In vitro biomechanical comparison of three anterior cervical fixation methods

English Keywords:Biomechanics  Cervical fusion  Goat cadaver specimen

English Abstract:

  【Abstract】 Objectives: To compare the immediate stabilities of Zero-profile inter-body fusion device(Zero-P) and polyetheretherketone(PEEK) assembled plate-cage fusion device(the Skate) with conventional titanium plate fixation in single-level anterior cervical discectomy and fusion(ACDF) through biomechanical test in fresh cadaver specimens. Methods: 24 fresh cervical vertebra specimens were collected from 24 male goats (C3-4), and X-ray and bone mineral density examinations were performed to exclude fracture, deformities and osteoporosis. Muscles were removed and main ligaments, joint capsule, and intervertebral discs were preserved. The vitro biomechanical tests of flexion-extension, lateral bending and torsion were performed on 24 goat cervical spine specimens(normal group) and the loading conditions were an axial load of 20N and a kinematic load of 2.5N·m. The range of motion(ROM) and neutral zone(NZ) were collected. And then, the specimens were randomly divided into 3 groups: Titanium plate group(n=8), C3/4 discectomy and intervertebral fusion and anterior fixation by conventional titanium plate; Zero-P group(n=8), C3/4 intervertebral fusion and fixation with Zero-P device; and Skate group(n=8), C3/4 intervertebral fusion and fixation with Skate. Motion simulations were performed in the three groups again under the same loading conditions as the normal group, and the ROMs and NZs were recorded. Results: Postoperative imaging showed that the positions of the prostheses were normal. The titanium group: the ROMs of before fixation in flexion, extension, lateral bending and torsion were 9.22°±1.12°, 6.34°±0.54°, 15.21°±1.28°, 1.55°±0.30°, the ROMs of after fixation were 1.30°±0.30°, 1.36°±0.40°, 1.39°±0.39°, 0.94°±0.18°, which were significantly reduced compared with before fixation(P<0.05). The Zero-P group: the ROMs of before fixation were 9.33°±1.29°, 6.60°±0.37°, 15.06°±1.42°, 1.64°±0.22°. The ROMs of after fixation were 1.50°±0.10°, 1.59°±0.51°, 1.75°±0.69°, 0.75°±0.25°, which were significantly reduced compared with before fixation(P<0.05), and were with no significant difference compared with after fixation of titanium group. The Skate group: the ROMs of before fixation were 9.43°±1.17°, 6.64°±0.43°, 15.15°±1.21°, 1.69°±0.17°, the ROMs of after fixation were 2.50°±0.20°, 6.42°±1.89°, 8.26°±1.00°, 0.87°±0.21°, which, comparing with before fixation, decreased significantly in flexion， lateral bending and torsion condition(P<0.05), but not significantly different in extension condition(P>0.05); and which increased significantly in flexion, extension and lateral bending(P<0.05) comparing with after fixation of titanium group, but not significantly different in torsion condition(P>0.05). The titanium group: the NZs of before fixation in flexion-extension, lateral bending and torsion were 8.38°±1.18°, 27.05°±2.96°, 0.77°±0.27°, NZs of after fixation were 1.12°±0.37°, 1.17°±0.54°, 0.47°±0.17°, which were significantly reduced compared with before fixation(P<0.05). The Zero-P group: the NZs of before fixation were 8.14°±0.95°, 27.67°±1.73°, 0.68°±0.28°, the NZs of after fixation were 1.41°±0.54°, 1.99°±0.71°, 0.34°±0.12°, which were significantly reduced compared with before fixation(P<0.05), and were with no significant difference compared with after fixation of titanium group(P>0.05). The Skate group: the NZs of before fixation were 8.06°±0.73°, 27.41°±2.53°, 0.64°±0.27°, NZs of after fixation were 5.13°±1.48°, 7.17°±1.74°, 0.47°±0.18°, which were significantly reduced compared with before fixation(P<0.05). Comparing with after fixation of titanium group, which increased significantly in flexion-extension and lateral bending(P<0.05), yet not significantly different in torsion condition(P>0.05). Conclusions: Zero-P has the similar mechanical properties as the traditional titanium plate, while Skate is weaker in mechanical properties than the traditional titanium plate.