An in vivo murine model of continuous intramedullary infusion of polyethylene particles

Abstract

Wear debris affects both initial osseointegration and subsequent bone remodeling of total joint replacements (TJRs). To study the complex cascade associated with the continuous generation of particles, a robust animal model is essential. To date, an animal model that incorporates continuously delivered particles to an intramedullary orthopaedic implant has not been available. In this study, we successfully infused clinically relevant ultra high molecular weight polyethylene particles, previously isolated from joint simulator tests, to the intramedullary space of the mouse femur for 4 weeks using a subcutaneous osmotic pump. Reduction of bone volume following the 4-week infusion of UHMWPE was detected by microCT. UHMWPE particles also changed the level of Alkaline Phosphatase expression in the infused femurs. Continuous infusion of particles to the murine bone-implant interface simulated the clinical scenario of local polymer wear particle generation and delivery in humans and can be used to further study the biological processes associated with wear debris particles.

Biological Response of Osteoblasts and Osteoprogenitors to Orthopaedic Wear Debris

“…A study has compared the two approaches in mice and shown successful delivery of 10 L volumes of 10% PMMA particles into the femoral canal, confirmed subsequently by micro-CT imaging (Zilber et al, 2008). The efficiency of this in vivo particle infusion system has been determined in a series of studies (Ortiz et al, 2008a(Ortiz et al, , 2008bMa et al, 2008Ma et al, , 2009a. In this series, the Alzet miniosmotic pump delivered UHMWPE and polystyrene particles (0.5 ± 0.015 m) over 4 weeks into an ex vivo collection tube.…”

Continuous Infusion of UHMWPE Particles Induces Increased Bone Macrophages and Osteolysis

“…The murine macrophage cell line RAW264.7 was transfected with the lentiviral vector to express the bioluminescent optical reporter gene, firefly luciferase (fluc), and a fluorescence reporter gene, green fluorescent protein (gfp), as previously described [7]. Prior power analysis was based on published data using a similar experimental design [25]. To detect a difference of 1.5 standard deviations from the mean for BLI and bone mineral density (BMD) with a power of 80% (a = 0.05, b = 0.20), nine animals would be needed in each group.…”

“…We strictly followed Stanford University's guidelines for the care and use of laboratory animals. The murine continuous femoral intramedullary infusion model used in this study was modified from a previously described rat model [22] and validated by successfully pumping UHMWPE and blue polystyrene particles into murine femoral medullary canals [25,31,32].…”

“…Instead of pumping particles into the knee and inserting a solid wire into the femoral medullary canal, we modified the rat model of Kim et al [18,22] by implanting a hollow titanium rod in the distal part of the femur and pumping particles into the femoral bone marrow cavity directly. In this modified mouse model, polyethylene particles were infused continuously into the femur through an osmotic pump to simulate the clinical scenario more closely [25,26,31,32].…”

Exogenous MC3T3 Preosteoblasts Migrate Systemically and Mitigate the Adverse Effects of Wear Particles

“…The procedure was adapted from a previously described rat model 31 and has been validated. 32,33 The animals were anesthetized using 3%-5% isoflurane in 100% oxygen and kept on a warm, sterile small animal surgery station. A medial parapatellar incision was made and the medullary cavity was exposed via the intercondylar notch of the distal left femur.…”