Three-segment hybrid surgery for the treatment of noncontiguous cervical spondylosis:a finite element analysis

SUN Xiang-yao; HUANG Jiang; CAO Li; WANG Ju-yong; WANG Wei-liang; GAN Li-meng; LIU Yu-qi; ZHANG Qing-ming; LU Shi-bao

doi:10.3969/j.issn.2095-252X.2025.06.008

Abstract：Objective To simulate various forms of three-segment hybrid surgery for biomechanical analysis,providing references for the diagnosis and treatment strategies of multilevel noncontiguous cervical degenerative disease(CDD).Methods This study utilized CT data from 21 patients with CDD(10 males,11 females)to construct finite element models(FEMs).The focus was on surgical interventions at the C3/4,C5/6,and C6/7 segments.Two main hybrid surgical approaches were studied:Type Ⅰ FEM involved CDA at C3/4,ACDF at C5/6,and ACDF at C6/7;TypeⅡ FEM involved CDA at C3/4,CDA at C5/6,and ACDF at C6/7.The implanted structures used were AVS® Anchor-C and Synthes® Prodisc-C.In the FEM,an initial axial load of 73.6 N was applied using follower load technique at the motion center,and a torque of 1.0 Nm was applied at the center of C2 vertebra to simulate the movement of C2-7 FEM in all directions.Range of motion(ROM),average disc pressure,and facet joint contact stress at each segment were collected under various loading conditions.The t-test was used to compare differences between normally distributed continuous variables,while the Mann-Whitney U test was applied for comparing non-normally distributed or small sample variables.A significance level of P<0.05 was considered statistically significant.Results C4/5 segment forward flexion[(8.01±0.88)° vs.(7.20±1.18)°],dorsal extension[(6.92±1.42)° vs.(6.02±0.41)°]and axial rotation[(5.74±1.23)° vs.(4.75±0.47)°]ROM of Ⅰd type were higher than that of Ⅱd type,the differences were statistically significant(P<0.05).For the C3/4 segment,Ⅰd type dorsal extension[(6.58±0.60)° vs.(5.73±0.55)°],lateral bending[(7.25±0.58)° vs.(4.71±0.61)°],and axial rotation[(4.34±0.83)° vs.(3.84±0.54)°]ROM were significantly higher than Ⅱd type,and the differences were statistically significant(P<0.05).The ROM of the Ⅰd type at the C6/7 segment was higher than that of the Ⅱd type,while at the C5/6 segment,it was significantly lower than that of the Ⅱd type,and the differences were statistically significant(P<0.05).The Ⅰd and Ⅱd types showed similar flexion stability at the C2/3 and C3/4 segments,and the difference was not statistically significant(P>0.05).The average stress of C2/3 segment extension[(0.25±0.02)MPa vs.(0.25±0.03)MPa]and lateral bending[(0.35±0.02)MPa vs.(0.40±0.02)MPa]in Ⅰd type was significantly lower than that in Ⅱd type.The average stress of C4/5 segment extension[(0.28±0.04)MPa vs.(0.31±0.02)MPa]and lateral bending[(0.42±0.04)MPa vs.(0.47±0.03)MPa]in Ⅰd type was significantly lower than that in Ⅱd type,and the differences were statistically significant(P<0.05).However,the average pressure of C2/3 intervertebral discs of Ⅰd type was significantly higher than that of Ⅱd type[(0.40±0.03)MPa vs.(0.33±0.03)MPa],while the average pressure of C4/5 intervertebral discs of Ⅰd type was significantly lower than that of Ⅱd type[(0.44±0.03)MPa vs.(0.52±0.04)MPa],and the differences were statistically significant(P<0.05).There was no significant difference in facet joint contact stress between the Ⅰd and Ⅱd types at the C2/3 segment(P=0.088),while at the C4/5 segment,it was significantly reduced in the Ⅱd type[(84.58±8.65)N vs.(61.85±6.42)N],and the difference was statistically significant(P<0.05).Conclusions The three-segment Hybrid surgery will increase the overall ROM of non-fused segments.The Ⅰd type provides better protection against adjacent segment degeneration.The facet joint contact stress of non-fused segments in the Ⅱd type is significantly lower than that in the Ⅰd type.