• Chris Yin Wei Chan, Chee Kidd Chiu, Yun Hui Ng, Saw Huan Goh, Xin Yi Ler, Sherwin Johan Ng, Xue Han Chian, Pheng Hian Tan, and Mun Keong Kwan.
• J Neurosurg Spine. 2020 Aug 28; 34 (1): 37-44.

ObjectiveThe incidence of postoperative shoulder imbalance following posterior spinal fusion (PSF) is still high in Lenke 1 curves despite following current treatment recommendations for upper instrumented vertebra (UIV) selection. The objective of this retrospective study was to identify differences in preoperative shoulder balance and to report the surgical outcome of two subtypes of Lenke 1 curves (flexible vs stiff) in patients with adolescent idiopathic scoliosis (AIS).MethodsThe authors grouped patients' curves as Lenke 1-ve (flexible) when their preoperative proximal thoracic side bending (PTSB) Cobb angle was < 15° and as Lenke 1+ve (stiff) when the PTSB Cobb angle was 15°-24.9°. The authors hypothesized that these two subtypes had distinct preoperative and postoperative shoulder and neck balance following PSF using pedicle screw constructs.ResultsFifty patients had Lenke 1 (flexible) curves and 61 had Lenke 1 (stiff) curves. The mean preoperative T1 tilt for patients with Lenke 1 (flexible) was -4.9° ± 5.3°, and for those with Lenke 1 (stiff) curves it was -1.0° ± 5.3° (p < 0.001). Mean cervical axis (CA) was -0.1° ± 3.2° for Lenke 1 (flexible) curves and 2.3° ± 3.5° for Lenke 1 (stiff) curves (p < 0.001). Preoperative radiographic shoulder height (RSH) and clavicle angle (Cla-A) were similar between the two curve subtypes. Following surgery, there were significant differences between the subtypes in terms of T1 tilt (p < 0.001), RSH (p = 0.014), and Cla-A (p = 0.031). Interestingly, 41.0% of patients with a Lenke 1 (stiff) curve had +ve T1 tilt compared to 2.0% in Lenke 1 (flexible) group. Moreover, 26.2% of patients with the Lenke 1 (stiff) curve had +ve RSH compared to 12.0% of those with Lenke 1 (flexible) curves. And, 24.6% of patients with Lenke 1 (stiff) had +ve Cla-A compared to 10.0% of those with Lenke 1 (flexible) curves.ConclusionsLenke 1 (flexible) and Lenke 1 (stiff) curves had distinct preoperative T1 tilt and CA measurements. Following PSF, the authors noted +ve T1 tilt in 41% of patients with Lenke 1 (stiff) curves versus 2.0% in those with Lenke 1 (flexible) curves. The authors also noted a significant difference in postoperative RSH and Cla-A measurements.

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