A controlled experimental model of revision implants: Part I. Development

Abstract

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 m m 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 poly ethylene (0.5-12 m m), and type B particulate polyethylene (0.5-50 m m; 85% < 12 m m). 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 brous 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 brous connective tissue. The model creates a revision cavity analogous to that seen in revision joint arthroplasty, and merits further studies of revision joint replacement.n

Aseptic loosening, not only a question of wear: A review of different theories

“…However, as shown in Table, the amounts and sizes of particles have varied between the different studies (Howie et al 1988, Goodman 1994, Bobyn et al 1995, Dowd et al 1995, Frökjaer et al 1995, Goodman et al 1995, 1999, Kraemer et al 1995, Allen et al 1996, Aspenberg and Herbertsson 1996, Shanbhag et al 1997, Van Der Vis et al 1997, Kim et al 1998, Frökjaer et al 1999, Lalor et al 1999, Brooks et al 2000, Rahbek et al 2000, 2001, Bechtold et al 2001, Bi et al 2001b, Sundfeldt et al 2002. The time of introduction of the particles and the design of the studies also varied greatly.…”

Do Bone Graft and Cracking of the Sclerotic Cavity Improve Fixation of Titanium and Hydroxyapatite-coated Revision Implants in an Animal Model?

“…The model represents a cancellous environment such as the proximal metaphyseal region of a stemmed component but does not attempt to recreate the complexity of a human revision setting and bone bed (bone loss, medialization or shortening, and loss of structural competence of remaining bone) [15,20,24]. The revision protocol in this animal model uses a bilateral loaded implant, pistoning in the presence of polyethylene particles, and presents at revision with features characterizing loosened human implants [3,4]. Although the protocol does not include structural aspects related to bone loss such as a patulous canal at revision surgery, the level of experimental control on conditions at the local bone-implant interface and the ability to conduct within-animal comparisons importantly improve reproducibility.…”

“…Under approval from the Minneapolis Medical Research Foundation Institutional Animal Care and Use Committee (Protocol 01-17), we implemented our contralateral/paired controlled revision protocol [3,4] in two separate groups of female canines (Table 1). One group received bilateral cylindrical Ti6Al4V implants in the distal femur (mean weight 23 kg, range 20-27 kg, mean age 15 months, n = 8).…”

“…Mechanical axial pushout tests (5.0 mm/min) were performed on the 3-mm transverse fresh frozen implant/bone sections (MTS Mini Bionix 858, Eden Prairie, MN, USA) [3,4]. Ultimate shear strength, apparent shear stiffness, and energy absorption to failure were derived from force-displacement curves using nominal data from individual implant diameters and specimen thicknesses.…”

“…In a series of animal studies, we have tried to determine how the surgeon should approach the sclerotic bone shell to stimulate bone ingrowth and improve revision implant fixation. We introduced a surgical technique that cracks (perforates) through the sclerotic bone shell without damaging the cortex and that maintains the integrity of the long bone (''crack'' revision technique) [3,4,12]. The goal for this technique was to disrupt the physical bone barrier (sclerotic shell) and to allow marrow and vascular elements to access the revision implant surface, thereby enhancing bone ingrowth.…”