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Titel på arbejdetRadiographic parameters in Adult Spinal Deformity – Reproducibility and prediction of failure
NavnTanvir Johanning Bari
Afdeling / StedRygsektionen, Ortopædkirurgisk afd., Rigshospitalet
UniversitetKøbenhavns Universitet
  • Spine Surgery
Abstract / Summary

Adult Spinal Deformity (ASD) is a common disorder which substantially impacts health-related quality of life and is associated to considerable pain. Although the reason for ASD can be manifold, iatrogenic causes and degenerative aging processes are the most common. Recent decades have seen accelerated technological and surgical advances, and in addition to a demographic shift of the global population, ASD is attracting growing interest. Non-surgical treatment is often chosen as first-line of treatment; although, the outcome of surgery is considerably favorable. Despite compelling effect on every-day living and pain, surgical treatment is associated with a considerable risk of complications, including mechanical failure requiring revision surgery. Radiographic parameters on whole-spine imaging have been established as a crucial cornerstone in diagnosis, assessment of severity, pre-operative planning, and post-operative evaluation of patients with this disorder. In addition, numerous classification and scoring systems are emerging in attempts to identify at-risk patients and predict complications requiring revision surgery.
The overall aim of this thesis was to further scientific knowledge of radiographic parameters in patients with ASD, in efforts to ultimately reduce the surgery-related risks. The Roussouly Classification system was developed to describe the variation in sagittal spine shapes in the normal population, and to serve as templates for the surgical targets. In Study I, this system was assessed for its reproducibility when classified by multiple raters and with repeated measurements. A blinded test-re-test study was performed in 64 patients referred for ASD assessment. Using Fleiss Kappa, inter-rater reliability was estimated as “moderate” and intra-rater reliability as “substantial”, which we found comparable with previous similar estimates of the most commonly used ASD classification system—the SRS-Schwab ASD Classification.
Although, single radiographic parameters of the sagittal spine are frequently used in ASD evaluation, the measurement error has not been established. It is assumed to be approximately ±5°; although, the evidence for this is not well founded. In Study II, we aimed to address this lack in knowledge. In a similar reproducibility study, we estimated the measurement error of four commonly used radiographic parameters. Despite excellent reliability, we found that the measurement error was considerably greater than previously assumed, and that the magnitude of measurement error varied considerably between the included parameters.
Finally, the Global Alignment and Proportion (GAP) score was recently presented with excellent predictability of mechanical failure after ASD surgery. In Study III, we aimed to validate this novel score in a consecutive cohort of 149 patients with minimum 2-years follow-up. Despite only minor dissimilarities to the cohort in the original study, we found no statistical association between the GAP score and mechanical complications after surgery for ASD.
In conclusion, we found moderate to substantial reliability of the Roussouly Classification system; estimated the measurement error of sagittal radiographic parameters to be greater than previously assumed; and were not able to validate the accuracy of the GAP score, all in patients with ASD.

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