Optimal Pelvic Incidence Minus Lumbar Lordosis Mismatch after Long Posterior Instrumentation and Fusion for Adult Degenerative Scoliosis

Objective: To evaluate the influence of Scoliosis Research Society (SRS)-Schwab sagittal modifiers of pelvic incidence minus lumbar lordosis mismatch (PI-LL) on clinical outcomes for adult degenerative scoliosis (ADS) after long posterior instrumentation and fusion. Methods: This was a single-institute, retrospective study. From 2012 to 2014, 44 patients with ADS who underwent posterior instrumentation and fusion treatment were reviewed. Radiological evaluations were investigated by standing whole spine (posteroanterior and lateral views) X-ray and all radiological measurements, including Cobb's angle, LL, PI, and the grading of vertebral rotation, were performed by two experienced surgeons who were blind to the operations. The patients were divided into three groups based on postoperative PI-LL and the classification of the SRSSchwab: 0 grade PI-LL (<10 degrees, n = 13); + grade PI-LL (10 degrees-20 degrees, n = 19); and ++ grade PI-LL (>20 degrees, n = 12). The clinical outcomes were assessed according to Japanese Orthopaedic Association (JOA) score, Oswestry Disability Index (ODI), Visual Analog Scale (VAS), Lumbar Stiffness Disability Index (LSDI), and complications. Other characteristic data of patients were also collected, including intraoperative blood loss, operative time, length of hospital stay, complications, number of fusion levels, and number of decompressions. Results: The mean operative time, blood loss, and hospital stay were 284.5 +/- 30.2 min, 1040.5 +/- 1207.6 mL, and 14.5 +/- 1.9 day. At the last follow-up (2.6 +/- 0.6 years), the radiological and functional parameters, except the grading of vertebral rotation, were all significantly improved in comparison with preoperative results (P < 0.05), but it was obvious that an ideal PI-LL (<= 10 degrees) was not achieved in some patients. Significant differences were only observed among the three groups in the ODI and LSDI. Patients with + grade PI-LL seemed to have the best surgical outcome compared to those with 0 and ++ grade PI-LL, with the lowest ODI score (+ grade vs 0 grade, 17.3 +/- 4.9 vs 26.0 +/- 5.4; + grade vs ++ grade, 17.3 +/- 4.9 vs 32.4 +/- 7.3; P < 0.05) and lower LSDI (+ grade vs 0 grade, 1.6 +/- 1.0 vs 3.5 +/- 0.5, P < 0.05; + grade vs ++ grade, 1.6 +/- 1.0 vs 0.6 +/- 0.5, P > 0.05). A Pearson correlation analysis further demonstrated that LSDI was negatively associated with PI-LL. Furthermore, the incidence rate of postoperative complications was lower in patients with + grade PI-LL (1/19, 5.26%) than that in patients with 0 (2/13, 15.4%) and ++ grade PI-LL (3/12, 25%). Conclusion: Our present study suggest that the ideal PI-LL may be between 10 degrees and 20 degrees in ADS patients after long posterior instrumentation and fusion.