Comparison of UHMWPE particles in synovial fluid and tissues from failed THA

The size and morphology of ultra high molecular weight polyethylene (UHMWPE) wear particles isolated from synovial fluid and periprosthetic tissues from three failed total hip arthroplasties were evaluated. Hip capsule, femoral canal tissue, and synovial fluid were collected at the time of revision surgery. The polyethylene wear particles were isolated and then imaged using a scanning electron microscope. The size and morphology of the particles were quantified using an image analysis protocol. Five shape descriptors were defined for each particle: equivalent circle diameter (ECD, a measure of size having units of length), aspect ratio (AR), elongation (E), roundness (R), and form factor (FF). The size and shape of the polyethylene particles differed depending on the source. Femoral tissue particles had the lowest equivalent circle diameter (0.697 +/- 0.009 mm), aspect ratio (1.577 +/- 0.016), and elongation (1.912 +/- 0.030), but the highest values for roundness (0.715 +/- 0.005) and form factor (0.874 +/- 0.003). Hip capsule particles had the highest equivalent circle diameter (0.914 +/- 0.019 mm), aspect ratio (1.764 +/- 0.025), and elongation (2.488 +/- 0.053), but the lowest values for roundness (0.642 +/- 0.006) and form factor (0.803 +/- 0.005). The size and shape descriptors for synovial fluid particles (equivalent circle diameter: 0.763 +/- 0.012 mm; aspect ratio: 1.700 +/- 0.029; elongation: 2.212 +/- 0.054; roundness: 0.681 +/- 0.006; and form factor: 0.841 +/- 0.004) were intermediate among the femoral tissue and hip capsule particles. These data suggest that larger particles may become lodged in the hip capsule, while smaller particles may migrate to more distant tissues and subsequently cause aseptic loosening and osteolysis.