Differences in healing of skin wounds caused by burn and freeze injuries

Circular, full-thickness dermal burn- and freeze-produced wounds were produced in rats to compare the difference in healing between the two types of thermal injuries. Contraction did not occur in wounds (n = 30) caused by freezing, while burn wounds (n = 30) contracted to less than one-third of original size by 21 days after injury. If the centers of the freeze-produced wounds (n = 12) were excised, contraction would then occur and proceed at the same rate as an open wound. Histologically, the degree of initial tissue destruction by the two types of injuries was similar. The burn wound contained only half the amount of collagen found in the freeze-produced wound. There was a greater and more rapid replacement of collagen in the burn wounds. With both injuries, the highest concentration of collagen was found on the fifteenth day and returned to normal by the twenty-eighth day. The burn wound contained three times the amount of collagen in normal skin, while the freeze-produced wound contained only 1 3/4 times the amount in normal skin. Contraction does not seem to occur in the healing of the freeze-injured skin because the slow removal and replacement of the residual matrix prevents contraction.