Biomechanics of different fixed patterns of low lumbar spine

Abstract

Objective To observe the effects of different fixed patterns on low lumbar spine stability.Methods The spine specimens from 6 fresh adult cadavers were divided into five groups:group A (normal low lumbar vertebrae specimen) ; group B (unilateral translaminar facet screw fixation and interbody fusion) ; group C (unilateral pedicle screw and interbody fusion) ; group D (unilateral pedicle screw combined with contralateral translaminar facet screw fixation and interbody fusion) ; group E (bilateral pedicle screw and interbody fusion).A biomechanical test of compression in flexion,extension and lateral bending,as well as axial rotation,angular range of motion (Rom) and value of hardness was done.Results As compared with group A,ROM under every state of motion was decrease,and the stiffness was significantly increased in group B (P ＜ 0.05 ).There was no significant difference in ROM and stiffness between groups B and C ( P ＞ 0.05 ).As compared with group C,ROM was reduced and stiffness increased in group D (P ＞ 0.05).There was no significant difference in ROM and stiffness between groups D and E (P ＜ 0.05 ).As compared with group E,ROM was increased,and stiffness decreased significantly in group C (P ＜ 0.05).Conclusion Unilateral laminar facet screw fixation with bone graft fusion cage method provides a certain stability,and unilateral pedicle screw combined with contralateral translaminar facet screw fixation and interbody fusion provides the same stability as bilateral pedicle screw fixation.The two fixed patterns can be applied on the specific situations of the cases,as for baric index,pathclogical features and the stability of segmengtal lesions. Key words: Low lumbar spine; Screw; Fixation; Interbody fusion; Stability