Multicenter, open-label, controlled, non-randomized, double arm trial with a prospective treatment arm (GelrinC). This study compares the efficacy and safety of GelrinC to a historical control arm (microfracture) in the treatment of cartilage defects in the knee.

Main Inclusion Criteria:

• Age between 18 and 50.
• Single contained symptomatic lesion located on the femoral condyle of the femur graded as ICRS III or IV with less than 5 mm of bone loss below the subchondral plate.
• Lesion size between 1 and 5 cm2 post debridement, less than or equal to 2.5 cm in diameter.
• BMI ≤35
• Contralateral knee is asymptomatic, stable, fully functional and not medically treated.

Main Exclusion Criteria:

• Presence of an additional grade III or IV symptomatic lesion.
• Recent Osteochondritis Dissecans within 1 year of baseline visit.
• Untreated ACL and/or PCL deficiency or Complex ligamentous instability of the knee.
• Patient is excluded if presenting untreated current meniscal tear or if previous menisci resection was within the last 6 months.
• Previous tendon repair or ligament reconstruction within the last 6 months.
• Failed Mosaicplasty or ACI or MACI or any other cartilage repair product.
• Microfracture performed less than 1 year before baseline visit.