J Korean Soc Spine Surg.  2002 Jun;9(2):59-69.

Circumferential Bending Test of Lumbar 4-5 Segment and Biomechanical Investigation of Stability for Anterior Lumbar Interbody Cages and Supplemental Posterior Instrumentation

• An KC
• Choi JS
• Kim YC
• Shin DR
• Shin JW
• Kim JD
• Puno RM

Abstract

STUDY DESIGN: Compare the effectiveness of three types of cages used in each case separately with that of cages supplemented by posterior fixation such as transfacet screws and transpedicular screws.
OBJECTIVES
To determine whether any important information could be obtained when anterolateral and/or posterolateral bending is imposed. SUMMARY OF LITERATURE REVIEW: Most lumbar spine biomechanical bending tests have been performed on flexion-extension and lateral bending only.
MATERIALS AND METHODS
Flexibility was tested through the unconstrained eccentric compression-bending of isolated L4-L5 motion segments. A total of sixteen fresh frozen human cadaveric lumbosacral spine specimens(range of ages : 42+/-13 years 12 males and 4 females) were tested in this investigation. In each case bending load was applied in flexion(0 degree direction), then in 30 degree increments around the transverse plane until flexion was repeated at the 360 degree loading direction. Specimens underwent anterior interbody instrumentation with three different types of cage at L4-5 in three groups, respectively. After testing the interbody fusion constructs, the L4-L5 segments were first stabilized posteriorly using transfacet screws and then retested using transpedicular screw instrumentation.
RESULTS
In the intact model, the increase in deflection angle was twice compared with that of the previous point starting from 120 degree up to 150 degree. The pure extensional motion showed the largest deflection angles which are 3.5 times higher than those in pure flexion in average. All three types of cages showed the similar results that were obtained from the intact model.

MeSH Terms

Cadaver
Humans
Male
Pliability
Spine

Figure

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  Fig. 1. Specimen mounting (A. specimen with bending moment, B. specimen with the cage, C. specimen with anterior interbody cage and transfacet screws, D. specimen with anterior interbody cage and transpedicular screw with rods).

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  Fig. 2. Three kinds of cages used in this study (A. type A, B. type B, C. type C).

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  Fig. 3. Deflection angles measured at various points under bending moments.

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  Fig. 4. Comparison of deflection angles among the cages.

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  Fig. 5. Comparison of deflection angles among the surgical techniques at the same measuring point.

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  Fig. 6. The changes in deflection angles among the bending moment along the measuring point.

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