Pressure-induced periprosthetic osteolysis: A rat model

Recent animal experiments have indicated that oscillating fluid pressure at the interface of bone and implant can lead to osteolysis. However, externa l nonphysiologic saline solutions were used to generate the pressure in the se studies. In the present study on 15 Sprague-Dawley rats, hydrostatic pre ssure fluctuations were applied to bone through body fluids, by compressing a soft-tissue membrane adjacent to the proximal tibia. A titanium plate wa s fixed to the bone surface. After 28 days of osseointegration of the plate , a 1-mm-wide gap was created between it and the cortical bone and 5 days w ere given for fibrous tissue to form. Load was transmitted to this soft tis sue by applying force on a piston mounted in the plate. In six rats, a cycl ic pressure of 0.6 MPa was then applied to this tissue by 20 cycles twice a day with a frequency of 0.17 Hz for 5 days. The remaining rats served as c ontrols, with the piston left untouched in its upper position. All of the r ats were killed 10 days after creation of the gap. Histological sections we re produced at a right angle to the loaded surface. In the pressurized spec imens, osteoclastic bone resorption was dramatic. In all specimens, the ori ginal cortex was almost entirely resorbed but new woven bone had formed dee per in the marrow and walled off a cystic lesion. When necrotic remnants of the cortex were still in place, new woven bone was seen on the side away f rom the piston. This "lee effect" may indicate that bone formation was inhi bited by fluid now away from the pressurized tissue. The specimens with a n onloaded piston showed no signs of resorption. This new experimental model shows again that a moderate rise of hydrostatic pressure at the interface o f bone and implant leads to considerable bone resorption. This could be a m echanism of prosthetic loosening.