抄録
Purpose : The main function of the articular cartilage is to disperse the burden on the joint and, with minimum friction and wearing, allow relative movement with the facing joint. In our experiment, in order to examine the characteristics of cartilage, an external force was applied to a point on the cartilage surface and the effects on the surrounding cartilage were chronologically assessed.
Materials and Methods : Twenty samples were taken from the articular cartilages of frozen (at-70°C) femoral heads of adult bovines of approximately four years of age and one ton in weight. Cartilage samples were gathered from the subchondral bone of the loaded area of the femur. Observations were made while the samples were immersed in a physiological solution.
A probe with a diameter of 1.5mm was used to add a fixed load of 0.59N to the sample's surface for 10 minutes. During the loading period, the area of deformation occurring on the cartilage surface was continuously observed by real-time holographic interferometry. At the same time, the depth of the concavity produced on the cartilage was determined with a laser displacement sensor.
Using a microcomputer to generate output from the laser displacement sensor, the AD change was reproduced and video signals were established for recording, Stress-strain curves were registered on the screen. The reproduction images were printed out and the area of modification to the cartilage was measured with a digitizer. The altered deformation of the cartilage was thus represented three-dimensionally.
Results and Discussion : Holographic interferometry revealed concentric interference circles around the loaded point of the cartilage and showed that concave deformation occurred in the surrounding area of the cartilage. The effect of the force immediately spread in a concentric manner around the loaded point. With time, the area around the loaded point (that not directly loaded) showed a gradual recovery from the initial deformation. Approximately five minutes after the commencement of loading, the changes roughly reached a balanced state. After the load was removed, the deformation immediately extended to a wider arc for several seconds, but both the concave deformation at the loaded point and the deformation in the surrounding region recovered with time. Holographic observation showed that the greatest change in concave deformation occurred not within 0.5 seconds after the load was added, but rather immediately after the load was removed. Thus a considerably wide-spread concave deformation was observed on the cartilage surface for a short period after application and after the removal of the force on the cartilage. This change seems to represent the visco-elastic properties of the cartilage that enable an abrupt change in the load (caused by a sudden application of external force) to be dispersed in a short time into the bone below the cartilage.
