title: Direct subcutaneous injection of polyethylene particles over the murine calvaria results in dramatic osteolysis.
abstract: OBJECTIVE
  The murine calvarial model has been widely employed for the in vivo study of particle-induced osteolysis, the most frequent cause of aseptic loosening of total joint replacements. Classically, this model uses an open surgical technique in which polyethylene (PE) particles are directly spread over the calvarium for the induction of osteolysis. We evaluated a minimally invasive modification of the calvarial model by using a direct subcutaneous injection of PE particles.
  
  
  METHODS
  Polyethylene (PE) particles were injected subcutaneously over the calvaria of C57BL6J ten-week-old mice ("injection" group) or were implanted after surgical exposure of the calvaria ("open" group) (n = 5/group). For each group, five additional mice received no particles and served as controls. Particle-induced osteolysis was evaluated two weeks after the procedure using high-definition microCT imaging.
  
  
  RESULTS
  Polyethylene particle injection over the calvaria resulted in a 40% ± 1.8% decrease in the bone volume fraction (BVF), compared to controls. Using the "open surgical technique", the BVF decreased by 16% ± 3.8% as compared to controls (p < 0.0001).
  
  
  CONCLUSIONS
  Direct subcutaneous injection of PE particles over the murine calvaria produced more profound resorption of bone. Polyethylene particle implantation by injection is less invasive and reliably induces osteolysis to a greater degree than the open technique. This subcutaneous injection method will prove useful for repetitive injections of particles, and the assessment of potential local or systemic therapies.
authors.affiliation: Department of Orthopaedic Surgery, Orthopaedic Research Laboratories, Stanford University School of Medicine, Stanford, CA, USA.
authors.forename: Allison J
authors.initials: AJ
authors.lastname: Rao
authors.forename: Stefan
authors.initials: S
authors.lastname: Zwingenberger
authors.forename: Roberto
authors.initials: R
authors.lastname: Valladares
authors.forename: Chenguang
authors.initials: C
authors.lastname: Li
authors.forename: Robert
authors.initials: R
authors.lastname: Lane Smith
authors.forename: Stuart B
authors.initials: SB
authors.lastname: Goodman
authors.forename: Christophe
authors.initials: C
authors.lastname: Nich
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D007279:Injections, Subcutaneous; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008863:Microspheres; D010014:Osteolysis / Q000139:chemically induced* / Q000473:pathology; D020959:Polyethylene / Q000008:administration & dosage* / Q000009:adverse effects* / Q000494:pharmacology; D012886:Skull / Q000000981:diagnostic imaging / Q000187:drug effects* / Q000473:pathology; D055114:X-Ray Microtomography
chemical_list: D020959:Polyethylene