Calibration of a Camera-Based Guidance Solution for Orthopedic and Trauma Surgery

In orthopedic and trauma surgery, fracture reduction usually requires the use of metallic plates and their fixation by means of screws. The employment of guidance solutions during surgical procedures has become of great importance during the last decades. Our guidance solution exploits a small video camera placed directly on the instrument, for example a drill, and a set of small markers placed around the location where the drilling needs to be performed. A calibration step is required in order to determine the relative position of the instrument tip and axis w.r.t the coordinate system of the video camera. In this paper we describe a calibration method for our guidance solution. This calibration method exploits optical markers and a calibration plate whose geometry is known. Moreover, we show how we can exploit directly the image acquired by the video camera during the calibration in order to define an error measure to estimate the accuracy of the calibration. With this method, we achieved respectively an accuracy of 0.23 mm and 3.40 ◦ in the estimation of the instrument tip position and of the orientation of the instrument axis.