Biomechanical Effects of Fixation of Different Segments of Goat Lumbar Spine on Adjacent Segmental Motion and Intradiscal Pressure Change

Abstract

BACKGROUND The aim of this study was to investigate the biomechanical fixation effects of different segments of the goat spine on adjacent segmental motion and intradiscal pressure (IDP) change. MATERIAL AND METHODS Eighteen goat spine specimens were randomly divided into 3 groups: group A (single-segment fixation), group B (double-segment fixation), and group C (triple-segment fixation). The motion was tested on each specimen using a spinal motion simulation test system with rational pressure loading. The IDP was measured using a pinhole pressure sensor. RESULTS Range of motion (ROM) and IDP of adjacent segments increased with increased external load. In comparison of the 3 groups, significant differences in ROM were found when the external force was more than 100 N (P<0.05). The differences in IDP of the adjacent segment were statistically significant (P<0.05) when external pressure was greater than or equal to 60 N. However, in comparison of group A with group B, no significant differences in ROM and IDP of the adjacent segments were noted for the motions of anterior flexion, posterior extension, and lateral bending (P>0.05). Moreover, upper adjacent segments had greater ROM than the lower adjacent segments (P<0.05). We found significant differences between IDPs of the upper adjacent segments and lower adjacent segments (P<0.05). CONCLUSIONS As the number of fixated lumbar segments increases, ROM and IDP of the adjacent segments increase. Multisegment fixation is most likely the main factor contributing to the development of adjacent segmental lesions after lumbar fixation.

Figure 1

Experimental equipment.

Figure 2

Successful specimen model and its X-ray imaging.

Figure 3

Definition of direction of motion during the testing process.

Figure 4

Measurement results of transverse displacement, forward-backward displacement, and vertical displacement in different motion directions, TD – transverse displacement; FD – forward-backward displacement; VD – vertical displacement; A1, A2, A3 represent TD, FD, and VD at the upper adjacent segments, respectively; B1, B2, B3 represent TD, FD, and VD at the lower adjacent segments, respectively.

Figure 5

The adjacent segmental IDP. (A) IDP at the upper adjacent segments; (B) IDP at the lower adjacent segments.