Biomechanical evaluation for single-level rigid fixation combined with Coflex implantation

English Keywords:Rigid fixation  Interspinous divece  Biomechanical test

English Abstract:

  【Abstract】 Objectives: To evaluate the biomechanical effect of topping-off operation with Coflex interspinous dynamic device combined with adjacent monosegmental rigid fixation by pedical screw in lumbar spine. Methods: 6 fresh frozen human cadaveric lumbar spine specimens(6 males) were tested. Models of L4/5 rigid fixation by pedical screw(posterior lumbar interbody fusion, PLIF) and models of L4/5 rigid fixation by pedical screw combined with L3/4 Coflex were established. On each specimen, range of segmental motion(ROM) and intradiscal pressure(IDP) of L3/4 and L5/S1 were tested in the condition of intact(group A), rigid fixation(L4/5)(group B) and combined with Coflex(L3/4)(group C), respectively. Results: The L3/4 ROM of group B was higher than that of group A significantly(P<0.05). The L3/4 ROM of group B in flexion, extension, lateral bending and axial rotation increased by 0.54°, 0.34°, 0.30° and 0.19°, respectively. The L5/S1 ROM of group B increased with no statistical significance(P>0.05), compared with group A. The L3/4 ROM of group C was lower than that of group B(P<0.05) only in the extension, while the decreases were not significant in other directions. Compared with group A, the L3/4 ROM of group C did not increase significantly in the extension and axial rotation(P>0.05), while it increased significantly in flexion(0.38°) and lateral bending(0.28°), respectively. Compared with group B, the L5/S1 ROM of group C had a increasing trend in extension, lateral bending and axial rotation, but no statistical significance(P>0.05). Compared with group A, the L5/S1 ROM of group C had a increasing trend in all directions(P>0.05). The L3/4 IDP of group B was higher than that of group A(P<0.05). The L3/4 IDP of group B in flexion, extension, lateral bending and axial rotation increased by 1.82kPa, 1.88kPa, 1.84kPa and 1.45kPa, respectively. The L5/S1 IDP of group B in flexion, extension, lateral bending and axial rotation increased by 1.21kPa, 0.94kPa, 0.70kPa and 0.81kPa, respectively(P<0.05). The L3/4 IDP of group C was lower than that of group B only in the extension(P<0.05). Compared with group A, the L3/4 IDP of group C in flexion, lateral bending and axial rotation increased by 1.53kPa, 1.71kPa and 1.35kPa, respectively(P<0.05). Compared with group B, L5/S1 IDP of group C increased in lateral bending and axial rotation, but no statistical significance(P>0.05). Compared with group A, L5/S1 IDP of group C in flexion, extension, lateral bending and axial rotation increased by 0.82kPa, 0.84kPa, 0.85kPa and 0.99kPa, respectively(P<0.05). Conclusions: Biomechanical evidence supports the protective effect of interspinous device on upper adjacent segments after monosegmental rigid fixation. It may increase the stress of lower adjacent segment which may induce adverse effects in the long-term period.