A controlled experimental model of revision implants: Part I. Development.
We investigated the roles of particulate matter with unstable implant, in engendering the aggressive tissue response associated with implant loosening in humans. This study serves as a basis for establishing a controlled animal model to reproduce the conditions present after implant loosening. The model includes a 6 mm polymethylmethacrylate (PMMA) cylinder concentrically pistoning 500 microm under load in a 0.75-mm circumferential gap, inserted into canine medial femoral condyles for 8 weeks. We evaluated two size concentrations of polyethylene: type A particulate polyethylene (0.5-12 microm), and type B particulate polyethylene (0.5-50 microm; 85% < 12 microm). The following three treatment groups were investigated in 28 unstable implants in 14 dogs: (1) without polyethylene (control), (2) with type A polyethylene, and (3) with type B polyethylene. We found an aggressive periprosthetic membrane, similar to that seen at revision in humans, only in the unstable implant with polyethylene. The features of this membrane included macrophages with intracellular polyethylene, a dense fibrous membrane with a synovial-like lining layer, and a sclerotic neocortex. The size distribution of the polyethylene did not alter the tissue response. An unstable implant without polyethylene resulted in a benign, quiescent membrane with loose fibrous connective tissue. The model creates a revision cavity analogous to that seen in revision joint arthroplasty, and merits further studies of revision joint replacement.
Bechtold
J E
JE
The Orthopaedic Biomechanics Laboratory, Hennepin County Medical Center/Midwest Orthopaedic Research Foundation, Minneapolis, MN 55404, USA. jbechtold@morfn.org
Kubic
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D000818:Animals; D001672:Biocompatible Materials; D004285:Dogs; D007593:Joint Instability / Q000517:prevention & control; D007719:Knee Joint / Q000473:pathology*; D007720:Knee Prosthesis; D008422:Materials Testing; D023421:Models, Animal; D020959:Polyethylene / Q000494:pharmacology*; D019904:Polymethyl Methacrylate / Q000494:pharmacology*; D011474:Prosthesis Design; D011475:Prosthesis Failure; D012016:Reference Values; D012086:Reoperation / Q000379:methods
D001672:Biocompatible Materials; D020959:Polyethylene; D019904:Polymethyl Methacrylate