Comparison of various icing times in decreasing bone metabolism and blood flow in the knee.

In a previous study we used technetium-99m bone scans to show that cooling a knee for 20 minutes with a standard ice wrap will decrease soft tissue blood flow by a mean of 26%, and skeletal blood flow and metabolism by 19%. The present study examined the effects of shorter and longer icing periods to determine minimum cooling time for a measurable and consistent decrease, and time to produce maximal decrease within a safe period of icing (< 30 minutes). Thirty-eight subjects were studied. An ice wrap was applied to one knee for an assigned time (5, 10, 15, 20, or 25 minutes). Triple-phase bone scans of knees were obtained; mean percentages of decrease in the iced knee for each of the five time groups at each of the three phases of the bone scan were calculated and compared. Mean decreases of 11.1% in soft tissue blood flow, and 5.1% in skeletal metabolism and blood flow were measured at 5 minutes; maximums of 29.5% and 20.9%, respectively, were obtained at 25 minutes. A small but consistent decrease in soft tissue blood flow and skeletal blood flow and metabolism in a knee appear to be obtained with as little as 5 minutes of ice application. This effect is time-dependent and can be enhanced three- to four-fold by increasing the ice application time to 25 minutes.