A Normal PI-LL Relationship is Associated With Pain Improvement Following Posterior Spinal Fusion for Scheuermann Kyphosis

Background: Pelvic incidence-lumbar lordosis (PI-LL) mismatch is a validated marker of sagittal balance that correlates with pain and HRQoL in adult spinal deformity. The purpose of this study was to investigate whether there is an association between a normal postoperative pelvic incidence-lumbar lordosis (PI-LL) relationship and pain improvement at 2 years following PSF for SK. Methods: SK patients who underwent PSF and reached 2 years postoperative were identified in a multicenter registry. Patients with anterior release, prior spine surgery, neuromuscular comorbidity, or posttraumatic/postlaminectomy kyphosis were excluded. A normal PI-LL relationship (<10° difference; either correction of mismatch OR maintenance of normal) was determined at 2 years. Improvement in pain was defined as a 2-year postoperative increase in SRS-22 pain score of more than or equal to the minimal clinically important difference. Results: Of the 91 patients who were eligible, 50 (16.2±1.6 y/o, 68% male) had radiographic and health-related quality of life (HRQoL) data available for analysis. Preoperative and 2-year postoperative major kyphosis were 74±11° and 48±9°, respectively. The average pain score was 3.9 [interquartile range (IQR): 3.4 to 4.4] at preoperative and 4.4 (IQR: 4.0 to 5.0) at 2-year postoperative ( P =0.002). Only 4 (8%) patients had normal PI-LL at preoperative, increasing to 19 (38%) patients at 2 years postoperative. In those with normal postoperative PI-LL, 68% (N=13) had improvement in pain, compared with 42% (N=13) in those with PI-LL mismatch ( P =0.069). Patients with normal postoperative PI-LL had an increased likelihood of pain improvement by 1.63 (95% CI=0.98, 2.73) times when compared with those with PI-LL mismatch ( P =0.062). Conclusion: Improvements are observed in both PI-LL measures and pain scores following PSF for SK at 2 years postoperatively. Patients with normal PI-LL postoperatively (corrected or maintained) had an increased likelihood of pain improvement. Level of Evidence: Level III—retrospective case–control study.