Biomechanical analysis of the patient-specific appropriate correction angle for cervical kyphosis in multilevel anterior cervical discectomy and fusion: a finite element analysis.

backgroundThe correction angle of cervical kyphosis affects both treatment outcomes and the risk of postoperative complications. Incorrect correction can increase pressure on nearby discs, causing segment degeneration, and may overload implants, leading to failure. No clear medical conclusions and applicable methods exist for determining the appropriate spinal correction angle to achieve lasting deformity correction. This paper aimed to prove the existence of a specific appropriate angle from a biomechanical perspective and provide a method for its accurate determination.

methodsThree patients A, B, and C, with severe cervical kyphosis, were selected for Computed Tomography imaging, and each one was used to reconstruct six C1-C7 finite element models with altering correction angles following multilevel anterior cervical discectomy and fusion. The biomechanical differences were compared under 73.6 N axial load with 1 Nm moments and uniaxial 73.6 N compressive loading. Following the simulation, a weighted evaluation scheme was proposed to determine an appropriate correction angle.

resultsAll patient-specific models displayed consistent biomechanical performance when correction angles varied. Adjacent C2-C3 segments exhibited greater flexion mobility under low correction angles and increased extension under high angles. The moderate correction models showed more uniform Von Mises stress. Quantitative analysis revealed a U-shaped trend in the maximum and average stress levels across intervertebral discs, facet joints, vertebrae, and implants for all three patients. For example, in Patient A, the Von Mises stress of the cage decreased from 5.06 MPa at 40° to 1.50 MPa at 20°, then increased to 7.51 MPa at - 10°. Based on the comprehensive scoring of correction models, the recommended appropriate correction angles for the three patients were as follows: A 10°, B 17°, and C 0°.

conclusionsThe results indicated that moderate correction angles could reduce mechanical stress and lower the risk of postoperative complications. The link between biomechanical data and complications after cervical kyphosis correction supported the existence of an appropriate correction range. It helped to guide the personalized surgical planning from implant selection to the specific intraoperative operations performed by the surgeon and implant design optimization.