Directionality of Lumbosacral Fractional Curve Relative to C7 Plumb Line, A Novel Index Associated with Postoperative Coronal Imbalance in Patients with Degenerative Lumbar Scoliosis

Study Design. Retrospective case-control radiographic study. Objective. The aim of this study was to explore whether directionality of lumbosacral fractional curve relative to C7 plumb line (PL) affected postoperative coronal imbalance in patients with degenerative lumbar scoliosis (DLS). Summary of Background Data. The spatial relationship between lumbar main curve and C7 PL was reported to have impact on postoperative coronal imbalance in DLS. Although fractional curve played more important role than lumbar main curve in DLS, the spatial relationship between fractional curve and C7 PL and their impact on the postoperative coronal balance are still unknown. Methods. One hundred one DLS patients treated with posterior instrumented fusion were reviewed. Coronal measurements included C7 migration, fractional curve, L4/L5 coronal tilt, major Cobb angle. Based on directionality of fractional curve (orientation of L4 coronal tilt was used to represent it) relative to C7 PL preoperatively, coronal patterns was separated into: consistency pattern, L4 coronally tilts toward C7 PL; opposition pattern, L4 coronally tilts opposite C7 PL; the distributions of these two patterns and Type A, B,C were analyzed. According to postoperative C7 migration, patients were divided into imbalanced group and balanced group. Results. Compared to balanced group, the imbalanced group had higher percentage of preoperative consistency pattern (80.6% vs. 33.8%, P < 0.001) and Type C (36.1% vs. 7.7%, P < 0.001); larger fractional curve or L4 coronal tilt pre- and postoperatively, larger L5 coronal tilt postoperatively. Logistic regression analysis showed predictors for postoperative coronal imbalance were consistency pattern (odds ratio [OR] 5.103, 95% confidence interval [CI]: 1.660-15.687, P = 0.004) and type C (OR 4.061; 95% CI: 1.056-15.618; P = 0.041). Conclusion. Directionality of fractional curve relative to C7 PL was associated with postoperative coronal imbalance in DLS patients. In addition to type C, consistency pattern might be an independent risk factor for postoperative coronal imbalance.

Automated summary

The directionality of the lumbosacral fractional curve relative to the C7 plumb line was found to be associated with postoperative coronal imbalance in patients with degenerative lumbar scoliosis. The consistency pattern might be an independent risk factor for postoperative coronal imbalance.