Intraoperative Kontrolle der Pedikelschraubenposition mittels 3‐D‐Bildwandler. Eine prospektive Studie bei der Versorgung thorakolumbaler Frakturen

Abstract

Screw misplacement affects the stability of the internal fixateur and may cause neurovascular complications. However, only a computer tomographic scan can show the exact position of the screws. This study was undertaken to assess the reliability of intraoperative three-dimensional imaging (3-D) to view screw positions. The prospective study involved 34 patients with thoracolumbar spine fractures between June 2006 until July 2007 who underwent an intraoperative 3-D-imaging scan after pedicle screw placement. The positions of 136 screws were classified according to the axial view of the 3-D scan into 6 categories. Pedicle and corpus perforation of the screws were measured in 2-mm steps. The quality of the 3-D scan was classified into 3 groups. We compared the results with the screw positions in postoperative CT scans. The computer tomography showed 122 screws in correct positions. 14 screws were misplaced. The average time of the 3-D procedure was 9.6 minutes. In axial C-arm reconstructions, 121 correct positions and 11 malpositions were classified correctly. With regard to the used classification a sensitivity of 3-D-imaging for all screws was 90.0 % and specificity was 97.6 %. The screw position was classified correctly by intraoperative scan in 97.1 % (132/136). 3 of 4 malclassified screws were in the thoracic spine segment (T 1-T 10). Absolute conformity between computer tomography and 3-D imaging classification was reached when the scan quality was good. The quality of 3-D imaging correlated significantly with pedicle diameter (p = 0.004), BMI of the patients (p = 0.001) and the spine level (p = 0.001). Wide pedicles, spine level T 11-L 5 and a low BMI lead to a good quality of scans. Intraoperative imaging by 3-D fluoroscopy can predict very exactly the position of pedicle screws, especially, when a good scan quality is available and the spine section viewed is T 11-L 5. The scan offers the advantage of immediate correction of screw malposition. Thus, computer tomography to control pedicle screw position is dispensable.