Periprosthetic osteolysis depends on the biological activity of wear particles, but there is little known about the distribution of polyethylene wear particles (PE) in the surrounding joint tissue. The purpose of this study was to examine the localisation of wear particles of six different PEs, including four crosslinked polyethylenes (XPE), as well as their biological activity in the murine knee. Wear particles of 4 XPE- and 2 UHMWPE-inserts were isolated (knee joint simulator). For all groups the particles were similar in size and shape (mean diameter 0.3–05μm; 20nm-nucleopore-filter; ISO; n = 100.000).56 female Balb/c mice were randomly assigned to six treatment groups and one control group: control (PBS), XPE1 (3×30 kGy Gamma, annealed/sequential irradiated), XPE2 (95 kGy E-beam, remelted), XPE3 (65 kGy E-beam, remelted), XPE 4 (50 kGy Gamma, remelted), UHMWPE 1, UHMWPE 2. 50 μl of each particle suspension [(0.1% vol/vol (particle volume/PBS volume) after removal of endotoxin] were injected into the left knee joint. After 1 week the mice were killed and a histological and immunhistochemical analysis of the knee joints was done (IL-1, TNF-, ICAM-1). For the immunhistochemistry the articular cartilage, the bone marrow and the synovial membrane were evaluated semiquantitatively (Kruskal-Wallis test; all pairwise multiple comparison procedure; Bonferoni correction; significance level: p<0.05). All groups showed a thickened synovial layer with an increased cellular infiltration. The particles of XPE 1 and 2 were localised in the bone marrow as well as in the joint space. In contrast, the particles of XPE 3 and 4 were distributed in the synovial layer and in the bone marrow as well, but not in the joint space. The UHMWPE1 particles were mainly located in the bone marrow and joint space while the UHMWPE2 particles were mainly found in the bone marrow and the synovial layer. For all PE groups there was a higher cytokine expression compaired to control (p<0.0024) without any differences between the groups (bone marrow/synovial layer). The chondrocytes in the groups with XPE 1- and XPE 2-particles expressed more TNF- than in the control group and the other treatment groups (p = 0.000).Material and Methods
Results
Crosslinked polyethylene (XPE) was developed to reduce wear in hip and knee arthroplasty. Periprosthetic osteolysis depends on many factors including biological activity of wear particles. This study examines the relative inflammatory effect of different crosslinked polyethylenes compared to ultra-high-molecular-weight-polyethylene (UHMWPE) particles in vivo.
40 female Balb/c mice were randomly assigned to one of five treatment groups (according to the national guidelines of animal protection laws): control (n=8); XPE1 (95 kGy E-beam, remelted; n=8); XPE2 (65 kGy E-beam, remelted; n=8), XPE3 (3x30 kGy Gamma, annealed and sequential irradiated; n=8) and UHMWPE particles (n=8). 50 μl of the particle suspension were injected into the murine left knee under sterile conditions. The leukocyte–endothelial cell interactions and the synovial microcirculation were performed by intra-vital fluorescence microscopy one week after particle injection to assess the inflammatory reaction to the particles (by measuring the rolling fraction of leukocytes, the adherent cells and the functional capillary density (FCD)). Data analysis was performed using a computer-assisted microcirculation analysis system (Cap-Image). For the statistical analysis the Kruskal-Wallis test was used to determine differences within the groups, followed by an all pairwise multiple comparison procedure with a Bonferoni correction. The level of significance was set at p<
0.05.
