Adverse reaction to metal debris (ARMD) is well recognised as a complication of large head metal on metal total hip replacement (THR) leading to pain, bone and tissue loss and the need for revision surgery. An emerging problem of trunnionosis in metal on polyethylene total hip replacements leading to ARMD has been reported in a few cases. Increased metal ion levels have been reported in THR's with a titanium stem and a cobalt chrome head such as the Accolade-Trident THR (Stryker).

We present 3 cases of ARMD with Accloade-Trident THR's with 36mm cobalt chrome head and a polyethylene liner. Metal ion levels were elevated in all three patients (cobalt 10.3 – 161nmol/l). Intraoperative tissue samples were negative for infection and inflammatory markers were normal. Abnormal fluid collections were seen in all three cases and bone loss was severe in one patient leading to a proximal femoral replacement. Histology demonstrated either a non-specific inflammatory reaction in a case which presented early or a granulomatous reaction in a more advanced case suggesting a local foreign body reaction. All patients had improved symptoms post-operatively. 1 patient who had staged bilateral Accolade-Trident THR's required revision of both THR's.

ARMD in metal on polyethylene THR's with a titanium stem represents a potential emerging problem. Further studies are required to assess whether these occurrences are rare or represent the tip of an iceberg.

Human mesenchymal stem cells (hMSCs) have the capacity to differentiate into adipocytes, chondrocytes, or osteoblasts, and are an exciting tool to be used in regenerative medicine and surgery. By manipulating the surface structure and physical properties of a biomaterial on which hMSCs can be incorporated, the biological response of these cells at the implant site can be controlled. Whilst both topography and surface stiffness are known to influence differentiation of hMSC's, little is understood of the molecular mechanisms that underpin these responses. In this study we use immunofluorescence and confocal microscopy techniques to assess the change in both the abundance and the distribution of H3K9me2 or H3K9ac patterns in hMSCs cultured on materials with controlled topography and stiffness, under basal and osteogenic conditions. These data demonstrate that levels and localisation of both H3K9me2 and H3K9ac alter in hMSCs cultured on the different substrates and that these surfaces dictate the response to osteogenic stimuli, suggesting that the control of cytoskeletal structure can be linked to chromatin activity. This regulation of histone modification by MSC interaction with the surrounding scaffold provides not only a mechanistic link to the control of cell fate but also the opportunity to design biomaterials that better influence cell activity.