Tibial torque generation in a flexed weight-bearing stance.

Internal and external torque generated about the long axis of the lower extremity was measured in 18 male subjects who were instructed to twist with maximal effort against a fixed footplate containing an instrumented torque cell. Mean torque values ranged from 30 to 71 newton meters (Nm) depending upon the test conditions. Torques recorded during the flexed single-leg stance were 19% to 49% higher than those measured while seated. Values at 45 degrees of knee flexion were 11% to 16% greater than those at 20 degrees. Torques generated while wearing a ski boot were 8% to 11% greater than those recorded in an athletic shoe. When movement of the pelvis and upper torso was allowed, torque values were 17% to 49% higher than those recorded when the hips and shoulders were restrained which allowed only lower leg musculature to act in an isolated fashion. There were no differences between internal versus external generated torques when the hips and torso were restrained. When the hips and shoulders were unrestrained, internal torque was 12% greater than external torque. There were no strong correlations between generated torque and body weight or height. These generated torque values suggest that if ski bindings are set to American Society for Testing and Materials (ASTM) standards for twist-release torque, then upper torso and pelvic movement in conjunction with tensed knee musculature (i.e., a "locked knee") may be necessary to accomplish binding release. Use of the lower leg musculature alone (i.e., ankle twist) may not generate sufficient torque for release.

Flow characteristics of acrylic bone cements.

Flow properties of Simplex, Zimmer Regular, Zimmer LVC, and Sulfix bone cements were measured as functions of time between two and five minutes after mixing. The mass flowrates measured for Zimmer Regular and Simplex were quite similar in the temperature range of 20.0 degrees -23.3 degrees. At 18.3 degrees Simplex had approximately double the flowrate of Zimmer Regular two minutes after mixing. The flowrate for LVC was approximately four times that measured for Zimmer Regular at 20.0 degrees. Sulfix displayed the greatest sensitivity of flowrate with temperature; at 18.3 degrees its flow characteristics were similar to those of LVC, and at 23.3 degrees it behaved more like Simplex and Zimmer Regular. All cements demonstrated substantial relative increases in flowrates with only slight increases in pressure; Sulfix was the most pressure sensitive. Set times for Zimmer, LVC, and Sulfix were virtually identical, ranging from a mean of 11 minutes (at 18.3 degrees) to 7.5 minutes (at 23.3 degrees). Simplex had considerably longer set times, averaging 15.8 minutes (at 18.3 degrees) and 9.4 minutes (at 23.3 degrees). Although Simplex demonstrated the greatest sensitivity of set time with temperature (almost double that measured for the other 3 cements), it did not show the greatest sensitivity of flowrate with temperature.

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.