Adjacent segment biomechanical changes after one- or two-level anterior cervical discectomy and fusion using either a zero-profile device or cage plus plate: A finite element analysis.

Anterior cervical discectomy and fusion (ACDF) is a well-established surgical treatment for patients with symptomatic cervical degenerative disc disease, while the biomechanical changes of adjacent segments after ACDF using either a zero-profile device or cage plus plate remain uncertain. The present study is to compare adjacent segment biomechanical changes after one- or two-level ACDF using either a zero-profile device or cage plus plate. A three-dimensional finite element (FE) intact cervical model (C2-C7) was constructed and validated. In the one-level surgery model, either a zero-profile device or cage plus plate was implanted at the C5-C6 segment of the model; while in the two-level surgery model, the prostheses were implanted at the C4-C5 and C5-C6 segments of the model. A pure moment of 1.0 Nm combined with a follower load of 73.6 N were imposed on C2 to determine the flexion-extension, lateral bending, and axial rotation of different segments. The segmental range of motion (ROM) and maximum value of the intradiscal pressure of the surgery models were determined and compared with those of the intact model. In both one- and two-level ACDF models, the ROM of the fused segments was sacrificed, while loss of ROM at the fused segments was greater in cage plus plate models than in zero-profile device models because of structural differences of the implanted devices. However, the ROM and intradiscal pressure were increased at the C4-C5 and C6-C7 segments in the one-level model of ACDF using either a zero-profile device or cage plus plate, the ROM and intradiscal pressure were also increased at the C3-C4 and C6-C7 segments in the two-level surgery models. In conclusion, decreased ROM was observed at the fused segments, while increased ROM and intradiscal pressure were observed at the adjacent segments of the fused segments in ACDF, regardless of whether zero-profile devices or cage plus plate was used. Moreover, loss of ROM at the fused segments was greater in cage plus plate models than in zero-profile device models.