Optimizing surgical strategy in Lenke 5 C AIS patients with poor thoracic compensatory ability: is there a role of coronal imbalance?

PURPOSE: To investigate the effect of preoperative coronal balance patterns on the clinical outcome of Lenke 5 C patients with poor thoracic curve compensation ability following different fusion strategies. METHODS: Poor thoracic compensatory ability was defined as a thoracic cobb angle between 15° and 25° on supine bending films. Coronal balance patterns were classified as Type A (coronal balance distance (CBD)<20 mm), Type B (CBD > 20 mm and C7 plumbline (C7PL) shifted to concave side of main curve), and Type C (CBD > 20 mm and C7PL shifted to convex side of main curve), based on CBD and position of C7PL relative to main curve. Patients with preoperative Type C were classified into the Group Type C1(underwent selective fusion) and the Group Type C2(underwent non-selective fusion), and patients with preoperative Type A all underwent selective fusion surgery. Quality of life in preoperative Type C patients following different fusion strategies was assessed using the SRS-22 scale. RESULTS: Patients with preoperative Type C coronal pattern and poor thoracic compensatory ability showed a higher likelihood of thoracic curve progression after selective fusion surgery compared to Type A patients (48.7% vs. 20.9%, P = 0.007). In the Type A group, only 4.65% experienced thoracic curve progression exceeding 10°, while in the Type C1 group, this percentage was 21.95%. Additionally, at the last follow-up, 93.1% of Type A patients maintained good coronal balance, whereas 17.1% of Type C1 patients still had coronal imbalance. Type C2 patients who underwent non-selective fusion showed improved thoracic curvature from 34.86 ± 4.64° to 11.14 ± 4.30°, which was well maintained during follow-up. At the last follow-up, only 1 of 35 (2.8%) patients retained the Type C coronal pattern. The SRS-22 questionnaire showed that in Lenke 5 C AIS patients with preoperative Type C, the Type C2 group had significantly higher pain (4.33±0.51 vs. 3.87±0.55, P = 0.003) and self-image scores (4.88±0.10 vs. 4.55±0.50, P = 0.020) compared to the Type C1 group. CONCLUSION: For Lenke 5 C AIS patients exhibiting poor thoracic compensatory ability and preoperative Type C coronal imbalance, selective fusion demonstrated higher risks of proximal thoracic curve progression compared and inferior coronal balance restoration during follow-up. These findings suggest cautious consideration for preoperative coronal pattern and poor thoracic compensatory ability in Lenke 5 C AIS patients when planning surgery strategies.