Accuracy and repeatability of the stick marker technique for external measurement of the sacral angle during trunk flexion (IJIE 99-27)

Lateral radiographs were taken of 16 subjects in the upright position through 90 degrees flexion, in 30 degrees increments. The radiographic sacral angle was compared with the angle estimated from the external stick marker technique. Three observers independently and repeatedly examined the sacral angles using these two methods. Results showed that the radiographic and marker techniques yielded significantly different sacral angles, with the latter tending to underestimate the angle. These differences in the measurements of sacral angle will lead to overestimating the compression (with an average 115 N) and to underestimating the shearing force (with a range of 57-268 N) at L5/S1 disc in a biomechanical analysis. The inter-observer reliability of the stick marker measurements were poor for the four trunk positions, however the measurements did show good intra-observer reproducibility. Relevance to industry. Measurements of sacral angle are important in assessing the stresses acting on the low back in lifting. Our findings indicate that the stick marker technique does not yield accurate or reliable estimates of the sacral angle. The result implied that the use of this noninvasive method should be interpreted cautiously. (C) 2000 Elsevier Science B.V. All rights reserved.