Effects of intermittent micromotion versus polymer particles on tissue ingrowth: Experiment using a micromotion chamber implanted in rabbits

Abstract

AbstractBoth micromotion and particulate debris have been implicated in the process 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 ingrowth into titanium chambers in the presence of interfacial micromotion versus phagocytosable particles of two polymers used in orthopedic surgery. The micromotion chamber, having a 1 × 1 × 5 mm transverse canal for tissue ingrowth was implanted into the proximal right tibia of five mature male New Zealand white rabbits. In the first series, the chambers were manipulated at 40 cycles per day (cpd) at 1 Hz, using an amplitude of 0.5 mm. The tissue within the chamber was harvested after 3 weeks. In the following series, fabricated particles of bone cement or highdensity polyethylene (HDPE) were mixed with the carrier, 1% sodium hyaluronate (Healon) to obtain a concentration of 108 particles/mL; this solution was implanted in the canal of the chamber but micromotion was not instituted. Histological sections from control, nonmoved chambers, or those implanted with the carrier Healon alone contained extensive 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 multinuclear histiocytes. HDPE particles were associated with more fibrosis and a less aggressive foreign body response compared to cement particles. Chambers manipulated at 40 cpd and those containing cement or HDPE particles contained less bone compared to nonmoved chambers or those containing Healon alone. Despite evoking different histological reactions, the presence of micromotion or polymer particles appears to inhibit the formation of bone in this experimental model. © 1994 John Wiley & Sons, Inc.