Study design:

Retrospective case-control radiographic study.

Objective:

To identify main effects of preoperative pattern and global coronal malalignment (GCM) on postoperative coronal imbalance in degenerative lumbar scoliosis (DLS) patients and evaluate the rationality of the classification of coronal deformity based on preoperative GCM. A classification of coronal deformity based on preoperative GCM (20 mm set as the threshold of coronal imbalance) has been proposed recently, but whether it is practical is unclear.

Methods:

One hundred twelve DLS patients treated with posterior instrumented fusion were reviewed. Coronal measurements included GCM and major Cobb angle. Based on relationship between C7 PL and major curve, preoperative patterns were classified into: Pattern 1(concave pattern), C7 PL shifted to the concave side of major curve; Pattern 2(convex pattern), C7 PL shifted to the convex side of major curve. Patients were separated into 4 groups (3 types): Type 0-1: GCM < 20 mm plus Pattern 1; Type 0-2: GCM < 20 mm plus Pattern 2; Type 1: GCM > 20 mm plus Pattern 1; Type 2: GCM > 20 mm plus Pattern 2. After comparison within patterns or among 4 groups, further factorial analysis was performed.

Results:

Significant differences regarding postoperative GCM or coronal imbalance/balance ratio existed among 4 groups (F = 6.219, p = 0.001; x² = 22.506, p < 0.001, respectively), despite no significant difference in intra-pattern 1(concave pattern) or intra-pattern 2(convex pattern) groups. Two-way analysis of variance showed preoperative pattern exhibited significant effect on postoperative GCM or imbalance/balance ratio (F_(1,108) = 14.286, p < 0.001; F_(1,108) = 30.514, p < 0.001, respectively) while neither preoperative GCM alone nor interaction of preoperative GCM with pattern did.

Conclusion:

In DLS patients, it’s the preoperative pattern other than GCM that had main effects on postoperative coronal imbalance. Classification of coronal deformity based on preoperative GCM is questionable.