Elastase activity, uninhibited by alpha 1-antitrypsin, in the periprosthetic connective matrix around loose total hip prostheses

Polyethylene wear particles do not induce inflammation or gelatinase (MMP-2 and MMP-9) activity in fibrous tissue interfaces of loosening total hip arthroplasties

In vitro and in vivo studies have suggested that polyethylene wear particles are the main cause for osteolysis in prosthetic loosening. Elevated amounts of proteases including gelatinases (or matrix metalloproteinases MMP-2 and MMP-9) have been found in fibrous tissue interfaces of loosened total hip arthroplasties suggesting that proteolysis plays a role in osteolysis. The presence of proteases does not mean that they are active, because activity of proteases is highly regulated at the post-translational level. We investigated whether the activity of two major proteases that are active extracellularly and have been associated with loosening, MMP-2 and MMP-9, is involved in loosening of non-cemented hip implants with polyethylene acetabular components. Eight interface tissues retrieved during revision were studied with light and electron microscopy and by in situ zymography to localize MMP-2 and MMP-9 activity in combination with immunohistochemistry to localize MMP-2 and MMP-9 proteins. All interface tissues contained large amounts of polyethylene wear particles, either in large accumulations or dispersed in the extracellular matrix or intracellularly in fibroblasts. Particles were not encountered in association with MMP-2 or MMP-9 activity or leukocytes. Inflammation was never found. MMP-9 activity was restricted to macrophages and MMP-2 activity was restricted to microvascular endothelial cells mainly outside areas where particles were present. Our data indicate that wear particles do not induce activation of leukocytes or MMP-2 or MMP-9 activity. Therefore, aseptic loosening may not be particle induced but initiated by other mechanisms such as mechanical stress.

Wear particulate and osteolysis

Total joint replacements of the hip and knee are generally highly successful, with satisfactory longevity and clinical results. Using modern biocompatible materials, optimal component design, and meticulous surgical technique, survivorship of cemented or cementless joint replacements is approximately 15 years with more than a 90% probability. The host's biologic response is critical to implant longevity. Particulate disease refers to the host's adverse biologic response to wear debris and byproducts generated from the prosthesis. Initially, emphasis was placed on particulate polymethylmethacrylate (cement disease), but more recently polyethylene wear debris has been underscored. Debris from several materials in sufficient quantities and physicochemical forms, however, can generate an inflammatory cascade resulting in periprosthetic bone destruction (osteolysis), jeopardizing long-term success of the implant.

Serum levels of interleukin 6 (IL-6), granulocyte-macrophage colony-stimulating factor (GM-CSF) and elastase in aseptic prosthetic loosening

In synovial-like membranes from failed total hip prostheses, an increased level of cytokines and cellular mediators has been identified. We compared two matched groups of patients with total hip arthroplasty (THA)--one with surgically proven component loosening and one without. We measured serum levels of interleukin 6 (IL-6), granulocyte-macrophage colony-stimulating factor (GM-CSF) and elastase. Soluble interleukin 2 receptor (sIL-2r) was also measured to exclude any hypersensitivity reaction. We found no significant difference in serum values between groups. Neither were there any differences with respect to implant material, mode of fixation, and periprosthetic osteolysis. In contrast to previous reports, our results suggest that serum levels of cytokines and cellular mediators may not be affected in aseptic loosening.

Immunohistochemical evaluation of interface membranes from failed cemented and uncemented acetabular components

Aseptic loosening of acetabular components is a primary factor compromising the long-term outcome of cemented and cementless total hip replacement. It is unknown whether the pathogenesis of the loosening process is identical for both types of fixation. The specific aim of this study was to determine whether there is a difference in the cellular and cytokine profiles of interface membranes removed from between the implant and the host bone from failed cemented (n = 5) and failed cementless acetabulae (n = 5). Routine histology and immunohistochemical evaluations were completed on each tissue specimen. The monoclonal antibodies used included those specific for cell types (macrophages, fibroblasts, T lymphocytes) and for cytokines (IL-1beta, IL-6, TNF-alpha). The patients were all revised for loosening. The time to revision was significantly longer for the cemented group (16.6 yr; 13-21 range) than for the cementless group (8.9 yr; 4-13 range). In all cases, slides from each group stained positively for each of the cell types and cytokines evaluated. Immunohistochemical analyses indicated a predominance of macrophages and ubiquitous staining for the cytokines IL-1beta and TNF-alpha within the membranes of both patient groups. The intensities of cytokine staining were similar for both patient groups. More regions of fibroblastic connective tissue were observed surrounding failed cementless components as compared to those of the cemented group. The clinical ramification of our findings is that, despite differences in the cellular composition of the periprosthetic membranes, the membranes from failed cemented and cementless implants contain cytokines, which have been shown to be capable of modulating the inflammatory response. These inflammatory mediators are likely to play a significant role in the development of osteolysis and prosthetic loosening.