Aims. The aim of this study was to determine the influence of pelvic parameters on the tendency of patients with adolescent idiopathic scoliosis (AIS) to develop flatback deformity (thoracic hypokyphosis and lumbar hypolordosis) and its effect on quality-of-life outcomes. Patients and Methods. This was a radiological study of 265 patients recruited for Boston bracing between December 2008 and December 2013. Posteroanterior and lateral radiographs were obtained before, immediately after, and two-years after completion of bracing. Measurements of coronal and sagittal Cobb angles, coronal balance, sagittal vertical axis, and pelvic parameters were made. The refined 22-item Scoliosis Research Society (SRS-22r) questionnaire was recorded. Association between independent factors and outcomes of postbracing ≥ 6° kyphotic changes in the thoracic spine and ≥ 6° lordotic changes in the lumbar spine were tested using likelihood ratio chi-squared test and univariable logistic regression. Multivariable logistic regression models were then generated for both outcomes with odds ratios (ORs), and with SRS-22r scores. Results. Reduced T5-12 kyphosis (mean -4.3° (. sd. 8.2); p < 0.001), maximum thoracic kyphosis (mean -4.3° (. sd. 9.3); p < 0.001), and lumbar lordosis (mean -5.6° (. sd. 12.0); p < 0.001) were observed after bracing treatment. Increasing prebrace maximum kyphosis (OR 1.133) and lumbar lordosis (OR 0.92) was associated with postbracing hypokyphotic change. Prebrace sagittal vertical axis (OR 0.975), prebrace sacral slope (OR 1.127), prebrace pelvic tilt (OR 0.940), and change in maximum thoracic kyphosis (OR 0.878) were predictors for lumbar hypolordotic changes. There were no relationships between coronal deformity, thoracic kyphosis, or lumbar lordosis with SRS-22r scores. Conclusion. Brace treatment leads to flatback deformity with thoracic hypokyphosis and lumbar hypolordosis. Changes in the thoracic spine are associated with similar changes in the lumbar spine. Increased sacral slope, reduced pelvic tilt, and pelvic incidence are associated with reduced lordosis in the lumbar spine after bracing. Nevertheless, these sagittal parameter changes do not appear to be associated with worse quality of life. Cite this article: Bone Joint J 2019;101-B:1370–1378

To determine if the use of high density implants (i.e. high proportion of pedicle screws relative to number of spinal levels involved) causes significant loss of thoracic kyphosis and its effect on sagittal balance in adolescent idiopathic scoliosis.

Retrospective analysis of pre and post-operative radiographs to assess sagittal balance and C7-L1 kyphosis angle.

17 patients (16 females, 1 male). All right sided single thoracic curves. All surgery performed by single surgeon (Senior author, ED)

Comparison of pre and post operative sagittal balance and C7-L1 kyphosis angle. Assessment of implant density (i.e. proportion of pedicle screw relative to number of spinal levels involved in correction).

9 patients demonstrated improved sagittal balance following surgery. There was no significant difference (p value 0.83) between the pre and post op C7-L1 kyphosis angle. Mean angle pre op 28.9 (95% CI 20.3 to 37.5). Mean angle post op 29.6 (95% CI 22.2 to 37.0). No correlation identified between sagittal balance correction and kyphosis angle. Metal density ranged from 79-100%.

Although the sample size in this series is modest, high density implants do not significantly affect the kyphosis angle in the operative management of adolescent idiopathic scoliosis in the thoracic spine.

Objective. To determine if there is a differing effect between two spinal implant systems on sagittal balance and thoracic kyphosis in adolescent idiopathic scoliosis. Methods. Retrospective analysis of pre and post-operative radiographs to assess sagittal balance, C7-L1 kyphosis angles and metal implant density. Group 1 (Top loading system): 11 patients (9 females, 2 males) Single surgeon NB. Group 2 (Side loading system): 17 patients (16 females, 1 male) Single surgeon ED. Total 28 patients. All single right sided thoracic curves. Comparison of pre and postoperative sagittal balance and C7-L1 kyphosis angle for each spinal system. Assessment of implant density (i.e. proportion of pedicle screw relative to number of spinal levels involved in correction). Results. 16 patients demonstrated improved sagittal balance following surgery. There was no significant difference between the pre and post op C7-L1 kyphosis angle in either group (p value 0.06 and 0.83 respectively) although a greater discrepancy was noted in Group 1. In group 1, the mean angle pre op was 33.1 (95% CI 27.3 to 38.9) and post op was 26.2 (95% CI 22.5 to 29.9). In Group 2, the mean angle pre op was 28.9 (95% CI 20.3 to 37.5) and post op was 29.6 (95% CI 22.2 to 37.0). No correlation identified between sagittal balance correction and kyphosis angle. Metal density ranged from 60-100%. Conclusions. Although the numbers in this series are modest they do suggest that high density metal implants do not lead to a flatback deformity in the sagittal plane. There is no significant difference in the pre and post op kyphosis angles for either implant system used in this study although the results for Group 1 do approach statistical significance. Larger prospective multicentre studies are required to quantify the true significance of these results. Ethics Approval: Audit/Service Standard in Trust