Stress distribution in zygapophyseal joint following two level artificial disc replacement under axial loading

Lei CHEN; Yizhao LI; Xiuwen ZHAO; Kanghua LI

ABSTRACT

BACKGROUND:

There is no study about adjacent zygapophyseal joint stress distribution following two level artificial disc replacement (ADR) in China.

OBJECTIVE:

To explore cervical adjacent zygapophyseal joint stress distribution following two level ADR and anterior cervical discectomy and fusion (ACDF),so as to provide biomechanical reference for clinical application of two level ADR.DESIGN,TIME AND

SETTING:

In vitro contrast observation and biomechanical detection were performed at the National Key Laboratory of College of Material Science and Engineering,Central South University from January to February 2006.MATERIALSA total of 11 fresh adult corpse cervical samples with intact cervical disc and ligament and the facet joint capsule ranged from C_3 to T_1 segment.

METHODS:

A total of 11 intact adult fresh-frozen multi-segmental cervical spine segments were utilized and biomechanically evaluated under the following C_(4～5),C_(5～6) cervical disc conditionsintact spine (intact group),Bryan disc prosthesis implantation (ACDR group) and intervertebral fusion (ACDF group).The testing was performed under axial load (25 N-150 N) on each group.The stress changes of the caudad (C_(5～6),C_(6～7)) zygapophyseal joint was tested.MAIN OUTCOME

MEASURES:

The pressure of the caudad (C_(5～6),C_(6～7)) zygapophyseal joint.

RESULTS:

Under axial loading,stress of the caudad (C_(5～6),C_(6～7)) zygapophyseal joint increased with the load and showed no difference between the intact group and ACDR group (P>0.05).Under axial loading,the ACDF group resulted in significant increase of the stress of the caudad (C_(5～6),C_(6～7)) zygapophyseal joint compared with intact group and ACDR group (P<0.05).

CONCLUSION:

Two level artificial cervical disc replacement can maintain stress in the caudad (C_(5～6),C_(6～7)) zygapophyseal joint,thus reconstruct biomechanical property of cervical spine.Two level cervical discectomy and fusion can increase stress in the caudad (C_(5～6),C_(6～7)) zygapophyseal joint,which may be one of the causes for adjacent cervical spondyiosis postoperatively.