Purpose: Restoration and maintenance of the plateau surface are the key points in the treatment of tibial plateau fractures. Any deformity of the articular surface jeopardizes the future of the knee by causing osteoarthritis and axis deviation. The purpose of this study is to evaluate the effect of trabecular metal (porous tantalum metal) on stability and strength of fracture repair in the central depression tibial plateau fracture.

Method: Six matched pairs of fresh frozen human cadaveric tibias were fractured and randomly assigned to be treated with either the standard of treatment (impacted cancellous bone graft stabilized by two 4.5mm screws under the comminuted articular surface) or the experimental method (the same screws supporting a 2 cm diameter Trabecular Metal (TM) disc placed under the comminuted articular surface). Each tibia was tested on a MTS machine simulating immediate postoperative load transmission with 500 Newton for 10000 cycles and then loaded to failure to determine the ultimate strength of the construct. Results: The trabecular metal construct showed 40% less caudad displacement of the articular surface (1, 32 ±0.1 mm vs. 0, 80 ±0.1 mm) in cyclic loading (p< 0.05). Its mechanical failure occurred at a mean of 3275 N compared to 2650 N for the standard of care construct (p< 0, 05).

Conclusion: The current study shows the biomechanical superiority of the trabecular metal construct compared to the current standard of treatment with regards to both its resistance to caudad displacement of the articular surface in cyclic loading and its strength at load to failure.

Although the response of macrophages to polyethylene debris has been widely studied, it has never been compared with the cellular response to ceramic debris. Our aim was to investigate the cytotoxicity of ceramic particles (Al₂O₃ and ZrO₂) and to analyse their ability to stimulate the release of inflammatory mediators compared with that of high-density polyethylene particles (HDP). We analysed the effects of particle size, concentration and composition using an in vitro model. The J774 mouse macrophage cell line was exposed to commercial particles in the phagocytosable range (up to 4.5 μm). Al₂O₃ was compared with ZrO₂ at 0.6 μm and with HDP at 4.5 μm. Cytotoxicity tests were performed using flow cytometry and macrophage cytokine release was measured by ELISA.

Cell mortality increased with the size and concentration of Al₂O₃ particles. When comparing Al₂O₃ and ZrO₂ at 0.6 μm, we did not detect any significant difference at the concentrations analysed (up to 2500 particles per macrophage), and mortality remained very low (less than 10%). Release of TNF-α also increased with the size and concentration of Al₂O₃ particles, reaching 195% of control (165 pg/ml v 84 pg/ml) at 2.4 μm and 350 particles per cell (p < 0.05). Release of TNF-α was higher with HDP than with Al₂O₃ particles at 4.5 μm. However, we did not detect any significant difference in the release of TNF-α between Al₂O₃ and ZrO₂ at 0.6 μm (p > 0.05). We saw no evidence of release of interleukin-1α or interleukin-1ß after exposure to ceramic or HDP particles.

We made a semiquantitative study of the comparative histology of pseudomembranes from 12 loose cemented ceramic-ceramic and 18 metal-polyethylene total hip replacements. We found no significant difference in cellular reaction between the two groups, but there was a major difference in the origin of the particulate debris. In the metal-polyethylene group, polyethylene of articular origin was predominant, while in the ceramic-ceramic group the cellular reaction appeared to be a response to zirconia ceramic particles used to opacify cement used for fixation.

Isolation and characterisation of the debris showed that the zirconia particles formed the greatest proportion (76%) in ceramic-ceramic hips, while alumina debris of articular origin formed only 12%.

Our study has indicated that aseptic loosening of ceramic cups is not due to a response to debris generated at the articular interface, but to mechanical factors which lead to fragmentation of the cement.