Intraosseous pressure in the patella in relation to simulated joint effusion and knee position: an experimental study in puppies.

Simultaneous pressure measurements were carried out in the patella, juxtaarticular epiphyses and the knee joint cavity of six mongrel puppies. The mean intraosseous pressure in the patella was 12.2 mmHg, range 8-15 mmHg. An increase in intraarticular pressure in turn caused an increase in the intraosseous pressure of the patella and juxtaarticular epiphyses. The pressure increase in the patella was the most pronounced. During extension of the knee joint, a significant rise in intraosseous pressure of the tibial epiphysis and patella was observed, whereas during flexion femoral epiphyseal pressure and patellar pressure increased significantly. The introduction of moderate intraarticular effusion amplified intraosseous pressure responses during flexion of the knee joint. The intraosseous pressure changes during knee movement could not be explained solely by the corresponding changes in intraarticular pressure. Intraosseous phlebography revealed a venous drainage system largely parallel to the arterial blood supply. The contrast clearance time was decreased during moderate elevation of the intraarticular pressure, suggesting increased bone blood flow of the patella.