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Study Design: Case study.

Objective: To compare knee kinematics and moments of nongiving way trials to a giving way trial during a combined stepping and crossover cutting activity.

Background: The knee kinematics and moments associated with giving way episodes sugge motor control strategies that lead to instability and recovery of stability during movement.

Methods and Measures: A 27-year-old woman with anterior cruciate ligament deficiency reported giving way while performing a combined stepping and crossover cutting activity. P motion analysis system recorded motion of the pelvis, femur, tibia, and foot using 3 infrarec emitting diodes placed on each segment at 60 Hz. Force plate recordings at 300 Hz were combined with limb inertial properties and position data to estimate net knee joint moments. The stance time, foot progression angle, and cutting angle were also included to evaluate performance between trials.

Results: Knee internal rotation during the giving way trial increased 3.2' at 54% of stance relative to the nongiving way trials. Knee flexion during the giving way trial increased to 33.1" at 66% of stance, and the knee moment switched from a nominal flexor moment to 2 knee extensor moment at 64% of stance. The knee abductor moment and external rotation moment during the giving way trial deviated in early stance.

Conclusions: The observed response to the giving way event suggests that increasing knee flexion may enhance knee stability for this subject. The transverse and frontal plane moments appear important in contributing to the giving way event. Further research that assists clinicians in understanding how interventions can impact control of movements in these planes is necessary.