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.