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

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Abstract
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 (+4.1°, P < 0.001; +2.5°, P = 0.002). The T1 slope also increased in both groups (+1.1°, P = 0.015; +0.7°, P = 0.042). The postoperative C3–C7 curvature significantly decreased in the bilateral elevation group (−4.1°, P < 0.001). The C3–C7 ROM decreased in both groups (−17.9°, P < 0.001; −15.1°, 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.

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