Short periods of oscillating fluid pressure directed at a titanium-bone interface in rabbits lead to bone lysis

Fluctuating high fluid pressures have been reported in pseudojoints after total hip arthroplasty, and may be present throughout the effective joint space. When the pressure extends locally to the bone implant interface, we hypothesized that it might have led to bone resorption. We developed an experimental implant model to study whether oscillating fluid pressure, applied during 2 hours a day, can lead to osteolysis at the bone implant interface. 12 mature rabbits received a titanium implant, which was allowed to osseointegrate. Thereafter, fluid pressure was applied to a specific area of the titanium bone interface at the periosteal side of the cortex in 6 of the rabbits. The pressure, applied during 2 hours a day for 14 days, oscillated between 70 and 150 mm Hg, with a frequency of 0.1 Hz. Bone resorption was not found in any of the control animals, but it occurred under 4 implants exposed to fluid pressure (p = 0.03; Fisher's exact test). Localized osteolytic lesions had developed, with evidence of osteocyte death in the surrounding cortical bone. In 1 of the 2 specimens without osteolysis, there was evidence of fluid leakage into the soft tissues. In 4 specimens (3 with and 1 without osteolysis), bone formation was observed at the endosteal side opposite to the pressure zone. This did not occur in the controls. No signs of infection were observed. Our findings indicate that oscillating fluid pressure, even when present only during short periods, can lead to osteolysis and may be a cause of prosthetic loosening. Endosteal bone apposition may be a result of the interstitial flow that was created, giving false signals of mechanical load to the osteocytes.