The effects of exercise, ice, and ultrasonography on torsional laxity of the knee.

Changes in torsional knee laxity, after subjects ran 3.5 miles during a 30-minute period, were studied in 13 subjects. The effects of ice and ultrasonographic treatments on these laxity changes were then investigated. Knee laxity was determined by measuring torque versus rotation responses of the tibia at 90 degrees of knee flexion. Total rotational laxity of the tibia was tabulated at +/- 10 newton-meters of applied torque. There were significant increases in postexercise laxities over preexercise levels for internal and external tibial rotation. Postexercise laxity changes followed a uniform time course of recovery. The maximum postexercise laxity represented a mean increase of 14% over pre-exercise levels, with a mean recovery time of 52.4 minutes and a standard deviation of 17.8 minutes. The application of ten-minute treatments of either ice or ultrasonography significantly reduced postexercise recovery times, to 20.0 +/- 4.6 SD and 20.9 +/- 6.4 SD, respectively. A common clinical assumption, that cold and heat have opposite effects on knee laxity, was found invalid. In the authors' study, ice and ultrasonography had equivalent effects in accelerating the return to pre-exercise laxities. No laxity changes were observed in unexercised subjects, with either ice or ultrasonographic treatments. The time course of laxity recovery and the subsequent effects of heat and ice are important clinically. Immediately after injury, both knees are more lax than normal, and after approximately one hour, recovery to pre-exercise laxity levels will be complete for the uninjured leg. Ice (or ultrasonography) will shorten this time to 20 minutes. If these recovery time courses are recognized and taken into account, a more accurate diagnosis can be made during this "golden opportunity" period before pain and swelling ensue. The fact that ice and ultrasonography have identical effects on the time course of recovery in the exercised knee raises new questions and suggests additional areas for future work in the recently developing field of sports medicine biomechanics.