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. 2014 Mar;23(3):689-94.
doi: 10.1007/s00586-013-3080-2. Epub 2013 Oct 31.

Development and validation of a quantitative method to assess pedicle screw loosening in posterior spine instrumentation on plain radiographs

Emin Aghayev  1 , Nicolas Zullig, Peter Diel, Daniel Dietrich, Lorin M Benneker
Affiliations

Development and validation of a quantitative method to assess pedicle screw loosening in posterior spine instrumentation on plain radiographs

Emin Aghayev et al. Eur Spine J. 2014 Mar.

Abstract

Purpose: Currently, the diagnosis of pedicle screw (PS) loosening is based on a subjectively assessed halo sign, that is, a radiolucent line around the implant wider than 1 mm in plain radiographs. We aimed at development and validation of a quantitative method to diagnose PS loosening on radiographs.

Methods: Between 11/2004 and 1/2010 36 consecutive patients treated with thoraco-lumbar spine fusion with PS instrumentation without PS loosening were compared with 37 other patients who developed a clinically manifesting PS loosening. Three different angles were measured and compared regarding their capability to discriminate the loosened PS over the postoperative course. The inter-observer invariance was tested and a receiver operating characteristics curve analysis was performed.

Results: The angle measured between the PS axis and the cranial endplate was significantly different between the early and all later postoperative images. The Spearman correlation coefficient for the measurements of two observers at each postoperative time point ranged between 0.89 at 2 weeks to 0.94 at 2 months and 1 year postoperative. The angle change of 1.9° between immediate postoperative and 6-month postoperative was 75% sensitive and 89% specific for the identification of loosened screws (AUC = 0.82).

Discussion: The angle between the PS axis and the cranial endplate showed good ability to change in PS loosening. A change of this angle of at least 2° had a relatively high sensitivity and specificity to diagnose screw loosening.

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Figures

Fig. 1
Fig. 1
Standing lateral radiographs of L1 2 days (a) and 2 months (b) after posterior stabilization L1-S1 and early screw loosening in L1 (65-year-old female patient). For quantitative assessment the angle (ε2) between the cranial endplate (solid line) and the bisector (solid line) of the screw axis (dashed lines) was measured. The angle increased between the two follow-ups from 6.0° to 14.3°
Fig. 2
Fig. 2
ROC curve analysis for the identification of an optimal cut-off value in discrimination between loosened and control screw: a comparing immediate postoperative and 2-month postoperative images, b comparing immediate postoperative and 1-year postoperative images
See this image and copyright information in PMC

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