Tibiofemoral joint positioning for the valgus stress test.

CONTEXT Recommendations on the positioning of the tibiofemoral joint during a valgus stress test to optimize isolation of the medial collateral ligament (MCL) from other medial joint structures vary in the literature. If a specific amount of flexion could be identified as optimally isolating the MCL, teaching and using the technique would be more consistent in clinical application. OBJECTIVE To determine the angle of tibiofemoral joint flexion between 0 degrees and 20 degrees that causes a difference in the slope of the force-strain line when measuring the resistance to a valgus force applied to the joint. DESIGN Cross-sectional study. SETTING University research laboratory. PATIENTS OR OTHER PARTICIPANTS Twelve healthy volunteers (6 men, 6 women: age = 26.4 +/- 5.6 years, height = 170.9 +/- 8.4 cm, mass = 75.01 +/- 14.6 kg). INTERVENTION(S) Using an arthrometer, we applied a valgus force, over a range of 60 N, to the tibiofemoral joint in 0 degrees , 5 degrees , 10 degrees , 15 degrees , and 20 degrees of flexion. MAIN OUTCOME MEASURE(S) Force-strain measurements were obtained for 5 positions of tibiofemoral joint flexion. RESULTS As knee flexion angle increased, slope values decreased (F(4,44) = 17.6, P < .001). The slope at full extension was not different from that at 5 degrees of flexion, but it was different from the slopes at angles greater than 10 degrees of flexion. Similarly, the slope at 5 degrees of flexion was not different from that at 10 degrees of flexion, but it was different from the slopes at 15 degrees and 20 degrees of flexion. Further, the slope at 10 degrees of flexion was not different from that at 15 degrees or 20 degrees of flexion. Finally, the slope at 15 degrees of flexion was not different from that at 20 degrees of flexion. CONCLUSIONS When performing the manual valgus stress test, the clinician should fully extend the tibiofemoral joint or flex it to 5 degrees to assess all resisting medial tibiofemoral joint structures and again at 15 degrees to 20 degrees of joint flexion to further assess the MCL.