Browsing by Author "Zhong, Z. C."

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Biomechanical Differences of Coflex-F and Pedicle Screw Fixation in Stabilization of TLIF or ALIF Condition - A Finite Element Study
(2010)
Lo, C. C.
;
Tsai, K. J.
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Zhong, Z. C.
;
Hung, C.
;
機械工程學系
Lumbar interbody fusion is a common procedure for treating lower back pain related to degenerative disc diseases. The Coflex-F is a recently developed interspinous spacer, the makers of which claim that it can provide stabilization similar to pedicle screw fixation. Therefore, this study compares the biomechanical behavior of the Coflex-F device and pedicle screw fixation with transforaminal lumbar interbody fusion (TLIF) or anterior lumbar interbody fusion (ALIF) surgeries. This study used a validated three-dimensional finite element model of the L1-L5 lumbar intact spine. To simulate TLIF surgery, left lateral total facetectomy and partial discectomy were performed at the L3/L4 segment of this intact model. An AVS-TL moon cage (Stryker Orthopaedics) was implanted in the L3/L4 segment and using a Coflex-F device or pedicle screw fixation. To simulate ALIF surgery, partial discectomy and total nuclectomy were performed at the L3/L4 segment of this intact model. A SynCage-Open cage (Synthes Spine, Inc.) was implanted into the L3/L4 segment and combined with a Coflex-F device or pedicle screw fixation. A 400 N follower load and a 10 Nm moment were applied to the intact model to mimic four physiological motions. All four implanted models were subjected to 400 N follower load and specific moments in accordance with the hybrid test method. The results show that the Coflex-F device combined with ALIF surgery can provide stability similar to that of pedicle screw fixation combined with TLIF or ALIF surgery. Also, both the posterior instrumentations (Coflex-F and pedicle screw fixation) combined with TLIF surgery had lower stability than combined with ALIF surgery.
Effect of the Cord Pretension of the Dynesys Dynamic Stabilization System on the Biomechanics of the Lumbar Spine: A Finite Element Analysis
(2010)
Zhong, Z. C.
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Liu, C. L.
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Hsu, H. W.
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Yang, B. S.
;
Chen, C. S.
The basic concept of the Dynesys dynamic stabilization system is to reduce the stiffness of the rigid fixation system to allow limited motion at the implanted level and to prevent stress concentrated at adjacent levels. However, the magnitude of cord pretension may change the stiffness of the Dynesys system and result in diverse clinical outcome, but the effects of Dynesys cord pretension remain unclear. Displacement-controlled finite element analysis was used to evaluate the biomechanical behavior of the lumbar spine after insertion of Dynesys with three different cord pretensions. For the implanted level, increasing the cord pretension from 100 to 300N resulted in an increase in stiffness in flexion from 19.0 to 64.5Nm/degree, and an increase in the high stress region of pedicle screw in flexion and lateral bending. For the adjacent levels, varying the cord pretension from 100 to 300N only has a minor influence on range of motion (ROM) of 6%. This study found that alteration of cord pretension affects the ROM within construct but not significantly to the adjacent segment. In addition, use of a 300N cord pretension causes a much higher stiffness at the implanted level when compared with the intact lumbar spine.