EFFECTS OF INTERMITTENT MICROMOTION VERSUS POLYMER PARTICLES ON TISSUE INGROWTH - EXPERIMENT USING A MICROMOTION CHAMBER IMPLANTED IN RABBITS

Both micromotion and particulate debris have been implicated in the pr ocess of aseptic loosening of joint arthroplasties and the failure of bone ingrowth into porous coated prostheses. In the present study, we compare the histological and histomorphometric results of tissue ingro wth into titanium chambers in the presence of interfacial micromotion versus phagocytosable particles of two polymers used in orthopedic sur gery. The micromotion chamber, having a 1 x 1 X 5 mm transverse canal for tissue ingrowth was implanted into the proximal right tibia of fiv e mature male New Zealand white rabbits. In the first series, the cham bers were manipulated at 40 cycles per day (cpd) at 1 Hz, using an amp litude of 0.5 mm. The tissue within the chamber was harvested after 3 weeks. In the following series, fabricated particles of bone cement or high-density polyethylene (HDPE) were mixed with the carrier, 1% sodi um hyaluronate (Healon) to obtain a concentration of 10(8) particles/m L; this solution was implanted in the canal of the chamber but micromo tion was not instituted. Histological sections from control, nonmoved chambers, or those implanted with the carrier Healon alone contained e xtensive trabecular and woven bone embedded in a fibrovascular stroma. The application of 40 cpd resulted in less formation of bone and more fibrous tissue within the chamber. The sections containing particles of bone cement were infiltrated by numerous foamy, mononuclear, and mu ltinuclear histiocytes. HDPE particles were associated with more fibro sis and a less aggressive foreign body response compared to cement par ticles. Chambers manipulated at 40 cpd and those containing cement or HDPE particles contained less bone compared to nonmoved chambers or th ose containing Healon alone. Despite evoking different histological re actions, the presence of micromotion or polymer particles appears to i nhibit the formation of bone in this experimental model. (C) 1994 John Wiley & Sons, Inc.