Calcium Triglyceride Versus Polymethylmethacrylate Augmentation: A Biomechanical Analysis of Pullout Strength

Abstract

Study design: Biomechanical pullout study using calcium triglyceride (CTG) and polymethylmethacrylate (PMMA) for screw augmentation.

Objective: Compare the biomechanical performance of CTG augmentation versus the gold standard, PMMA, in primary and revision models, using a pedicle screw pullout model.

Background summary: CTG is a novel form of bone augmentation with several reported biocompatible properties compared with PMMA. PMMA is the standard of care for pedicle screw augmentation in osteoporotic spine.

Methods: Blocks of closed-cell rigid polyurethane foam of uniform density, representing subcortical layer in osteoporotic pedicle, were prepared according to ASTM standards. After the components of PMMA (n = 11) and CTG (n = 11) were individually mixed in a standardized fashion, 0.2 ml was injected from deep to superficial along a predrilled pilot hole followed by immediate insertion of the pedicle screw. An unaugmented group (n = 10) was also prepared. Blocks cured for 24 hrs, and screws were pulled out at a rate of 5 mm/min on materials testing equipment. For the revision model, the unaugmented group, after screw pullout, was augmented with 0.8 ml of PMMA (n = 5) or CTG (n = 5) as detailed above and screw pullout performed similarly.

Results: The mean pullout strengths (SD) for the intact models were as follows: unaugmented, 976.6 N (94.2 N); PMMA, 1,218.1 N (66.8 N); and CTG, 1,841.6 N (57.4 N). A one-way analysis of variance indicated a significant difference among the primary models (p < .0001). For the revision models, the pullout strength for PMMA was 1,939.2 N (108.9 N) and for CTG, 2,513.0 N (149.1 N), which were statistically different from each other (p < .0003). Stiffness of the constructs was increased with both PMMA and CTG augmentation over no augmentation (p < .0001) although no significant difference in stiffness was detected between the 2 forms of augmentation.

Conclusion: We conclude that CTG augmentation of pedicle screws resulted in significantly higher axial pullout strength in primary (p < .0001) and revision (p < .0003) models compared with PMMA.

Keywords: Augmentation; Calcium triglyceride; Pedicle screw; Pullout.