RESUMO
Objective The finite element method was used to analyze the effect of height of bone graft on adjacent segment stress after anterior cervical decompression and fusion.Methods One healthy adult male was included in this study.A detailed,geometrically accurate three-dimensional cervical spine model had been successfully developed from computed tomography (CT) scanning of a healthy adult male.A pure moment of 1.0 N· m was applied in different directions on the upper endplate of C3 to simulate flexion,extension,left-right lateral bending,and left-right axial rotation.We did biomechanical experiment with goat cervical specimens in terms of the moment-rotation responses.The finite element (FE) model was compared and validated with the experimental data.The relevant data in the literature was also applied for comparison and validation.To construct the post-surgery model,we turned the property of disk annulus and disk nucleus into that of the cancellous bone at C4-5.The internal fixation systems were also implanted.We changed the height of bone graft in C4-5 to be 90％,150％,175％ and 200％ of the height between C4-5 pre-surgery.The finite element models were built to simulate the post-surgery scenarios with different bone graft height,respectively.A stress analysis was conducted on the bone graft and adjacent disks.Results Under different height of bone graft,the maximum yon Mises stress on C3-4 showed when the height of bone graft was 200％.The values were 0.99 MPa,0.85 MPa,0.91 MPa and 0.89 MPa in different loading condition.The values at 150％ of the height between C4-5 pre-surgery were only 81％,73％,80％ and 87％ of the values at 200％.For C5-6,the maximum yon Mises stress were 0.77 MPa,0.83 MPa,0.91 MPa and 0.81 MPa,observed at the height of bone graft was 175％ except extension.The values at 150％ of the height between C4-5 pre-surgery were only 76％,93％,86％ and 78％ of the biggest values.With regard to C4-5,the biggest yon Mises stress was 1.25 MPa,1.77 MPa,1.75 MPa and 1.81 MPa.It was observed when the height of bone graft was 200％ of the height between C4-5 pre-surgery.The values were smallest under height of 150％ of the height between C4-5 pre-surgery.The smallest values were 63％,63％,75％ and 52％ of the biggest values.The higher the bone graft was,the bigger the maximum von Mises stress on bone graft.In a word,it seems that the smallest stress was observed when the bone graft height was 150％.Concltusion The height of bone graft makes an important difference on the stress of adjacent segment after anterior cervical decompression and fusion.150％ of the height between C4-5 presurgery was proper bone graft height.In this case,the stress on the adjacent segments intervertebral disc is smaller.The probability of adjacent segments degeneration is smaller.
