Variability over time of preoperative sagittal alignment parameters: Radiographic and clinical considerations

Study Design. Retrospective review. Objective. To evaluate preoperative variability in radiographic sagittal parameters in adult spinal deformity (ASD). Summary of Background Data. In ASD surgical planning, deformity magnitude is determined from preoperative radiographs. There are no studies evaluating the clinical relevance and timing to repeat radiographs during interval clinic visits and timing to repeat radiograph for preoperative planning. Methods. A total of 139 patients with ASD with minimum two preoperative full-body spine x-rays were included. Cervical, thoracic, lumbar, pelvic, and hip/knee sagittal alignment parameters were analyzed using dedicated spine measurement software. Patients were grouped by time intervals between xrays: A: 8 weeks or lesser, B: 10 to 20 weeks, and C: 21 weeks or more. Changes in sagittal parameters were correlated to age and deformity magnitude (T1 pelvic angle or pelvic tilt [PT] >20°). Results. The cohort had mean age 59 years, mean body mass index 27, 30% men, 95 patients with no prior spine surgery, and 44 patients at minimum 9 months since prior spine surgery. There were 25 patients in group A, 38 in B, and 71 in C. All radiographic measures showed good time-based consistency at intervals less than 21 weeks (groups A and B). Group C had significant increases in PT (1.5°) and hip extension (2.1°) (P<0.05). These changes were greater in group C patients with previous surgery (PT 3.7°; P<0.006, hip extension 3.2°; P<0.025). Greater interval changes in parameters were also associated with higher magnitudes of deformity and younger patient ages. Conclusion. All sagittal radiographic parameters were statistically consistent at intervals of less than 21 weeks. In patients with more than 21 weeks between interval x-rays, change in PT was greater than the standard error of measurement for patients with prior surgery or severe deformity. Consideration should be made to obtain new x-rays for patients with ASD when the interval between clinical visits exceeds 5 months.