Orientation of the first metatarsal base wedge osteotomy: perpendicular to the metatarsal versus weight-bearing surface.

Changes have been proposed in the orientation of the first metatarsal base closing abductory wedge osteotomy based on sound theoretical reasoning. The newer proposed method, utilizing an orientation of the osteotomy perpendicular to the weight-bearing surface, produces only pure transverse plane motion and no loss of ground contact by hinge axis mechanisms. In contrast, the traditional orientation of the osteotomy, perpendicular to the long axis of the metatarsal, produces extraneous frontal plane motion that results in loss of ground contact as the osteotomy site is closed. The presented study formulates a mathematical model to calculate the amount of loss of ground contact produced by the traditional osteotomy orientation. The values obtained from 168 calculations suggest far less clinical significance to the change than has been implied or stated previously.