Persistent expression of mitogenic/transforming factors at the site of failed orthopaedic implants: the impact on immune reactivity.

The response to wear particles from orthopaedic implants can lead to inflammation, osteolytic lesions, and aseptic loosening. To gain an insight into the development of this pathogenetic process, immunohistochemical techniques were used to identify the expression and tissue distribution of the potent cell mitogen epidermal growth factor (EGF), and the epidermal growth factor receptor (EGF-R) at the site of bone erosion in 30 patients with clinically failed orthopaedic implants. The results showed a large proportion of the macrophage subsets (Mphi) which expressed EGF and EGF-R, also contained wear particles, indicating their expression is a consequence of Mphi phagocytosis of implant material. The surface membrane expression of EGF-R on fusing Mphi suggests its presence is fundamental to the formation of bone-resorbing multi-nucleated giant cells, and the development of osteolysis. Additionally, there is increasing evidence of the long-term systemic spread of wear particles and their accumulation at distal sites including lymph nodes, liver, and spleen. Elevated expression of mitogenic factors in response to wear particles may result in deviation from normal cell growth and regulation, resulting in changes to immune cell function. Such potential transformations at distal sites are clinically significant, as alterations to the patient's immune system may result in acute divergence from normal immune cell responses.