The influence of activity upon the structure and properties of articular cartilage has been examined in two populations of fur-bearing animals. Morphological changes in cartilage of the caged animals were noted. Friction was mentioned in a vibrotribometer and it was noted that the caged animals exhibited a lower friction coefficient than the free-moving animals. In both cases the friction initially increased with age, reaching a maximum after about three years. It is concluded that prolonged hypokinesis associated with a cage-breeding regime acts like a mechanical stress factor which stimulates the development of degenerative changes in cartilage.

This paper gives a short description of the lubricating properties of yellow and red bone marrow taken from a femur of a cadaver. The experiments have been conducted on a 'ball-on-plate' model. The balls were made from steel 100 CR6 (German) and the plates were made from the same steel and ultra-high molecular weight polyethylene (UHMWPE, German 'Herulen'). The friction coefficients under loads of 50 and 300 N were determined with different combinations of friction components. It has been found that the lubricating properties of yellow and red marrow have advantages over synovial fluid. In the light of these results the author develops a new approach to the design of a new hip endoprosthesis.