The severity of operative invasion to the posterior muscular-ligament complex influences cervical sagittal balance after open-door laminoplasty

The aim of this study was to investigate how the severity of operative invasion to the posterior muscular-ligament complex impacts postoperative cervical sagittal balance. Ninety cases of open-door expansive laminoplasty due to cervical spondylotic myelopathy were reviewed. Fifty-three patients underwent laminoplasty with unilateral preservation of the muscular-ligament complex (unilateral elevation group). Thirty-seven patients underwent traditional open-door laminoplasty (bilateral elevation group). Preoperative and postoperative cervical sagittal parameters, including C2-C7 sagittal vertical axis (SVA), C0-2 Cobb angle and T1 slope, were compared. The cervical curvature, range of motion (ROM) and JOA score were also compared. The average follow-up time was 16.7 months (range 3-40 months). C2-C7 SVA significantly increased in the bilateral elevation group (+4.9 mm, P = 0.005) but remained unchanged in the unilateral elevation group (-0.2 mm, P = 0.414). The C0-2 Cobb angle increased in both groups (+4.1A degrees, P < 0.001; +2.5A degrees, P = 0.002). The T1 slope also increased in both groups (+1.1A degrees, P = 0.015; +0.7A degrees, P = 0.042). The postoperative C3-C7 curvature significantly decreased in the bilateral elevation group (-4.1A degrees, P < 0.001). The C3-C7 ROM decreased in both groups (-17.9A degrees, P < 0.001; -15.1A degrees, P < 0.001). C2-C7 SVA was positively correlated with the T1 slope (Pearson = 0.468, P < 0.001) and negatively correlated with the C3-C7 curvature (Pearson = -0.322, P = 0.001). The C0-2 Cobb angle was positively correlated with C2-C7 SVA (Pearson = 0.303, P = 0.004) and negatively correlated with the C3-C7 curvature (Pearson = -0.362, P < 0.001). There was no significant between-group difference in the JOA improvement rate. Open-door laminoplasty significantly affected postoperative cervical sagittal balance, with the cervical vertebra appearing to tilt forward. As the severity of surgical invasion to the posterior muscular-ligament complex increased, the loss of cervical sagittal balance also increased.