Muscle strength in knee varus and valgus

Purpose: The purpose of this study was to investigate the lower-limb muscle strength in knee varus-valgus and its dependence on knee varus-valgus posi tion. The hypothesis was that humans could differentially contract the medi al and lateral muscles crossing the knee and generate significant moments i n knee valgus-varus. Methods: The subjects sat with the knee at full extens ion and secured from the medial, lateral, anterior, and posterior sides. Bo th hips were clamped from the lateral sides. The subjects adducted (abducte d) the ipsilateral hip during the knee valgus (varus) maximal voluntary con traction with EMG signals recorded from muscles crossing the knee and knee joint moments measured using a six-axis force sensor. Frontal plane tibiofe moral movement was evaluated using a fluoroscope. Results and Conclusions: The subjects differentially contracted the medial and lateral muscles, and fluoroscope images showed the corresponding tibiofemoral movement. The subj ects showed considerable strength in knee varus and valgus. The active knee varus strength increased significantly with increasing knee valgus angle, and the valgus strength was significantly higher when the knee was in varus position (P < 0.039). Active valgus muscle strength at 5 degrees knee varu s was significantly higher than the active varus strength at 5 degrees valg us (P = 0.002). The passive resistance moment increased linearly with incre asing knee valgus and varus angles, and it accounted for 28% and 35% of the total (active plus passive) moment at the 50 varus and 5 degrees valgus, r espectively. The significant varus-valgus muscle strength demonstrated in t his study may play important roles in performing various functional tasks, maintaining joint stability, and preventing potential injuries, whether the major load and motion at the knee is in the frontal plane or not.