*2.2. Study Population*

This study enrolled 15 patients with cartilage defects at the weight-bearing site of the medial femoral condyle. The size of cartilage defects ranged from 0.6 to 4 cm<sup>2</sup> . Patients were enrolled in this study between September 2018 and June 2020. Patients were selected according to inclusion and exclusion criteria in Table S1. They were randomly allocated into groups of Kartigen® implantation (*n* = 10) or microfracture treatment (*n* = 5). Based on our previous study [34], the seeding density of CPs was 1.6–3.3 <sup>×</sup> <sup>10</sup><sup>6</sup> cells/cm<sup>2</sup> , and the total cell number was less than 1.32 <sup>×</sup> <sup>10</sup><sup>7</sup> cells. The schedule of study procedures and assessments is shown in Table S2.
