Effect of PMMA particles and movement on an implant interface in a canine model

The pathogenesis of aseptic loosening of total joint prostheses is not clea rly understood, Two features are associated with loosened prostheses, namel y, particulate debris and movement of the implant. While numerous studies h ave evaluated the cellular response to particulate biomaterials, few have i nvestigated the influence of movement of the implant on the biological resp onse to particles. Our aim was therefore to test the hypothesis that excess ive mechanical stimulation of the periprosthetic tissues induces an inflamm atory response and that the addition of particulate biomaterials intensifie s this. We allocated 66 adult Beagle dogs to four groups as follows: stable implant s with (I) and without (II) particulate polymethylmethacrylate (PMMA) and m oving implants with (III) and without (IV) particulate PMMA, They were then evaluated at 2, 4, 6, 12 and 24 weeks. The stable implants were well tolerated and a thin, fibrous membrane of con nective tissue was observed. There was evidence of positive staining in som e cells for interleukin-6 (IL-6), Addition of particulate PMMA around the s table implants resulted in an increase in the fibroblastic response and pos itive staining for IL-6 and tumour necrosis factor-alpha (TNF-alpha). By co ntrast, movement of the implant resulted in an immediate inflammatory respo nse characterised by large numbers of histiocytes and cytokine staining for IL-1 beta, TNF-alpha and IL-6, Introduction of particulate PMMA aggravated this response. Animals with particulate PMMA and movement of the implant h ave an intense inflammatory response associated with accelerated bone loss. Our results indicate that the initiation of the inflammatory response to bi omaterial particles was much slower than that to gross mechanical instabili ty. Furthermore, when there was both particulate debris and movement, there was an amplification of the adverse tissue response as evidenced by the pr esence of osteolysis and increases in the presence of inflammatory cells an d their associated cytokines.