In vivo measurement of 3-D skeletal kinematics from sequences of biplane radiographs: Application to knee kinematics

Current noninvasive or minimally invasive methods for evaluating in vivo kn ee kinematics are inadequate for accurate determination of dynamic joint fu nction due to limited accuracy and/or insufficient sampling rates. A three- dimensional (3-D) model-based method is presented to estimate skeletal moti on of the knee from high-speed sequences of biplane radiographs, The method implicitly assumes that geometrical features cannot be detected reliably a nd an exact segmentation of bone edges is not always feasible, An existing biplane radiograph system was simulated as two separate single-plane radiog raph systems. Position and orientation of the underlying bone was determine d for each single-plane view by generating projections through a 3-D volume tric model (from computed tomography), and producing an image (digitally re constructed radiograph) similar (based on texture information and rough edg es of bone) to the two-dimensional radiographs, The absolute 3-D pose was d etermined using known imaging geometry of the biplane radiograph system and a 3-D line intersection method. Results were compared to data of known acc uracy, obtained from a previously established bone-implanted marker method. Difference of controlled in vitro tests was on the order of 0.5 mm for tra nslation and 1.4 degrees for rotation. A biplane radiograph sequence of a c anine hindlimb during treadmill walking was used for in vivo testing, with differences on the order of 0.8 mm for translation and 2.5 degrees for rota tion.