Die subchondrale Knochendichte am Fesselgelenk des Pferdes. Teil 2: Computertomographische Osteoabsorptiometrie (CT-OAM)

The fetlock joint (articulatio metacarpophalangea) ploys an exceptional role within the limb, as it is the only joint which is in hyperextension in the standing horse. It is therefore exposed to special loading situations compared to other joints. The objective of this study is to describe the distribution of the subchondral bone density as a measure for the longterm loading of the fetlock joint. The method of Computed Tomographic Osteoabsorptiometry (CT-OAM, Moller-Gerbi et al., 1989) was used. 45 joint preparations of the fetlock joint from 26 horses of different breeds and sizes, male and female were examined. The horses ranged from foal to 30 years of age. The joints were scanned in the sagittal plane in a CT-scanner Somatom AR(Siemens, Erlangen, Germany). Using these CT-data sets the bones of the fetlock joint were reconstructed three-dimensionally and the subchondral bone density was displayed topographically in a colour coded picture. Inthe dorso-distal aspect of the trochlea a broad transversal bond of highbone density can be observed. Palmar there are two almost triangular areas of high bone density at the trochlea. On the articular surface of the, proximal phalanx band shaped areas close to the dorsal and abaxial edges are heavily mineralized. The sesamoid bones display an average level of bone density throughout the articular facet. A relatively low bone density can be found in the dorsal and palmar part close to the border of the facet as well as in the axial area distally. This also applies to the palmar border of the phalangeal articular surface. Bone density increases significantly during growth of the animals. The density distribution of subchondral bone refers to areas of the articular surface which are exposed to extremely high loading. These are parts of the trochlea which correspond to the proximal phalanx and the proximal sesamoid bone at the angle of stance. CT-OAM is a non-invasive method, which allows the investigation of the articular longterm loading. It can be put to use in the living horse for follow-up studies after surgery or for scientific purposes.