IntroductionThe treatment of most spinal diseases is a difficult task because of the rate of immediate, mid-and long-term complications and failures [16]. Surgical planning and clinical follow up often rely on postural and/or dynamic X-ray exams, among other imaging options.Many authors investigated the radiological parameters liable to rule patient's evolution, such as postural and balance parameters [2,4,8,9,11,12,26]. These parameters might be classified in pelvic parameters, either morphologic (incidence) or positional (sacral slope [4,11,12], pelvic angle [8,9]), and spinal parameters (such as lordosis, kyphosis [4,11,12] or plumblines [8,9]). Their measurement is tedious and time consuming while the accuracy of the results may be highly variable depending on the method employed. Furthermore, when trying to compare the results between studies, a major difficulty comes from the differences in the definition, identification and measurement of parameters.Recent computer-based tools allowed for a rapid progress in quantitative measurements of a large range of parameters [9,17,19,20,23,26]. Moreover, these tools allow easy standardisation of X-ray films measurements, which is of paramount importance when comparing studies in multicentric analysis. However, validation of these tools is essential [3,17,18].In 1999, the team of LBM and LIO developed an Xray films analysis software (SpineView 1.0) allowing for the measurement of the main lumbar dynamic and sagittal postural parameters of the spine. The evaluation of this first software was achieved by comparison with direct measurements on plain X-ray films [17,18], and showed good reliability of the measurements. Abstract The objective of this study was to evaluate an X-ray films analysis software, i.e. to estimate the reliability and validity of clinical measurements by means of this software. The authors first performed tests of precision and reproducibility of measures. The precision for dynamic modules was estimated at ±2°for the lumbar analysis and ±3°for the cervical one. Mean reproducibility coefficients calculated for postural modules are about 4°for the angular parameters and 3 mm for the linear ones. We also evaluated clinical applicability of the software through its validity. Reference values calculated on a population of healthy subjects showed agreement with the literature. Then, when analysing postural X-ray films of severe scoliotic patients, we found that inter-observer reproducibility coefficients show a lower reliability of measurements; the main cause seems to be the low visibility of anatomic landmarks due to the quality of X-ray films and to the degree of deformity. This study allowed to better estimate the reliability and the usefulness of this tool, allowing for multicentric studies and exchanges.Keywords Spine AE X-ray AE Quantitative analysis AE Software AE Motion AE Balance Eur Spine J (2006) 15: 982-991