Background \n \nBack pain originating from multiple spinal disorders is the leading cause of disability worldwide. Adult spinal deformity (ASD) is a complex three-dimensional entity of multiple anatomical and functional disorders and predisposes to decreased health-related quality of life (HRQoL). With rising life expectancy and a growing elderly population it is predicted that an increasing number of symptomatic ASD patients will need surgical treatment. It is noteworthy that the prevalence of different grades of ASD, impact on HRQoL and patient-reported outcome (PRO) of ASD surgery has not earlier been reported in the Finnish population. \n \nThe aims of this study were to assess the reliability and repeatability of radiographic diagnostic imaging of ASD and to produce a culturally adapted and valid Finnish version of the Scoliosis Research Society (SRS) Questionnaire version 30 for spinal deformities. Thereafter the prevalence of ASD, applicability of a simplified version of the SRS-Schwab ASD classification and the Finnish SRS-30 were evaluated in a symptomatic adult patient cohort with prolonged degenerative spinal disorders. Finally, the long-term outcome, complications, patient satisfaction and predictive factors for poor outcome of ASD surgery, were investigated. \n \nMethods \n \nOver one year, a consecutive cohort of adult patients was recruited to Studies I-III after referral to the Central Hospital of Central Finland spine clinic due to prolonged degenerative spinal disease. 637 patients returned the completed HRQoL questionnaires and digital full spine radiographs were obtained. The radiographs of 49 patients were randomly selected for the reliability assessment, and a repeatability study of sagittal spinopelvic measurements with basic software tools was performed by three raters differing in their experience of image rating. The SRS-30 underwent translation and cross-cultural adaptation into Finnish and was subsequently validated and psychometrically tested among 274 patients. The SRS-Schwab ASD classification was graded and simplified dividing into mild, moderate and marked groups. The division was tested along with the Finnish SRS-30 questionnaire during evaluation of the prevalence and HRQoL of patients with sagittal malalignment among symptomatic adult patients with spinal degenerative disease but no pre-known deformity. The 79 patients in Study IV were operated during 2007-2016 in our clinic. The clinical and radiographic outcome, patient satisfaction, predictive factors for poor outcome and complications were analysed using the diagnostic tools renovated and tested in Studies I-III. \n \nResults \n \nThe intra-and interrater reliability of the sagittal spinopelvic measurements proved reliable and repeatable with intraclass correlation coefficients (ICC) between 0.78-0.99 and standard error of measurement (SEM) of 0.80-6.2° or 2.2-5.8mm. Greater rater experience in performing the radiographic measurements decreases, and greater complexity of the measurement landmarks increases, intra- and inter-rater bias. \n \nThe reproducibility and internal consistency (ICC 0.905, SEM 0.17, Cronbach α 0.885) of the Finnish version of the SRS-30 was good. The SRS-30 had discriminative validity in the pain, self-image and satisfaction with management domains compared with other questionnaires. A statistically significant difference between the moderate and marked deformity groups in the SRS-30 domains of function/activity (p=0.022) and self-image/appearance (p=0.016) was found. \n \nOf the 637 patients in the consecutive cohort, 25% had moderate and 11% marked spinal deformities. The patients with marked deformity were significantly older, more overweight and more physically inactive than the others in the study population. The 3-class categorization of the SRS-Schwab ASD classification determined well the severity of sagittal deformity and concomitant loss of function, activity (p=0.004), and self-image/appearance (p=0.030) measured with the SRS-30, and disability with the ODI (p=0.033). \n \nASD operation decreased disability (ODI) and pain (VAS) significantly (p=0.001). Postoperative improvement in radiographic sagittal parameters was significant and maintained at 4-5 years of follow-up (p≤0.001). The mechanical failure of instrumentation of bone resulted in reoperation risk of 13.9% within the first and 29.8% during the 5-year follow-up. According to SRS-30, 49 (62.0%) patients were satisfied or very satisfied with the treatment and 57 (72.1%) would have the same operation again. Depression predicted poor outcome with an odds ratio of 6.97 (p=0.018). \n \nConclusions \n \nThe study comprised an unselected consecutive cohort of adult patients with prolonged degenerative spinal diseases, and thus the results can be generalized. Rater experience had a positive influence on the otherwise good reliability and repeatability of the spinopelvic measurements taken from full spine radiographs. The deformity-specific Finnish SRS-30 translation proved reliable and valid among the study cohort. The simplified categories of the SRS-Schwab ASD classification can detect different grades of deformity and related loss of HRQoL. Long-term radiographic and patient-reported clinical outcomes after the ASD surgery remained significantly better than preoperative scores. Risk for reoperation was highest during the first postoperative year. However good patient satisfaction and outcomes could be achieved irrespective of adverse effects. Depression was the only significant predictive factor for poor outcome after ASD surgery. \n \n \n \nKeywords: adult spinal deformity, ASD, scoliosis, kyphosis, full-spine radiograph, reliability, repeatability, validation, outcome, health-related quality of life, Scoliosis Research Society questionnaire 30, SRS-30, SRS-Schwab ASD classification, spine surgery, pelvic incidence, pelvic tilt, sagittal vertical axis, lumbar lordosis, thoracic kyphosis