To study factors causing postoperative change of PI after surgical correction of ASD and to assess the effect of this variability on postoperative PI-LL mismatch.
PI is used as an individual constant to define lumbar lordosis (LL) correction goal (PI-LL < 10). Postoperative changes of PI were shown but with opposite vectors. The impact of the PI variability on the postoperative PI–LL has not been studied.
The medical and radiographic data analyzed for patients who underwent long posterior instrumented spinal fusion. Inclusion criteria are age, ≥ 20 years old; ASD due to degenerative disk disease (DDD) or scoliosis (DS); ≥ 3 levels fused; and 2-year follow-up or revision. Studied parameters are LL (L1–S1), PI, sacral slope (SS), pelvic tilt (PT), and PI-LL. Measurement error and postoperative changes were defined. Statistical analysis includes ANOVA, correlation, regression, and risk assessment by odds ratio; P ≤ 0.05 considered statistically significant.
Eighty patients were included: mean age, 62.4 years-old (SD, 11.1); female, 63.7%; mean body mass index (BMI), 27.1 (SD, 5.6). Distribution of patients by follow-ups includes preoperative 100%; postoperative (1–3 weeks), 100%; 11–13 months. 90%; 22–26 months, 58%; and revision: 24%.
Pre- versus postoperative PI (∆PI) changed both positively and negatively and the absolute value of change|∆PI| exceeded measurement error (P ≤ 0.05) reaching as high as 31°, and progressed with time; R2 dropped from 0.73 to 0.45 (P < 0.001); ∆PI depended on disproportional changes of SS and PT, preoperative PI, and change of LL. Obesity, DS, and absence of sacroiliac fixation increased |∆PI|. The risk of LL insufficient correction (PI–LL > 10°) associated with a |∆PI|> 6°, P = 0.05. Sacroiliac fixation diminished PI variability only during the first postoperative year.
Preoperative variability and postoperative instability of PI diminish the applicability of the PI–LL < 10° goal to plan correction of LL. An alternative method is offered.
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The authors acknowledge David Calabrese, Francisco Rodriguez Fontan and Bradley J Reeves for their contribution into the collection of primary data for the current study in particular, demographic, clinical and radiographic data, and their preparation for statistical analysis.
The authors did not receive support from any organization for the submitted work.
Conflict of interest
The authors have no conflict of interest (financial or non-financial) to declare that are relevant to the content of this article.
The presented study was performed in accordance with the ethical standards of the 1964 Helsinki Declaration and its later amendments. Ethical approval was waived by the local Ethics. Committee, the Colorado Multiple Institutional Review Board (COMIRB), approval #14–1258).
Informed consent for participation and publication of the results were nor required due to retrospective design of the study which used just results of routine medical care investigations.
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Kleck, C.J., Noshchenko, A., Burger, E.L. et al. Postoperative pelvic incidence (PI) change may impact sagittal spinopelvic alignment (SSA) after instrumented surgical correction of adult spine deformity (ASD). Spine Deform 9, 1093–1104 (2021). https://doi.org/10.1007/s43390-020-00283-2
- Spinal deformity correction
- Sagittal spinopelvic alignment
- Postoperative pelvic incidence instability