Kinematic analysis of functional lower body perturbations

Background Sudden changes in direction on a single weight-bearing-limb are commonly associated with injury to the lower extremity. The purposes of this study were to assess the between day reliability of hip, knee, and ankle kinematic displacements achieved with internal and external femur-on-weight-bearing-tibia rotation perturbations and to determine the effect of these perturbations on three dimensional hip, knee and ankle kinematics. Methods Twenty recreationally active, healthy college students with no history of significant orthopedic injury (10 male, 10 female) were subjected to a forward and either internal or external rotary perturbation of the trunk and thigh on the weight-bearing-tibia while three dimensional kinematics were simultaneously collected. The protocol was repeated 24–48 h later to assess reliability. Findings External perturbations resulted in significant internal rotation (IR) of the tibia on the femur (mean 7.3 (SD 3.9°)) and IR of the femur on the pelvis (mean 6.8 (SD 5.4°)) (P < 0.05). Internal perturbations resulted in significant external rotation (ER) of the tibia on the femur (mean 6.8 (5.9°)) and ER of the femur on the pelvis (mean 10.7 (SD 96.1°)) (P < 0.05). Additionally the external perturbation results in a significantly greater knee valgus (mean 3.6 (SD 2.2°)) position while the internal perturbation results in a significantly greater knee varus position (mean 2.3 (SD 3.5°)) (P < 0.05). External perturbation hip and knee total joint displacements revealed moderate to strong reliability (Intraclass Correlation Coefficient2,k = 0.67–0.94) while internal perturbations revealed slightly higher Intraclass Correlation Coefficients2,k(0.80–0.96). Interpretation The lower extremity perturbation device provides a consistent external and internal perturbation of the femur on the weight-bearing-tibia. The observed transverse and frontal plane kinematics are similar to motions observed during cross-over and side-stepping tasks.