A 45 year old female underwent limb salvage surgery for osteosarcoma of distal end of femur in 2004. a custom made prosthesis made of titanium was inserted after successful resction of the tumour. In october 2009 she sustained injury to the previously operated thigh. An x-ray revealed broken prosthesis at the junction of body and femoral stem (fig 1).
Revision of custom made prosthesis was undertakne. At surgery the synovial lining was found to be grossly hypertrophied and showed extensive black discoloration (fig 2).
The abnormal tissue was excised and submitted for histology. the synovial aspect of the joint capsule showed a marked vilous surface with a grey-black colour, which extended to the superficial parts of the tissues upto the proximal part of previously excised femur. The underlying connective tissue of the joint capsule appeared normal. the patient underwent a successful revision with a fresh custom built prosthesis (fig 3).
Histology showed accumulation of particular black pigmented metallic fragments in histocytes and in synoviocytes (fig 4). There was uniform spread of titanium particles. the clinical and histological picture was suggestive of Metallosis discussion
Prostheses have an established role in articular replacement but may fail due to wear with loosening. To prevent this complication metal-on-metal prostheses have been developed which are expected to perform better. Metallosis refers to the presence of metal particles in tissue, which are derived from prosthetic implants, which fail due to wear of polyproplene insert . The metal accumulates in histiocytes and synovial cells and may even be transported to regional lymph nodes. Metallosis may be severe in metal-on-metal prosthesis and may be particularly pronounced in cases with incompatible metal combinations. It is less common in metal-on-polyethylene devices. Titanium metal particles liberated from prosthetic joints are essentially inert. Low grade inflammation is seen in soft tissues surrounding wearing joint prosthesis but whether this is due to the metal particles in not clear. Other metals frequently used in joint prosthesis are chromium., cobalt and stainless steel. although animal model experiments have shown that these metal may induce an inflammatory response the biological effets in humans are not clear. Microsopic metal fragments which vary insize, may accumulate intra-cellular in macrophages or in extra-cellular tissue components. the type of metal cannot be determined by light microscopy, for this determination EDX anlaysis is required the extensive fibrosis may result in pseudo-tumourus appearance of which the name metalloma or titanoma has been suggested. the polyethylene inlay with which the metal component articulates likewise wears with liberation of irregular fragments. these particles are taken by macrophages and evoke giant-cell formation and fibrosis.