Purpose and background. Static plain radiographs at the end of uncontrolled bending are the current standard of care for measuring translatory slip in back pain patients. Quantitative fluoroscopy systems (QF) that employ standardised bending protocols have been found to improve precision and reduce dose, but comparative data are lacking. We compared 4 QF methods with static radiographs in a control population, calculating ranges, population variation and measurement errors over 6 weeks. Methods. Fifty-four healthy controls (F=22, M=23) received passive recumbent and active weight bearing QF screenings during controlled motion, plus still fluoro imaging in neutral, flexion and extension. The translatory slip of all levels from L2-S1 was determined for each condition using bespoke image tracking codes (Matlab) and pooled to provide means and ranges of variation (+/-1.96SD). The pooled measurement error, or minimal detectable change (MDC. 95. ), reflecting the intra subject repeatability over 6 weeks was calculated. Ranges of translation for each level (L2-S1), for each type of motion were also calculated. Results. Static radiographs at the end of uncontrolled flexion gave the greatest variation and the worst repeatability, while QF recumbent passive and active weight bearing motion with flexion recorded during the motion had ¼ less variation and twice the repeatability. For individual levels, L2-3 had significantly higher flexion ranges in controlled motion than uncontrolled motion, whereas the converse was true at L4-5 (P<0.001). Conclusion. Dynamic QF measurement of flexion translatory slip gives ¼ less population variation and half the measurement error of static radiographs when measured in the same participants. No conflicts of interest. No funding obtained

Background. Dynamic measurement of continuous intervertebral motion in low back pain (LBP) research in-vivo is developing. Lumbar motion parameters with the features of biomarkers are emerging and show promise for advancing understanding of personalised biometrics of LBP. However, measurement of changes over time inevitably involve error, due to subjects' natural variation and/or variation in the measurement process. Thus, intra-subject repeatability of parameters to measure changes over time should be established. Methods. Seven lumbar spine motion parameters, measured using quantitative fluoroscopy (QF), were assessed for intra-subject repeatability: Intervertebral range-of-motion (IV-RoM), laxity, motion sharing inequality (MSI), motion sharing variability (MSV), flexion translation and flexion disc height. Intra-subject reliability (ICC) and minimal detectable change (MDC95) of baseline and 6-week follow-up measurements were obtained for 109 healthy volunteers (54 coronal and 55 sagittal). Results. Reliability was substantial to excellent for repeated measurements of IV-RoM, laxity, flexion translation and disc height during recumbent passive motion (ICC:0.69–0.95) and during active weight-bearing motion (ICC:0.64–0.92). MSI was moderate to excellent across both positions (ICC:0.43–0.91). The reliability of MSV was generally poorer for both positions (0.14–0.65). For all parameters, measurement error exceeded 42%. Conclusion. Recumbent IV-RoM, laxity and disc height demonstrated the best repeatability at 6-weeks suggesting they may be better outcome moderators in clinical studies than other variables. However measurement errors for all parameters were higher than the minimal changes of interest. These results are limited to healthy controls and should be regarded as reference values. Similar studies in CNSLBP patients are required. No conflicts of interest. Sources of Funding: Dr Rebecca Hemming received a Seedcorn Bursary from the Cardiff Institute of Tissue Engineering and Repair (CITER) and Professor Alan Breen received a project grant from the European Chiropractors Union Research Fund (ECURF)