudoarthrosis and that it tends to improve (and resolve) spontaneously, with a resorption of the intramedullary bony structures at the apex of the curve resulting in the formation of a normal medullary cavity. A limb length discrepancy of varying degree is the main residual change of the anomaly.