Frontal plane knee angle affects dynamic postural control strategy during unilateral stance.

PURPOSE Center of plantar pressure (COPP) location moves toward the forefoot as ankle plantar flexor muscles attempt to maintain postural control during single leg stance. This study evaluated relationships between frontal plane tibiofemoral joint angulation during relaxed bilateral stance and mean COPP locations during vision-denied single leg stance at 20 degrees knee flexion. METHODS Fifty-six nonimpaired athletes (29 female, 27 male) were evaluated for frontal plane tibiofemoral joint angulation and standing foot angle by using two-dimensional videography (30 Hz). Mean anterior-posterior and mediolateral COPP locations were assessed during single leg stance on a mat (25 Hz, 15 s). One-way ANOVA and Tukey HSD tests evaluated group differences (P < or = 0.05) based on frontal plane tibiofemoral joint angulation. RESULTS Group 1 (genu varus or genu valgus < 5 degrees ) displayed a mean anterior-posterior COPP location of 54.2 +/- 6% from the (0,0) coordinate starting point at the anterolateral foot (10.3 +/- 2 cm from the posterior sensor edge). Group 2 (genu varus angulation > or = 5 degrees ) and group 3 subjects (genu valgus angulation > or = 5 degrees ) displayed mean anterior-posterior COPP locations of 60.6 +/- 8% and 60.7 +/- 7% (8.8 +/- 2 cm and 8.7 +/- 2 cm from the posterior sensor edges), respectively. Group 2 (12.5 +/- 3 N x kg(-1)) and group 3 (12.4 +/- 3.1 N x kg(-1)) subjects also displayed greater mean plantar force magnitude/body weight than group 1 (10.3 +/- 2 N x kg(-1)) subjects. Mean ankle plantar flexor moment magnitudes did not differ between groups. CONCLUSIONS Rearfoot directed mean anterior-posterior COPP locations and greater plantar force magnitudes/body weight suggests that subjects with genu varus or genu valgus relied more on the subtalar and midtarsal joint control function of the ankle plantar flexor muscle group for lower extremity dynamic postural control.