Biomechanical and neuromuscular adaptations during the landing phase of a stepping-down task in patients with early or established knee osteoarthritis

Background: To compare the knee joint kinematics, kinetics and EMG activity patterns during a stepping-down task in patients with knee osteoarthritis (OA) with control subjects. Methods: 33 women with knee OA (early OA, n = 14; established OA n = 19) and 14 female control subjects performed a stepping-down task from a 20. cm step. Knee joint kinematics, kinetics and EMG activity were recorded on the stepping-down leg during the loading phase. Results: During the stepping-down task patients with established knee OA showed greater normalized medial hamstrings activity (p = 0.034) and greater vastus lateralis-medial hamstrings co-contraction (p = 0.012) than controls. Greater vastus medialis-medial hamstrings co-contraction was found in patients with established OA compared to control subjects (p = 0.040) and to patients with early OA (p = 0.023). Self-reported knee instability was reported in 7% and 32% of the patients with early and established OA, respectively. Conclusions: The greater EMG co-activity found in established OA might suggest a less efficient use of knee muscles or an attempt to compensate for greater knee laxity usually present in patients with established OA. In the early stage of the disease, the biomechanical and neuromuscular control of stepping-down is not altered compared to healthy controls.