Total joint arthroplasty is one of the success stories of modern surgery, providing dramatic pain relief and improved joint function for patients with arthritic disease. However, periprosthetic bone resorption and aseptic loosening of joint implants is becoming recognised increasingly as a major cause of failure of cemented and uncemented arthroplasties. Implant-derived biomaterial wear particles are generated from joint implant components; these particles are deposited in periprosthetic tissues where they are taken up by macrophages.
Nick Athanasou and Afsie Sabokbar at the Nuffield Department of Orthopaedic Surgery are using a recently developed in vitro method of generating human osteoclasts from blood monocytes and tissue macrophage population. They have shown that macrophages containing wear particles, isolated from periprosthetic tissue surrounding loose implants are capable of differentiating into osteoclasts, specialised bone-resorbing cells. It has also been shown that human monocytes that have phagocytosed wear particles are capable of osteoclast formation and bone resorption. Macrophages responding to particles of some implant materials (e.g. acrylic bone cement containing the radio-opaque barium sulphate) show an increased ability to undergo osteoclast differentiation.
Macrophages in periprosthetic tissues have also been found to provide all the factors required for such osteoclast formation. These findings point to a major role for the cellular response to implant-derived biomaterial wear particles in causing the periprosthetic bone resorption associated with aseptic loosening.
Current research aims to further basic understanding of bone resorption and its role in aseptic loosening.
Lacunar pit formed by a particle containing osteoclast. "P" is a lacunar pit, "L"is a latex particle.