Sixty patients with knee cartilage lesions were randomized to receive knee arthroscopic therapy with an injection of mesenchymal stromal cell concentrates source from the infrapatellar fat pad (n=30) or saline (n=30) into the joint cavity. The outcomes of interest included pain at rest and during motion on a Visual Analogue Scale (VAS), the Western Ontario and McMaster Universities Osteoarthritis (WOMAC) index total score and associated sub-scores (pain; stiffness; function), and the Magnetic Resonance Observation of Cartilage Repair Tissue (MOCART) score to assess cartilage regeneration. All outcomes were assessed at 6 weeks, 12 weeks, 6 months, and 12 months post-operation. Results of the study revealed no statistical significant differences between the two groups in VAS pain scores at rest and during motion, and WOMAC pain, stiffness, function and total scores at 6 weeks and 12 weeks post-operation (p>0.05 for all). Moreover, WOMAC function and total scores were statistically significantly in favour of the injection group compared to the control group at 6 and 12 months post-operation (p<0.05 for all), whilst WOMAC pain scores, VAS pain scores at rest and during motion, and MOCART scores were statistically significantly in favour of the injection group at 12 months post-operation only (p<0.05 for all).