Influence of primary and revision spinal fusion surgery on spinopelvic parameters and global sagittal profile.

Although tremendously better insights in the static 2D characteristics of spinal alignment have been achieved the last decade, these are not the main driver of self-perceived HRQOL in Adult Spinal Deformity (ASD) patients. The current state-of-the-art diagnostic algorithm of patient profiling, which is based on 2D spinopelvic alignment analysis and demographic data, fails therefore to analyze the true impact of a spinal deformity on the adult patient. The WHO’s International Classification of Function, disability and health model (ICF-model) offers a comprehensive and structural way to approach a diagnostic algorithm and to unravel the true impact of a chronic disorder on the individual patient. This doctoral thesis demonstrates, with respect to the ICF model, that better insights in the unique functional fingerprint and 3D body structure of the ASD patient offers potential to identify the true drivers of self-perceived HRQOL in the individual patient.

We demonstrated in chapter 1 that individuals with a primary spinal deformity encounter impaired balance control during regular activities of daily life. Furthermore, we investigated the relation between functional impairment and decreased self-perceived HRQOL in ASD patients. To quantify function, we used easy approachable quantitative functional assessments of balance control, like the Balance Evaluation Systems Test (BESTest) and Trunk Control Measurement Scale (TCMS), and investigated whether these clinical tests could complement the current golden standard 2D static spinopelvic alignment analysis and demographics in terms of understanding ASD’s impact on health-related quality of life. We demonstrated that the BESTest has a higher potential to predict HRQOL in the primary ASD population than demographic variables and 2D radiographic spinopelvic measurements. As such, the future introduction of this test during the diagnostic algorithm of patient profiling provides a clear opportunity to unmask functional impairments which are related to HRQOL and unvisible on static X-ray images. Future research should examen whether the BESTest offers potential starting points for novel treatment algoritms including targeted physiotherapy and rehabilitation programs for the ASD patient in a non-surgical, pre-and postoperative setting. 

To understand the impact of a deformed body structure on an individual with respect to the functional dimension of the ICF model, we examined the relation between function and spinal alignment in chapter 2. Function is quantified with performance on Balance Evaluation Systems Test (BESTest). Spinal alignment is quantified by standard 2D and novel Gravity-Line instrumented 3D (i3D) spinal alignment parameters. Therefore, we described the Transverse Gravitational Deviation Index (TGDI) as a novel spinal alignment parameter which aims to describe the threedimensional spinal deformity in the transverse plane with respect to the gravity line. We demonstrated that an increase in the value of sagittal spinopelvic parameters like T1 Pelvic Angle (TPA) and Global Sagittal Axis (GSA), which quantify the global sagittal spinal malalignment despite the use of compensation mechanisms in pelvis and lower limbs, is related to a decreased performance on BESTest. Furthermore, we demonstrated a significant relation between the TGDI and balance control. Indeed, we reported that adult patients with a spinal deformity resulting in a combined coronal and sagittal malalignment at the level of the L3 vertebra, associated with and quantified by an increasing distance between L3 and the gravity line in the transverse plane, are more likely to suffer from impaired balance performance. Although the clinical relevance should be elucidated in future research which combine transverse plane measurements like Axial Intervertebral Rotation and TGDI, this work suggests that patients with occurrence of rotatory subluxation on the level L3 on L4 and progressive lumbar scoliosis, are more likely to encounter declined balance control and thus lower health-related quality of life. In addition, we demonstrated that age is an important driver of balance control in patients with ASD. While these patients get older, they are more at risk for progressive degenerative structural spinal alignment changes and impaired balance performance which puts them in a downward spiral of disability.

In chapter 3, we demonstrated the complementary value of sagittal spinopelvic parameters, TGDI, BESTest and instrumented 3D motion analysis in the diagnostic algorithm. We reported the relation between activity level and self-perceived HRQOL, throughout different types of spinal deformity stratified according to the presence of SRS-Schwab sagittal modifiers. Integrated three-dimensional (3D) motion analysis (iMAS) offers potential to increase insights in the functional fingerprint of our ASD patient by means of kinematic, kinetic and electromyographic data of trunk and lower limbs during walking and other activities in daily life. We demonstrated that besides impaired balance performance on BESTest also a rigid trunk strategy during walking is related to self-perceived HRQOL in adult patients with spinal deformity after correction for covariates. Furthermore, we demonstrated different motion strategies in terms of trunk inclination and pelvic anteversion during walking in comparison to stance throughout different types of spinal alignment with use of sagittal kinematic data of trunk and pelvis. In addition, we attempted to explain these differences in motion strategy during walking with use of Dubousset’s cone of economy in a figurative sense.

In conclusion, this doctoral thesis demonstrates the added value of including new biomechanical measurements in the current diagnostic algorithm of adult patients with a spinal deformity to identify the true drivers of self-perceived HRQOL in the individual patient, with respect to the WHO’s International Classification of Function, disability and health (ICF-model).