BACKGROUND:Chondral lesions in athletically active patients cause considerable morbidity, and treatment with existing cell-based therapies can be challenging. Bone marrow has been shown as a possible source of multipotent stem cells (MSCs) with chondrogenic potential and is easy to harvest during the same surgical procedure. PURPOSE:To investigate the clinical outcome in a group of active patients with large full-thickness chondral defects of the knee treated with 1-step surgery using bone marrow-derived MSCs and a second-generation matrix. STUDY DESIGN:Case series; Level of evidence, 4. METHODS:From January 2007 to February 2010, 25 patients (average age, 46.5 years) with symptomatic large chondral defects of the knee (International Cartilage Repair Society grade 4) who underwent cartilage transplantation with MSCs and a collagen type I/III matrix were followed up for a minimum of 3 years. The average lesion size was 8.3 cm(2). Coexisting injuries were treated during the same surgical procedure in 18 patients. All patients underwent a standard postoperative rehabilitation program. Preoperative and postoperative evaluations at 1-year, 2-year, and final follow-up included radiographs, magnetic resonance imaging (MRI), and visual analog scale (VAS) for pain, International Knee Documentation Committee (IKDC), Knee injury and Osteoarthritis Outcome Score (KOOS), Lysholm, Marx, and Tegner scores. Seven patients underwent second-look arthroscopic surgery, with 4 consenting to a tissue biopsy. RESULTS:No patients were lost at final follow-up. The average preoperative values for the evaluated scores were significantly improved at final follow-up (P < .001): VAS, 5.4 ± 0.37 to 0.48 ± 0.19; IKDC subjective, 37.92 ± 4.52 to 81.73 ± 2.42; KOOS pain, 61.04 ± 3.95 to 93.32 ± 1.92; KOOS symptoms, 55.64 ± 3.23 to 89.32 ± 2.32; KOOS activities of daily living, 63.96 ± 4.48 to 91.20 ± 2.74; KOOS sports, 34.20 ± 5.04 to 80.00 ± 3.92; KOOS quality of life, 32.20 ± 4.43 to 83.04 ± 3.37; Lysholm, 46.36 ± 2.25 to 86.52 ± 2.73; Marx, 3.00 ± 0.79 to 9.04 ± 0.79; and Tegner, 2.12 ± 0.32 to 5.64 ± 0.26. Patients younger than 45 years of age and those with smaller or single lesions showed better outcomes. The MRI scans showed good stability of the implant and complete filling of the defect in 80% of patients, and hyaline-like cartilage was found in the histological analysis of the biopsied tissue. No adverse reactions or postoperative complications were noted. CONCLUSION:The treatment of large chondral defects with MSCs is an effective procedure and can be performed routinely in clinical practice. Moreover, it can be achieved with 1-step surgery, avoiding a previous surgical procedure to harvest cartilage and subsequent chondrocyte cultivation.