Morphologische und biomechanische Eigenschaften des Hüftgelenks (Articulatio coxae) des Hundes (Canis familiaris)
Morphological and biomechanical characteristics of the canine hip joint (articulatio coxae) Morphological and biomechanical parameters of the canine hip joint have been investigated for the first time in order to determine the long term loading of the hip joint surfaces. 86 hip joints of 43 predominantly large breed dogs (average age 6 years) were examined. By means of CT-osteoabsorptiometry (CT-OAM) the subchondral bone density was determined qualitatively and quantitatively. The exact topographic distribution of the subchondral bone density was shown in three-dimensional reconstructions of the hip joints in false colour code. The distribution pattern was regularly tricentric with bone density maxima located in the cranial and caudal aspects of the joint surfaces as well as in the roof of the acetabulum and the perifoveal area of the caput ossis femoris. The anteversion of the Os femoris was determined by a computed tomographical method. The findings allowed the assumption of a causal relationship between a reduced anteversion angle and a shift of the density maxima to the medial part of the joint surface of the caput ossis femoris. The main direction of the collagen fibres in the joint cartilage and the subchondral bone were traced by means of the split line method. The split line pattern established proof of an existing tension and bending in the acetabulum. Moreover it identified areas of compressive stress on the surface of the joint (cranial and caudal aspect of the lunate surface and the femoral head). Biomechanical parameters such as contact areas as well as distribution and amount of pressure were determined experimentally under physiological load conditions representing the three leg stance during slow walking. These data were gained by casting material and pressure sensitive film. At low loads and physiological angulation contact areas were mainly found at the peripheral margin of the cranial and caudal part of the facies lunata and caput ossis femoris. At the cranial roof of the acetabulum a joint space was evident in the loaded specimens up to 75% body weight. Under increasing loads the contact areas expanded towards the joint centre. The maximal contact pressure ranged from 8 to10 MPa under a load of 400% body weight. Areas of load transfer showed a more obvious bi- and tricentric distribution pattern than contact areas. With increasing loads areas of load transfer expanded to a uniform area. The results of this study established proof of the inhomogeneous load distribution in the canine hip joint. For the first time it was shown that the canine hip joint is not congruous as commonly assumed but maintains a physiological incongruity. This guarantees for an optimal load distribution in the joint and for a better nutrition of the joint cartilage. Further, it was shown that osteoarthrosis more often exists in those areas of inhomogeneously loaded joint surfaces which are exposed to larger mechanical stress a priori.
Networked Digital Library of Theses and Dissertations