The effect of intraosseous injection of simvastatin into the lumbar vertebrae on vertebral bone microstructure and stability of pedicle screw in osteoporotic miniature pigs

English Keywords:Simvastatin  Intraosseous injection  Osteoporosis  Pedicle screw  Stability  Miniature pigs

English Abstract:

  【Abstract】 Objectives: To study the effect of intraosseous injection of simvastatin/poloxamer 407 gel into the lumbar vertebrae on vertebral bone microstructure and stability of pedicle screw in osteoporotic miniature pigs. Methods: Nine female mature Guangxi BA-MA miniature pigs received bilateral ovariectomy(OVX) and feeded with the calcium-restricted diet in order to establish the model of osteoporosis. The bone mineral density(BMD) of pig lumbar was examined before the bilateral OVX and 18 months after the bilateral OVX, the BMD decreased by 25.23%, which could be used as the successful establishment of osteoporotic pig. Three lumbar vertebrae(L4-L6) in each miniature pig were divided into three groups randomly after the establishment of osteoporotic pig. Blank vector(0mg), 0.5mg, 1mg simvastatin was once injected into the left side of pilot hole on the lumbar vertebrae(L4-L6) of experimental pigs. After the injection, titanium alloy pedicle screw was inserted through the pilot hole bilaterally. All animals were sacrificed and lumbar vertebrae(L4-L6) were harvested at 3 months after the injection, respectively. All the lumbar vertebrae were disarticulated and dissected free of soft tissue to yield individual vertebra. The samples were collected for BMD, bone microstructure and biomechanical pull-out test analysis by using dual energy X-ray absorptiometry(DXA), micro-computed tomography(Micro-CT) and the Bionix Servohydraulic Test System. BMD, bone microstructural parameters and the maximum pull-out strength were recorded. Results: Compared with pre-treatment, BMD of SIM 0.5mg and 1.0mg increased by 32.12% and 28.16%, respectively, compared with SIM 0mg, BMD of SIM 0.5mg and 1.0mg increased by 31.25% and 31.09%(all P＜0.01), respectively. Compared with SIM 0mg, SIM 0.5mg and 1.0mg significantly increased BV/TV by 47.49% and 43.42%, Tb.N by 49.23% and 39.01%, Tb.Th by 66.09% and 54.28%, %OI by 46.54% and 42.63%, decreased Tb.Sp by 55.85% and 52.80%(all P＜0.01), respectively. Compared with SIM 0mg, the pull-out strength of SIM 0.5mg and SIM 1.0mg significantly increased by 45.75% and 51.53%(both P＜0.01). Histological test found large amount of peri-implant trabecular bone in the single, local simvastatin injection groups and screw-bone interfaces increased. Conclusions: Single intraosseous injection of simvastatin/poloxamer 407 gel into the lumbar vertebrae can stimulate bone formation, which can increase the BMD and also improve bone microstructure, finally enhances strength of pedicle screw in osteoporotic miniature pigs.