Nitrogen Metabolism After Fracture

Abstract

AFTER a severe injury, such as a fracture, nitrogen balance usually becomes negative and the body loses nitrogen. The extent to which local effects of the injury (damage to tissues and disuse atrophy of muscles) contribute to this outpouring of nitrogen appears to have received little attention. The only direct measurements of loss of tissue from fractured limbs are those of Cuthbertson, McGirr and Robertson¹, who studied rats. These investigators fractured one femur of each rat, and on the tenth day after injury the animals were killed and both hind limbs were weighed. The average difference in weight between the sound limb and the injured limb was 1·03 gm. Assuming the material lost from the injured limb to have been muscle, they calculated that this difference in weight was equivalent to a loss of 32·2 mgm. nitrogen. There was, however, an average excess output of 425 mgm. nitrogen in the urine during the first nine days after fracture. From these observations it would seem that very little of the excess nitrogen excreted after fracture comes from the tissues of the injured limb.