Static imaging has been commonly and clinically accepted to assess the severity of medial knee osteoarthritis (KOA), especially the radiography. Gait analysis has been adopted to evaluate the kinematic characteristics of the knees in patients with KOA. Most of the current studies focus on the sagittal plane of the knee, but very few of them focus on the frontal or horizontal plane. With the different severity of medial KOA, anatomical structures of the knees will change and influence kinematics of the knees, such as osteophytes and deformity. At present, there has been no study focusing on the relations between the imaging assessment of the severity and quantitative kinematics of medial KOA. The aim of the study is to explore the relationship between the imaging assessment based on the Kellgren-Lawrence Scores and in vivo 3D knee kinematic characteristics in Chinese patients with medial KOA during walking using a new portal gait system.

All patients are assessed according to the Kellgren-Lawrence Score.

Inclusion Criteria:

1. Clinical diagnosis of medial knee osteoarthritis according to the American College of Rheumatology criteria.
2. The patients are confirmed by radiographic evidence that medial tibiofemoral joint space grade was narrower than lateral tibiofemoral joint space.
3. The patients have clinical symptom of medial pain of the knee.
4. Clinical examinations are taken to examine the asymptomatic subjects to avoid knee diseases.

Exclusion Criteria:

1. Traumatic knee osteoarthritis.
2. Lateral tibiofemoral KOA or any other types of Knee OA.
3. Ambiguity of Kellgren-Lawrence scores
4. History of surgery.
5. Neuromuscular disease, cardiovascular disease or trauma that can affects gait.
6. Body mass index greater than 35.
7. Needing stick or assistance to walk or unable to walk at a speed of less than 2.0 km/h and less than 300 m.

Chinese patients diagnosed with medial KOA andasymptomatic participants will be recruited. The asymptomatic participants（>35 years） have no history of knee pain, trauma, surgery, or obvious gait abnormalities.