Relationship between knee alignment in asymptomatic subjects and flexibility of the main muscles that are functionally related to the knee

OBJECTIVE: To assess the relationship between static frontal knee alignment in asymptomatic subjects and flexibility of the main muscles functionally related to the knee. METHODS: A descriptive cross-sectional study was performed in 33 healthy adults (19–31 years). The frontal knee angle (valgus/varus angle) was measured by photogrammetry and it was measured in the lateral side. Therefore, high values were assigned for genu varum and low values for genu valgum. Iliopsoas, gluteus maximus and medius, rectus femoris, biceps femoris, vastus of the quadriceps, and gastrocnemius muscles were stretched. Muscles were classified as normal, reflex hypomobile, or structural hypomobile. RESULTS: Women had significantly greater valgus than did men (right angle, women: 174.41°/men: 177.41°; left angle, women: 174.20°/men: 178.70°). The right frontal plane knee angle was higher in women with structural hypomobile vastus. The left frontal plane knee angle was higher in women with structural hypomobile iliopsoas. No relationships were found in men. CONCLUSIONS: A tighter vastus of the quadriceps and tighter iliopsoas are related to greater genu varum in adult women. Stretching the vastus of the quadriceps and iliopsoas when there is a tendency for excess varus in the knee, to prevent overuse injury or early osteoarthritis, might be clinically relevant.