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.
Biopsy ; Needles ; Polymethyl Methacrylate ; Spine ; Vertebroplasty*