Relation between spine alignment and scapular position by plain radiograph examination.

ABSTRACT

Background: Both scapular dynamics and static scapular position are important in the treatment of shoulder dysfunction. This study aimed to create an index that can evaluate scapular position on plain radiographs and evaluate the relation between scapular position and posture accurately. Methods: Using four fresh frozen cadavers, we developed a glenoid angle grade based on the degree of overlap between the shadow of the coracoid inflection point and the upper edge of the scapula on frontal plain radiographs grade 1, no overlap; grade 2, overlaps by less than half of the shadow; grade 3, overlaps by more than half. We then performed a retrospective cohort study that included 329 shoulders of 329 patients who underwent spine surgery. Spine alignment parameters (SPAPs), including cervical lordosis (CL), thoracic kyphosis (TK), lumbar lordosis (LL), pelvic incidence, pelvic tilt, sacral slope, and sagittal vertical axis were measured on standing lateral plain radiographs. Glenoid anterior tilt (GAT) and glenoid anteversion angle (GAVA) were calculated on frontal radiographs and three-dimensional computed tomography scans. Correlations between SPAPs and each angle were investigated, and independent influencing factors were sought in multivariate analysis. Individual factors, GAT, GAVA, and SPAPs were compared among the grades. Results: SPAPs associated with GAT were sagittal vertical axis (R = 0.14, P = .011), TK (R = 0.12, P = .026), and LL (R = -0.11, P = .046). Multivariate analysis identified TK and LL as independent influencing factors (TK, P = .001; LL, P = .008). SPAPs associated with GAVA were CL (R = 0.17, P = .002), TK (R = 0.29, P < .001), and LL (R = 0.25, P < .001). Multivariate analysis identified CL, TK, and LL as independent influencing factors (CL, P = .01; TK, P = .03; LL, P = .03). There were 183, 127, and 19 cases categorized as grades 1, 2, and 3. GAT (grade 1, 24.0 ± 7.8; 2, 32.4 ± 7.0; 3, 41.0 ± 7.8), GAVA (1, 29.3 ± 7.6; 2, 33.7 ± 9.5; 3, 31.5 ± 8.3), and TK (1, 30.6 ± 13.6; 2, 35.1 ± 14.2; 3, 43.1 ± 20.4) differed significantly according to grade. Conclusion: We identified factors that influence scapular position and demonstrated that scapular position can be estimated by a grading system using plain radiographs.