Reliability of radiographic assessment of growth modulation from anterior vertebral body tethering surgery in pediatric scoliosis

Purpose To assess the reliability of vertebral height and angular measurements for anterior vertebral body tethering (AVBT). Methods Eight observers measured PA radiographs of 15 idiopathic scoliosis patients treated with AVBT, pre-operative and 4-year follow-up. Vertebral wedging, disc wedging, convex vertebral body heights, and concave vertebral body heights of the 3 apical vertebrae were measured. For each observer, there were a total of 90 measurements for vertebral body height and 75 measurements for all wedging types At least 14 days elapsed between first and second round measurements. Results From the pre-operative to the 4-year follow-up time-point, the total wedging angle over the 3 peri-apical levels fell from 30 +/- 7 degrees to 16 +/- 6 degrees (p < 0.001) and the difference between the convex and concave vertebral heights decreased from 9 +/- 4 to 6 +/- 3 mm (p < 0.001). Interobserver agreement for pre-operative vertebral body heights was good [ICC = 0.80; 95% CI (0.74-0.85)]. At 4-year follow-up there was a moderate agreement [ICC = 0.67 (0.59-0.74)]. There was a poor interobserver agreement for pre-operative wedging angle measurements [ICC = 0.41 (0.32-0.52)] and 4-year follow-up [ICC = 0.45 (0.36-0.56)]. The Limits of Agreement with the Mean (LOAM) for pre-op heights was +/- 2.4 mm, similar to the follow-up +/- 2.6 mm. When raters are averaged in random groups of two the agreement limits decrease to +/- 1.8 mm pre-op and +/- 1.6 mm at follow-up. Similarly for wedging angles, LOAM values among the 8 observers of +/- 4.6 degrees pre-op and +/- 4.2 degrees dropped to +/- 2.7 degrees for both pre-op and follow-up when random groups of two raters were averaged together. Intraobserver agreement ranged from good to excellent per individual (ICC = 0.84-0.94) for pre-operative vertebral body heights, but this decreased at 4-year follow-up (ICC = 0.52-0.88). Intraobserver agreement was low overall for wedging (pre-operative ICC = 0.41-0.71; 4-year follow-up ICC = 0.41-0.76). Conclusion Based on 8 individual observers, interobserver agreement ranged from good (pre-operative vertebral body heights) to moderate (4-year follow-up vertebral body heights) to poor (all wedging angles). To improve the reliability of the measurement of wedging angles, we recommend averaging the measurements of at least two observers.