An anomalous radiographic appearance of the developing pelvis, in which the greater ischiadic noth (incisura ischiadica major) is shallow and the pelvis takes on the appearance said to resemble a halberd (a weapon especially of the 15th and 16th centuries consisting typically of a battle-ax and pike mounted on a handle). [ https://orcid.org/0000-0002-0736-9199 http://www.ncbi.nlm.nih.gov/pubmed/19232556 ]