Evaluation of a registration technique for intraoperative tracking of the spine

This study evaluates a registration technique for intraoperative tracking o f the spine which consists in matching intraoperative measurements with spe cific surfaces defined on a 3-D preoperative model. The validation study wa s undertaken on a cadaveric spine. The accuracy for four approaches combini ng different tracking systems and 3-D reconstruction techniques were compar ed. The accuracy resulting from the combination of a radiographic 3-D recon struction :md a magnetic digitizer was 5.9+/-2.7mm. The corresponding error s on vertebral rotations were 4.4+/-3.3 degrees, 6.7+/-5.8 degrees and 5.0/-3.8 degrees in frontal, sagittal and transverse planes, respectively. Thi s approach is minimally invasive (only 2 X-rays) and may provide sufficient accuracy for certain clinical applications. With CT scan 3-D reconstructio n, the accuracy was increased by about 2mm, but the high radiation exposure associated with CT scan imaging for long spinal segments makes it unfavora ble to most clinical use. As for the mechanical arm, considering the small increase in accuracy and its awkwardness, its use during surgery is not sug gested.