[Intraoperative control of pedicle screw position using three-dimensional fluoroscopy. A prospective study in thoracolumbar fractures]

M Beck, K Moritz, P Gierer, G Gradl, C Harms, T Mittlmeier
Zeitschrift Für Orthopädie und Unfallchirurgie 2009, 147 (1): 37-42

AIM: 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.

METHOD: 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.

RESULTS: 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.

CONCLUSION: 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.

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