Incorporating strategy in hybrid surgery for continuous two-level cervical spondylosis from a biomechanical perspective

Abstract

Background and objectiveHybrid surgery, incorporating cervical disc replacement and anterior cervical discectomy and fusion, has shown good clinical results in the treatment of multilevel cervical spondylosis according to early follow-ups. This study investigated the surgical strategy of hybrid surgery for two-level cervical spondylosis by distinguishing the biomechanical characteristics with different incorporating modes. MethodA finite element model of a healthy cervical spine including C2-T1 was developed, and hybrid surgery was simulated by replacing at one level with Prestige-LP and fusion at another level with the anterior plate in C3–C5 (Hybrid-S1: replaced at C3–C4, Hybrid-S2: replaced at C4–C5), and in C4–C6 (Hybrid-M1: replaced at C4–C5, Hybrid-M2: replaced at C5–C6) and in C5–C7 (Hybrid-U1: replaced at C5–C6, Hybrid-U2: replaced at C6–C7). The motion of C2 vertebrae in flexion, extension, axial rotation, and lateral bending was imposed on all hybrid models following the displacement control testing protocol. ResultsThe largest range of motion (ROM) in a healthy spine was observed at C5-C6, followed by C3-C4, C4-C5 and C6-C7. On average, the ROM at the replaced segment increased by 175.7%, 202.7%, 176.3%, 117.1%, 139.4%, and 236.0% in Hybrid-S1, Hybrid-S2, Hybrid-M1, Hybrid-M2, Hybrid-U1, and Hybrid-U2, respectively. The facet joint stress at the replaced segment increased by 186.9%, 124.4%, 111.1%, 60.3%, 62.7%, and 144.7%, and the adjacent intradiscal pressure (IDP) increased by 45.2%, 38.7%, 2.7%, 2.1%, 13.9%, and 20.1%. ConclusionsIncorporating mode in hybrid surgery affects cervical biomechanics. Hybrid surgery with replacement at a segment with a greater ROM and fusion at a segment with a lower ROM can results in fewer changes in terms of overall cervical stiffness, ROM at the operative level, facet joint stress, and adjacent IDP. In hybrid surgery, it is better to implement disc replacement at a level with a greater ROM and fusion of another segment.