Biomechanical effects of craniocervical instability on atlantoaxial lateral joint

Abstract

Object To analyze the effects of craniocervical junction instability caused by ligament resection on the neutral zones(NEs) and range of motions(ROMs) in C1-2 motion segment, and the maximum pressure of atlantoaxial lateral joint. Methods 6 cases of fresh cadaver specimens were used. By using the method of repeated measurements, NZs and ROMs in C1~2 motion segment were measured for normal control group and the craniocervical instability group under 2.0Nm and 1.0Nm pure moment loading of flexion extension, lateral bending and axial rotation, respectively. Results The NZs in C1~2 motion under the loadings of flexion and extension, lateral bending and axial rotation for craniocervical junction instability group were 26.67°±4.70°、9.13°±1.32°and 63.11°±5.87°, respectively. The NZs in C1~2 motion under the loadings of flexion and extension, lateral bending and axial rotation for craniocervical junction instability group were 14.12°±2.40°, 4.15°±0.75°and 50.75°±5.84°, respectively. The NZs in C1~2 motion segment for craniocervical instability group in the loadings of flexion and extension, lateral bending and axial rotation were significantly greater than those for intact group (P<0.05). The ROMs in C1~2 motion under the loadings of flexion and extension, lateral bending and axial rotation for craniocervical junction instability group were 42.37°±3.96°、13.67°±1.10°and 78.50°±4.00°, respectively. The ROMs in C1~2 motion under the loadings of flexion and extension, lateral bending and axial rotation for craniocervical junction instability group were 27.43°±2.41°、6.97°±0.59°and 65.26°±4.08°, respectively. The ROMs for craniocervical junction instability group in the loadings of flexion and extension, lateral bending and axial rotation significantly were higher than those for the intact group (P<0.05). For flexion, lateral bending and left axial rotation, the maximum stress of the atlantoaxial lateral joints for craniocervical instability group was less than that for the intact group. In the loadings of extension and right axial rotation, the maximum stress of the atlantoaxial right lateral joints for craniocervical instability group was less than that for the intact group, too.Howerer the atlantoaxial right lateral joint was unchanged under the extension laoding , and the left joint is a litte higher than that of the intact group under right axial loading. Conclusion Simple ligament resection in craniocervical junction could cause atlantoaxial instability. The range of motion for the loadings of flexion and extension, lateral bending and axial rotation is higher than that of the intact group. Atlantoaxial instability might lead to loss of load-bearing function of atlantoaxial lateral joint, and ultimately result in atlantoaxial dislocation. Key words: Craniocervical junction; Atlantoaxial lateral joint; Atlantoaxial dislocation; Stress; Range of motion