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Kaiser, Annette (2006): Morphologische und biomechanische Eigenschaften des Karpalgelenks (Articulatio carpi) des Hundes (Canis familiaris). Dissertation, LMU München: Faculty of Veterinary Medicine
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Abstract

The objective of this study was to investigate anatomical and biomechanical parameters of the canine capal joint in order to determine the physiological situation of articular loading. 121 carpal joints of 61 dogs of varying age weighing more than 20 kg were examined. The joint angle of the carpal joint was measured in 50 standing dogs. Long term tensile stresses of the articular cartilage and the subchondral bone were determined by the split line method. The distal articular surface of the radius showed two different types of split line patterns, a clear transverse orientation or one singular attractive point at the dorsal rim of the articular surface. The split lines at the dorsal aspect of the radius diverged towards its distal end, which is an evidence of a transverse strain of the articular surface during loading. In all joints compressively loaded regions were located especially in the dorsal parts of the articular surfaces. The articular surfaces of the second carpal bone showed two different split line patterns depending on the weight of the dogs. The palmar aspects of the proximal articular surfaces of the metacarpal bones showed evident transverse tensile stress. The silicon cast method was used to determine the contact areas and Fuji pressure sensitive film to determine the contact pressures at different loading steps. In all joints of the carpus the contact areas increased nonlinear with an increasing loading rate. They never included more than 50% of the convexe articular surface. Contact areas in the antebrachiocarpal joint always were larger than those of the midcarpal and carpometacarpal joint at the same loading step, the latter being nearly identical for each loading step. Because of the hyperextension the antebrachiocarpal contact areas were located close to the dorsal edge of the articular surfaces, while in the midcarpal and carpometacarpal joint they reached further palmar. The centres of the contact pressures corresponded closely with the centres of the contact areas. Greater pressures in the antebrachiocarpal joint were located medially, in the midcarpal joint they were equally distributed over the whole articular surface, while in the carpometacarpal joint they were found laterally. The long term loading situation of the articular surfaces was investigated by means of computertomography-osteoabsorptiometry (CTOAM). Individual CT-datasets were matched onto one target joint surface. Thus the mean values of all bone density measurements of the subchondral bone could be visualized. Areas of high bone density were very consistent and coincided with the location of high compressive load in the split line investigation and the contact areas. In the antebrachiocarpal joint, areas with high bone density were found dorsomedially. In both the midcarpal and carpometacarpal joint they were more equally distributed over the joint surfaces. With increasing age the subchondral bone density increases as well. Furthermore the bone density maxima are more clearly demarcated in older animals. The joint angle of the carpal joint of standing dogs showed a significant correlation with the age of the animals. Body weight and breed did not have any influence. From the biomechanical point of view the distal radioulnar ligament is a tensile loaded structure which connects radius and ulna distally and inhibits a separation of the two bones in stress. Moreover it increases the congruence of the antebrachiocarpal joint and thus is stressed with compressive forces. Because of the physiologic hyperextension and valgus-angulation of the carpal joint the articulation with the greatest range of motion, the antebrachiocarpal joint, is loaded unilaterally. Due to the limited range of motion in both the midcarpal and carpometacarpal joint the load is equally distributed over the articular surface in these two joints.