Summary: Spinal realignment by lumbar pedicle subtraction osteotomy (PSO) is utilized in the setting of sagittal malalignment. The alignment following PSO in long fusions can be predicted. However, the effect lumbar PSO has upon unfused thoracic levels in shorter fusions (reciprocal change [RC]) is poorly understood. These reciprocal changes can negatively impact final post‐operative alignment. Older patients, and those with larger pelvic incidence and truncal imbalance are more likely to have unfavorable thoracic RC (increased kyphosis).
Introduction: Large vertebral resections are frequently utilized in the setting of sagittal malalignment. While the effect of such resection can be anticipated in long fusions, their impact on unfused segments (reciprocal changes; RC) is poorly understood. The objective of this study was to evaluate if RC have a positive or negative impact of spino‐pelvic alignment following lumbar PSO in the setting of shorter fusions.
Methods: Consecutive, multicenter retrospective review of 34 adult patients (mean age=54yo; sd=12) who underwent lumbar PSO with upper instrumented vertebra (/ IV) below T10. Radiographic analysis included pre and post assessment of Thoracic Kyphosis (TK), Lumbar Lordosis (LL), Sagittal Vertical Axis (SVA), T1 Spino Pelvic Inclination (T1SPI), Pelvic Tilt (PT), and Pelvic Incidence (PI). Final SVA and PT were analyzsed to determine successful realignment (SVA < 4 cm, PT < 20 deg). RC in the thoracic spine was designated favorable or unfavorable based upon impact on final SVA and PT.
Results: Mean PSO resection was 26° (SD=9°). LL increased from 20° to 49° (p<0.001). SVA improved from 14 to 4cm (p<0.001) and PT improved from 33° to 25° (p<0.001). Mean increase in TK was 13° (p=0.002). TK was unchanged (<5°) in 11 patients. Five patients had a favorable RC and 18 patients had an unfavorable RC. / nfavorable RC was attributed to junctional failure in 6′ 18 patients. Significant differences in the unfavorable RC group compared to the other patients included; age and greater pre‐operative PT, PI, SVA and T1 SPI (Table). There was no difference in preoperative LL or PSO degree of resection between RC groups.
Conclusion: Significant postoperative alignment changes can occur through unfused thoracic spinal segments following lumbar PSO. Unfavorable RC may limit optimal correction (SVA, PT) and can lead to clinical failures. Riskfactors for unfavorable thoracic RC include: older patients, larger pre‐op PI and PT and worse pre‐op T1 spino‐pelvic inclination and are not simply due to junctional failure. Care should be taken with selective lumbar fusion and PSO in older patients and those with unfavorable pre‐op spino‐pelvic parameters.