The effects of bulk versus particulate ultra-high-molecular-weight polyethylene on bone.

Fourteen mature New Zealand white female rabbits underwent implantation of a bulk pellet and of particulate (less than 1,000 micron) ultra-high-molecular-weight polyethylene (UHMWPE), through a drill hole in the proximal right tibia. The left tibia served as a drilled but nonimplanted control. The rabbits were killed after 16 weeks. Histologic examination of the bone-implant interface in the bulk UHMWPE group disclosed a fibrous tissue membrane with infrequent giant cell and histiocytic clusters at surface irregularities. The particulate group demonstrated positively birefringent UHMWPE fragments, rimmed by foreign body giant cells and histiocytes, embedded in a loose connective tissue. The histologic response to particulate UHMWPE is similar to that seen surrounding loose total joint arthroplasties in humans.