Development and evaluation of a semi-automatic technique for determining the bilateral symmetry plane of the facial skeleton.

During reconstructive surgery of the face, one side may be used as a template for the other, exploiting assumed bilateral facial symmetry. The best method to calculate this plane, however, is debated. A new semi-automatic technique for calculating the symmetry plane of the facial skeleton is presented here that uses surface models reconstructed from computed tomography image data in conjunction with principal component analysis and an iterative closest point alignment method. This new technique was found to provide more accurate symmetry planes than traditional methods when applied to a set of 7 human craniofacial skeleton specimens, and showed little vulnerability to missing model data, usually deviating less than 1.5° and 2 mm from the intact model symmetry plane when 30 mm radius voids were present. This new technique will be used for subsequent studies measuring symmetry of the facial skeleton for different patient populations.