This description of the physiological spinal sagittal balance should serve as a baseline in the evaluation of pathological conditions associated with abnormal angular parameter values. Before a patient with spinal sagittal imbalance is treated, the reciprocal balance between various spinal angular parameters needs to be taken into account. The correlations between angular parameters may also be useful in calculating the corrections to be obtained during treatment.

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Using a specialized orthopedic software package, the authors investigated the sagittal spinal shape and the position of the pelvis in the space in patients with isthmic spondylolisthesis and in persons with no such symptoms. Digitized lateral spinal radiographs of 30 healthy volunteers and 48 patients were evaluated. The absolute values and significant correlations between parameters were analyzed. The pelvic parameters correlated well with lordosis, which shows sagittal balance in the asymptomatic group. The hyperlordosis and the horizontally positioned sacrum in isthmic spondylolisthesis enlarge the tensile force component of gravity, which may cause the lysis. Finally, the authors developed a new balance between the pelvis and the spine after slipping of the vertebral body. The degree of slipping correlated well with the sacrofemoral anatomic constant (incidence), which is unique in each person.

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Using a special software program we measured spinopelvic parameters on digitised radiographs of the entire spine and the pelvis of 50 patients with lumbar disc herniation and compared these with the same measurements on 30 healthy subjects. In the disc hernia group the patients had a relatively straight spine in the sagittal plane. The sacrum was more vertical, and the value of the lumbar lordosis was lower, as was the amplitude of the spinal curvatures, when compared with those of the healthy group. This results in a higher gravitational compressive force which may, in turn, lead to progressive degeneration of the discs. The anterior shift of the line of gravity may cause spinopelvic instability, and contraction of the posterior spinal muscles in trying to balance this disturbed spatial relationship may produce back pain.Résumé Avec un logiciel spécial nous avons mesuré des paramètres rachidiens et pelviens sur les radiographies numérisées de 50 patients avec hernie discale lombaire et de 30 sujets sains. Dans le groupe avec hernie discale les patients avaient une colonne vertébrale relativement droite dans le plan sagittal. Le sacrum était plus vertical, la lordose lombaire plus discrète et donc l'amplitude des courbures vertébrales plus faible en comparaison du groupe sain. Cela peut mener à la dégénérescence progressive des disques, par suite d'une plus grande force compressive gravitationnelle. La modification de la ligne de gravité antérieure peut causer l'instabilité rachidienne -pelvienne. Les muscles vertébraux postérieurs peuvent avoir tendance à corriger ce déséquilibre spatial ce qui peut causer des douleurs postérieures.

Addressing the heterogeneity of both the outcome of a disease and the treatment response to an intervention is a mandatory pathway for regulatory approval of medicines. In randomized clinical trials (RCTs), confirmatory subgroup analyses focus on the assessment of drugs in predefined subgroups, while exploratory ones allow a posteriori the identification of subsets of patients who respond differently. Within the latter area, subgroup discovery (SD) data mining approach is widely used—particularly in precision medicine—to evaluate treatment effect across different groups of patients from various data sources (be it from clinical trials or real-world data). However, both the limited consideration by standard SD algorithms of recommended criteria to define credible subgroups and the lack of statistical power of the findings after correcting for multiple testing hinder the generation of hypothesis and their acceptance by healthcare authorities and practitioners. In this paper, we present the Q-Finder algorithm that aims to generate statistically credible subgroups to answer clinical questions, such as finding drivers of natural disease progression or treatment response. It combines an exhaustive search with a cascade of filters based on metrics assessing key credibility criteria, including relative risk reduction assessment, adjustment on confounding factors, individual feature’s contribution to the subgroup’s effect, interaction tests for assessing between-subgroup treatment effect interactions and tests adjustment (multiple testing). This allows Q-Finder to directly target and assess subgroups on recommended credibility criteria. The top-k credible subgroups are then selected, while accounting for subgroups’ diversity and, possibly, clinical relevance. Those subgroups are tested on independent data to assess their consistency across databases, while preserving statistical power by limiting the number of tests. To illustrate this algorithm, we applied it on the database of the International Diabetes Management Practice Study (IDMPS) to better understand the drivers of improved glycemic control and rate of episodes of hypoglycemia in type 2 diabetics patients. We compared Q-Finder with state-of-the-art approaches from both Subgroup Identification and Knowledge Discovery in Databases literature. The results demonstrate its ability to identify and support a short list of highly credible and diverse data-driven subgroups for both prognostic and predictive tasks.

Summary: The present study is a numerical comparison using finite-element analysis (FEA) oftwo different concepts of spinal fixation devices when implanted. These implants are 1) the Easy ®, "rigid" Screw/Rod (0 6mm) system; z) the Twinflex ®, "dynamic" system (o 2 x 2.5 mm ELF). A parameterised 3D FEA model of an L3-sacrum segment, developed by Lavaste, Skalli & Robin, was used. Geometric and mechanical models of each implant were then constructed, before being inserted in the spinal segment model. Then, for model validation, these two L3-$2 instrumented segmental models were submitted to similar boundary conditions as used in a previous in vitro comparison of the same implants. Flexion loaddisplacement curves were then controlled using experimental results. Loads acting on screws and longitudinal elements were calculated and analysed for a better understanding of the intrinsic differences between both constructs. Load-displacement responses of both constructs were quite similar (L3 sagittal rotation at lo N.m = -1.5°), while loads in the implant were not. For example, the axial push-in forces at the $1 screws were equal to 3o N for the Twinflex®, and 15o N for the Easy® Screw/Rod system. The pull-out forces at the Sz screws were respectively looN and 20o N for the Twinflex and Screw/Rod Concept. At other levels, axial forces were all lower than 60 N, the Twinflex®, values being higher than the Easy ®ones. Bending moments along screws were respectively o.7 N.m and 1. 4 N.m at the L3 level for the Twinflex ® and the Easy ~ systems. At lower levels, values were all below o.6 N.m, again with a reversed proportion. Bending moments calculated along longitudinal elements were always lower than 0.3 Nm for the Twinflex®, and up to 2 N.m for the Easy® system. Axial forces in the Twinflex ® longitudinal elements were about 16o N, and about lOO N in the Easy ® rods. Although the numerical approach mainly provides tendencies, it clearly seems that reducing flexural stiffness of lumbar fixation induces more homogeneous load transmission along the construct, and greatly reduces axial push-in/pull-out forces at the SdSz levels, and all this without reducing the rigidity of the whole construct. Conversely, it has been shown that "rigid" longitudinal elements may concentrate stresses at the construct extremities, relieving loads at intermediate levels at the same time, which may be the sign of a stress-shielding-like phenomenon. These differences arise from a fundamental difference between both kinds of longitudinal elements in the way they transmit loads. The o 6 mm rods mainly oppose a bending reacfion torque to the applied flexion moment, whereas the Twinflex ® construct mainly balances the applied flexion torque by an anterior compression of the anterior column, combined with posterior traction on its longitudinal elements (ELF).