J Korean Soc Spine Surg.  2006 Mar;13(1):16-22. 10.4184/jkss.2006.13.1.16.

Augmentation of Anterior Vertebral Screws Using Direct Anterior Vertebroplasty in the Porcine Model

• Lee DH
• Yoon KS
• Lee JH
• Kang SB
• Jo H
• Chang BS
• Lee CK
• Yeom JS

• KMID: 2040776
• DOI: http://doi.org/10.4184/jkss.2006.13.1.16

Abstract

STUDY DESIGN: A biomechanical study using the porcine spine.
OBJECTIVES
To investigate the efficacy of direct anterior vertebroplasty [Polymethylmetacrylic acid (PMMA) augmentation] with anterior vertebral screw fixation. SUMMARY AND LITERATURE REVIEW: We are not aware of any previous reports that described this technique.
MATERIALS AND METHODS
Thirty out of 35 fresh porcine lumbar vertebral bodies (L1-5) were instrumented with single anteriorvertebral screws using different augmentation methods. In group 1 (n=10), the non-augmented group, each vertebral body was pre-drilled and an anterior vertebral screw was inserted unicortically at 90 degrees laterally. In groups 2 (n=10) and 3 (n=10), after the unicortical pre-drilling, 2 ml of PMMA were injected through an 11-gauge bone biopsy needle. The screw was inserted immediately after the cement injection in group 2, and after complete consolidation of the cement in group 3. Axial pullout loads to loosen the screws were measured. Conventional vertebroplasties via bilateral pedicles were performed in the other 5 vertebral bodies, the cement distribution areas of which were compared with the 5 specimens of groups 2 and 3, respectively, using radiomorphometry. The data were analyzed using the Mann-Whitney test.
RESULTS
The mean pullout loads were 459+/-111N in group 1, 1510+/-165N in group 2, and 1241+/-189N in group 3. The PMMA augmented anterior vertebral screws (groups 2 and 3) provided more than 100% of an increase in pullout strength compared with non-augmented screws (group 1) (P < 0.001). Among the augmented screws, the screws that were inserted during the consolidation of PMMA (group 2) had a greater resistance against pullout loads than did those that were inserted after complete consolidation (group 3) (P < 0.01). The cement distribution areas after the direct anterior vertebroplasties (groups 2 and 3) was no different than that after conventional posterior vertebroplasties (P > 0.05)
CONCLUSIONS
Direct anterior vertebroplasty is another effective augmentation method for anterior vertebral screw fixation. With this technique, we avoided an unnecessary posterior procedure and achieved a more rigid fixation because we could insert the screws during the consolidation of PMMA.

Keyword

Anterior vertebral screw; Augmentation; Anterior vertebroplasty

MeSH Terms

Biopsy
Needles
Polymethyl Methacrylate
Spine
Vertebroplasty*
Polymethyl Methacrylate

Figure

• 

  Fig. 1. In group 1, a hole was created unicortically using 3.2-mm drill bit parallel to the coronal plane, toward the middle of the body, and midway between the endplates (A). A screw was inserted into the drilled hole (D). In group 2, after the unicortical drilling, 11-gauge bone biopsy needle was advanced and 2 ml of PMMA was injected manually (B). A screw was inserted just after the cement injection (during consolidation). In group 3, after the complete consolidation of injected cement, the hole was drilled again (C) and screw was inserted.

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  Fig. 2. In posterior vertebroplasty group, drill holes were made along bilateral pedicles. The bone biopsy needles were inserted into the drilled holes and 1ml of PMMA was injected on each side simultaneously.

• 

  Fig. 3. Tensile stress was loaded to failure in line with the long axis of screw at a displacement rate of 3.5 mm/min on an Instron electromechanical materials testing system (Instron 8500, Instron Corporation, USA). Pullout strength was defined as the load before a abrupt decrease in the load-deflection curve.

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  Fig. 4. Simple radiographs were made on both AP and axial planes to evaluate the distribution of injected PMMA. In PMMA augmented groups (group 2 and 3), the cement was evenly distributed into the vertebral body as seen in conventional posterior vertebroplasty.

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  Fig. 5. The measurement of cement distribution area on axial image using Image-ProⓇ Plus (Media Cybernetics, USA).

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  Fig. 6. The mean pullout strength. The PMMA augmented anterior vertebral screws (group 2 and 3) provided more than 100% of increase in pullout strength compared with non-augmented screws (group 1) (P<0.001). Among the augmented screws, the screws that were inserted during the consolidation of PMMA (group 2) had a greater resistance against pullout loads than did those that were inserted after complete consolidation (group 3) (P<0.01).

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  Fig. 7. The mean area of injected cement on AP and axial images. There was no significant difference between anterior (group 2 and 3) and posterior vertebroplasty groups.

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