Experimental osteoarthritis in the rabbit. II. A new method to estimate the oxygen consumption and diffusion capacity in the synovial membrane of the knee

The oxygen supply to the joint cartilage depends on the oxygen transport from the capsular arteries to the capillaries, the oxygen diffusion across the synovial membrane and the oxygen transport through the synovia. In osteoarthritis the resistance to transport across all 3 barriers may be increased because of the joint effusion, the elevated intraarticular pressure and the inflammatory changes of the synovial membrane.In the present study we describe a method to determine 2 important parameters affecting the oxygen transport through the synovial membrane: the oxygen consumption and diffusion capacity of the membrane. The principle of the method is to perfuse the joint cavity of the knee by saline saturated with air and to record the relationship between the oxygen partial pressure in the outflowing perfusate and the perfusion rate.The values found for the diffusion capacity and oxygen consumption were 0.039 ± 0.013 μl O₂/min/Torr and 0.93 ± 0.90 μl O₂/min (mean ± s).     

Oxygen consumption, diffusing capacity and blood flow of the synovial membrane in osteoarthritic rabbit knee joints

In osteoarthritis the changes of the synovial membrane may seriously alter the oxygen transfer characteristics from the capillaries of the membrane to the synovial fluid and hence impede or deprive the joint cartilage of its sole source of oxygen. In the present study we have estimated the blood flow (Q), diffusing capacity (DO2) and oxygen consumption (VO2) of the synovial membrane in the chronic non effusive stage of experimental osteoarthritis. In 14 osteoarthritic knee joints we found a statistically significant increase in oxygen consumption, compared to previously reported results from normal joints, whereas the diffusing capacity and the blood flow were unchanged. The implication of this is that the partial pressure difference required to overcome the increased oxygen consumption was increased with a factor 4.3 and that the oxygenation of the joint cartilage was reduced with approx. 30 Torr.     

Improved method to estimate oxygen consumption, diffusing capacity and blood flow of synovial membrane

The joint cartilage is depending on the oxygen diffusing from the capillaries of the synovial membrane through the synovial tissue and synovial fluid. In the present study we describe a new method to calculate the diffusing capacity (DO2), oxygen consumption (VO2) and blood flow of the synovial membrane. The principle of the method is to perfuse the joint cavity with two saline solutions, one with high and one with low oxygen and nitrogen partial pressures and to measure the oxygen and nitrogen partial pressures in the perfusate flowing out of the joint. Using a model of gas exchange between the joint and the membrane a set of equations was derived expressing the relationship between the blood flow, diffusing capacity and oxygen consumption and the oxygen and nitrogen flowing to and from the joint in the two different perfusion situations. In 12 rabbit knee joints we found a blood flow of 0.388 ml/min (SEM 0.027), VO2 of 0.495 microliters/min (SEM 0.196) and DO2 of 0.024 microliter/min/Torr SEM 0.003 (mean).     

Experimental osteoarthritis in the rabbit. I. Histological changes of the synovial membrane

Based on an experimental model of osteoarthritis in 42 full-grown rabbits the histological changes were studied during the development of osteoarthritis after operative induction of instability of the knee joint. The changes were followed from 2 week to 1½ years after the induction.The first changes were observed at 1 week stage as a proliferation of the lining cells. During the time of observation additional changes were seen such as hypertrophy of villi, infiltrations with plasma cells and lymphocytes, increased vascularity and interstitial edema and fibrosis. Edema was only seen during the first months, later increasing fibrosis was predominant.The first cartilage change was reduction of the staining ability, expressing depletion of GAG, this was seen already at the one week stage whereas morphological changes were present after 4–6 weeks.It was concluded that the synovial membrane in this model shows changes that may contribute to the development of osteoarthritis.