The present disclosure provides an inventive method of treating inflammation that is associated with osteoarthritis of the knee joint by injecting mesenchymal stem cells into the symptomatic knee. In one aspect, the mesenchymal stem cells are obtained autogenously. In another aspect, the mesenchymal stem cells are injected below the degenerated medial tibial plateau of the knee joint, resulting in reduction of the inflammation and alleviation of the symptoms of the osteoarthritis.