This study will evaluate the safety, feasibility and efficacy of a novel medical device (a synovial brush) and procedure (synovial brushing) to increase the number of autologous minimally manipulated MSCs in the knee. Twenty patients undergoing microfracture for isolated chondral defects will be randomly assigned to either a control group (microfracture only, 10 patients) or the intervention group (microfracture plus synovial brushing, 10 patients). The device is intended to increase the number of MSCs within the joint as a final stage during surgery, aiding repair by bolstering those MSCs recruited from the bone marrow.