Optimum pelvic incidence minus lumbar lordosis value after operation for patients with adult degenerative scoliosis

Abstract

Background context: Schwab classification for adult degenerative scoliosis (ADS) concluded that health-related quality of life was closely related to curve type and three sagittal modifiers. It was suggested that pelvic incidence minus lumbar lordosis value (PI-LL) should be corrected within -10°~+10°. However, recent studies also indicated that ideal clinical outcomes could also be achieved in patients without the ideal PI-LL mentioned above.

Purpose: This study evaluated the relation between the clinical outcomes and the PI-LL of Chinese patients with ADS who received long posterior internal fixation and fusion.

Study design: This was a single-center retrospective comparative study of patients treated by long posterior internal fixation and fusion in our hospital between 2010 and 2014.

Patient sample: Inclusion criteria were age >45 years at the time of surgery, Cobb angle of lumbar curves ≥10°, long posterior internal fixation and fusion ≥least 3 motion segments, follow-up ≥2 years, complete preoperative and postoperative radiographic data, and functional evaluation results. Exclusion criteria were history of previous lumbar spine surgery, other kinds of scoliosis, history of severe spinal trauma, spinal tumor, ankylosing spondylitis, and spinal tuberculosis. Seventy-four patients were enrolled in this study.

Outcome measures: Operative parameters included intraoperative blood loss, duration of surgery, length of hospital stay, number of fusion levels, and decompression. The radiological measurements included Cobb angle of the curves and PI-LL. Clinical outcomes were evaluated by the Japanese Orthopaedic Association score, Oswestry Disability Index (ODI), visual analog scale, and Lumbar Stiffness Disability Index (LSDI). In addition, the complications of surgery were also collected. One-way analysis of variance, Student t test, Kruskal-Wallis test, Pearson chi-square test, and curve estimation were calculated for variables.

Methods: All the patients were divided into Group 1 (long instrumentation and fusion to L5) and Group 2 (long instrumentation and fusion to S1). Operative parameters, radiological measurements, clinical outcomes, and complications of surgery were compared between two groups to confirm whether distal fusion level could influence therapeutic effect. Then patients were divided into PI-LL<10° (Group A), 10°≤PI-LL≤20° (Group B), PI-LL>20° (Group C). Operative parameters, radiological measurements, clinical outcomes, and complications of surgery were compared between each of the two groups. Curve estimation was performed to evaluate the relationship between postoperative PI-LL and clinical outcomes.

Results: No difference was found between Group 1 and Group 2 in all postoperative parameters (p>.05). There were significant differences in final ODI (p<.001) and final LSDI (p<.001) among Group A, Group B, and Group C. Cubic curve model fitted the relationship between PI-LL and final ODI better than other models (R²=0.379, p<.001). Cubic curve model fitted the relationship between PI-LL and final LSDI better than other models (R²=0.691, p<.001). There was a significant difference in proximal junctional kyphosis (PJK) among groups (p=.038). No significant difference was found in other parameters.

Conclusions: Optimal PI-LL value may be achieved between 10° and 20° in Chinese patients with ADS after long posterior instrumentation and fusion surgery with excellent clinical outcomes and a lower PJK occurrence.

Keywords: Adult degenerative scoliosis; Japanese Orthopaedic Association score; Low back pain; Lumbar Stiffness Disability Index; Lumbar lordosis; Oswestry Disability Index; Pelvic incidence; SRS-Schwab classification; Sagittal balance; Visual analog scale.