Article
Adjustment of axial load characteristics of polyurethane foam in a porcine spine model for spondyloplasty
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Authors
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Witold Polanski
- Universitätsklinik Dresden, Carl-Gustav-Carus Universitätsklinikum an der Technischen Universität Dresden, Dresden, Deutschland
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Hongzhen Jiang
- Dresden, Deutschland
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Marek Molcanyi
- Köln, Deutschland
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Jozef Zivcak
- Kosice, Slovakia
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Daniel Ruess
- Köln, Deutschland
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Clemens Reinshagen
- Boston, United States
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Gabriele Schackert
- Klinikum Carl Gustav Carus, Klinik und Poliklinik für Neurochirurgie, Carl-Gustav-Carus Universitätsklinikum an der Technischen Universität Dresden, Dresden, Deutschland
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Bernhard Rieger
- Universitätsklinikum Carl Gustav Carus der TU Dresden, Klinik und Poliklinik für Neurochirurgie, Dresden, Deutschland
| Published: | June 9, 2017 |
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Outline
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Objective: Polymethylmetacrylate (PMMA) bone cement is widely used in the vertebral body. PMMA has about seven to ten times higher elastic modulus than normal cancellous bone what increases stiffness of PMMA augmented vertebral body by 174%. While augmentation with PMMA is highly successful in stiffer bony conditions, a significantly increased risk of adjacent fractures was found in osteoporosis. New osteoporotic fractures occurred at the adjacent levels after vertebroplasty with PMMA in 82%. Therefore, biomechanical axial load characteristics of adjustable polyurethane foam (PU foam) were analyzed in a porcine model for its alternative use as cancellous bone filler in osteoporosis or as a replacement of a vertebral body together with a new expandable device, made of titanium. In preparation of an intervertebral fusion concept in osteoporosis without using any pedicle screws adjustable PU foam as filler of vertebral cancellous bone was targeted. For the treatment of fractures or vertebral body replacement biocompatible and to lysine degradable foam was generated. For its use in osteoporosis, also non-biodegradable foam is available.
Methods: The adaptability of PU foam referring to compressive strength and stiffness was tested in a porcine model by comparing biomechanical behavior of vertebrae filled with PU foam with normal and hollowed vertebrae. Porcine lumbar vertebrae of pigs slaughtered at the age of 14 months were randomly split into four groups: A, B, C, D. Group A was normal vertebral body. Group B, C and D were defined hollowed with a specially designed router: through 8mm borehole ventral to the transverse process nearly complete cancellous bone was removed. This position of the borehole was chosen because the dorsolateral approach for implantation of a two-dimension expandable container was effective. Vertebrae of group C and D were filled with adjustable PU foams of different ratios. The compressive strength and stiffness of vertebral bodies in all four groups were recorded and analyzed.
Results: The strength and stiffness in all of the hollowed groups were lower than group A. However, the difference was not statistically significant between group A and group C (p>0.05), and were obviously different between group A and group B or group D (p<0.01 and <0.05). Moreover, the strength and stiffness after filling foams in group C or group D were significantly greater than in group B (p<0.01 and <0.05).
Conclusion: In developing a spinal fusion system for patients suffering from osteoporosis without the use of any pedicle screws there was a demand of an augmentation material of adjustable stiffness to avoid adjacent fractures in osteoporosis. This study compared the compressive strength and stiffness between vertebrae filled with new adjustable biocompatible PU foams and normal vertebrae in a porcine model to demonstrate its adaptability in stiffness according surgical requirements.
