Novel Biodegradable Composite of Calcium Phosphate Cement and the Collagen I Mimetic P-15 for Pedicle Screw Augmentation in Osteoporotic Bone

Abstract

Osteoporotic vertebral fractures often necessitate fusion surgery, with high rates of implant failure. We present a novel bioactive composite of calcium phosphate cement (CPC) and the collagen I mimetic P-15 for pedicle screw augmentation in osteoporotic bone. Methods involved expression analysis of osteogenesis-related genes during osteoblastic differentiation by RT-PCR and immunostaining of osteopontin and Ca²⁺ deposits. Untreated and decalcified sheep vertebrae were utilized for linear pullout testing of pedicle screws. Bone mineral density (BMD) was measured using dual-energy X-ray absorptiometry (DEXA). Expression of ALPI II (p < 0.0001), osteopontin (p < 0.0001), RUNX2 (p < 0.0001), and osteocalcin (p < 0.0001) was upregulated after co-culture of MSC with CPC-P-15. BMD was decreased by 28.75% ± 2.6%. Pullout loads in untreated vertebrae were 1405 ± 6 N (p < 0.001) without augmentation, 2010 ± 168 N (p < 0.0001) after augmentation with CPC-P-15, and 2112 ± 98 N (p < 0.0001) with PMMA. In decalcified vertebrae, pullout loads were 828 ± 66 N (p < 0.0001) without augmentation, 1324 ± 712 N (p = 0.04) with PMMA, and 1252 ± 131 N (p < 0.0078) with CPC-P-15. CPC-P-15 induces osteoblastic differentiation of human MES and improves pullout resistance of pedicle screws in osteoporotic and non-osteoporotic bone.

Keywords: calcium phosphate cement; collagen I mimetic P-15; osteoporosis; osteoporotic vertebral fractures; polymethylmethacrylate.

Figure 1

Osteodifferentiation of MESs in vitro. Using RT-PCR, mRNA expression of ALPI II (22.91 ± 0.011-fold, p < 0.0001), osteopontin (0.51 ± 0.1-fold, p < 0.0001), RUNX2 (0.65 ± 0.06-fold, p < 0.0001), osteonectin (2.92 ± 0.1-fold, p < 0.0001), and osteocalcin (8.64 ± 0.41-fold, p < 0.0001) were upregulated after treatment with CPC-P-15. * p < 0.05, ** p < 0.01, *** p < 0.005, **** p < 0.0005.

Figure 2

(A) Immunofluorescence staining of osteopontin and staining of Ca2+ deposits. (B) MESs cultured in a growth medium showed no osteopontin or Alizarin Red labeling When treated with CPC/P-15, osteopontin and Ca2+ deposits, colored red by the Alizarin Red staining, were detected after 10 days.

Figure 3

Axial pullout test and BMD in non-osteoporotic bone. (A) Pedicle screw placement in a skeletonized vertebra and set-up for pull-out testing. (B) F_max in untreated vertebrae was 1405 ± 56 N, in those with PMMA, 2112 ± 98 N (p < 0.0001), and 2010 ± 168 N (p < 0.0001) when augmented with CPC/P-15. There was no statistically significant difference between PMMA and CPC/P-15 treatments (p = 0.434). ** p < 0.01.

Figure 4

(A) Ovine osteoporosis model in vitro. (B) The BMD of the vertebrae of adolescent sheep was 0.72 ± 0.02 g/cm². (C,D) The BMD at the center of the mid-sagittal cross-section measured using CT was 511.8 ± 90.6 HU. BMD in the vertebrae of adolescent sheep treated with a decalcifying solution was 0.53 ± 0.04 g/cm². The BMD at the center of the mid-sagittal cross-section measured using CT was 101.3 ± 124.4 HU. The BMD was decreased by 28.75% ± 2.6%. **** p < 0.0005.

Figure 5

Axial pullout test and BMD in osteoporotic bone. In decalcified vertebrae, F_max was significantly lower (1405 ± 55.97 N) compared to not decalcified vertebrae (828 ± 66 N; p < 0.0001). F_max was significantly higher in those decalcified vertebrae augmented with CPC/P-15 (1252 ± 131 N; p < 0.0078) and those with PMMA (1308 ± 244 N; p = 0.04). There was no statistically significant difference between PMMA and CPC/P-15 (p = 0.94). ** p < 0.01, **** p < 0.0005.