The investigators randomized patients undergoing HTO in combination with microfracture to receive either microfracture alone (control group, n = 5) or microfracture with collagen augmentation (experimental group, n=6). At postoperative one year, the clinical outcome in terms of Visual Analogue Scale of pain level (VAS), Knee Injury and Osteoarthritis Outcome Score (KOOS), International Knee Documentation Committee (IKDC) score, and Tegner scores were evaluated. In addition, second look arthroscopic examination and biopsy of regenerated cartilage were carried out when the HTO plate was removed at postoperative one year. Biopsy specimens were graded by International Cartilage Repair Society Visual Assessment Scale (ICRS II scores). Finally, radiologic outcome in terms of Magnetic Resonance Observation of Cartilage Repair Tissue (MOCART) scores was assessed using follow up MRI undertaken at postoperative one year.