Hydraulic resistance in bones of the canine shoulder

The hydraulic properties of trabecular bone were explored in both sides of normal canine shoulders by following the hydrostatic pressure response to transchondral injections of saline. In a series of isovolumetric injections at sites 9 mm beneath either joint surface, the pressure consistently rose higher and lasted longer in the humerus than it did in the scapula. Hydraulic resistance, the linear function of pressure per unit flow, averaged 8.8 times higher within the humerus than in the scapula in a second series of experiments. Hydraulic resistance fell by average factors of 9.6 in the humerus and 4.3 in the scapula when the surrounding bone was cut away to leave the injection site centered within a 1 cm 'cube' of trabecular bone. Direct determinations of hydraulic resistance provide a useful tool for the study of normal and abnormal physiology in trabecular bone.