Articular cartilage defects in the knee have a poor intrinsic healing capacity and may lead to functional disability and osteoarthritis. Cartilage cell therapy using autologous chondrocyte implantation (ACI) has been established as the first advanced treatment therapy medicinal product. Although this technique has achieved good mid-term results, it is a costly and extensive two-stage procedure which is limited by the number of chondrocytes obtained by biopsy and the dedifferentiation resulting from the expansion phase. Therefore, there is a need for improvement. A new cartilage repair technique should aim at decreasing surgical trauma, lowering complexity, improving logistics and cost-effectiveness while retaining or improving clinical outcome. Direct contact between mesenchymal stromal cells (MSCs) and dedifferentiated articular chondrocytes in vitro showed improvement of the chondrogenic phenotype of dedifferentiated articular chondrocytes. In addition, preserving the pericellular matrix of chondrocytes improves cartilage formation. These chondrons (chondrocytes with their pericellular matrix) have shown improved cartilage formation when combined with allogeneic MSCs in extensive preclinical studies. The cells are mixed with fibrin cell carrier and applied to the cartilage lesion within one surgical procedure. This will reduce patient morbidity and improve patient care through immediate transplantation of a potent cell-based cartilage product. This is a phase I/II prospective monocenter study to evaluate the safety and feasibility of the IMPACT for treatment of focal articular cartilage lesions of the knee.

Inclusion Criteria:

• Age >18 and <45 years old
• Symptomatic isolated full-thickness articular cartilage lesion on the femoral condyle or trochlea.
• Size 2 - 8 cm2
• Intact anterior cruciate ligament

Exclusion Criteria:

• (History of) osteoarthritis, defined as Kellgren-Lawrence grade >3 as determined from appropriate X-ray.
• Concomitant inflammatory disease that affects the joint (rheumatoid arthritis, metabolic bone disease, psoriasis, gout, symptomatic chondrocalcinosis)
• (History of) Septic arthritis.
• Malalignment requiring an osteotomy.
• (History of) total menisectomy in the target knee joint.
• Any surgery in the knee joint 6 months prior to study inclusion.
• Risk groups for MRI scanning due to the magnetic field like patients with pacemakers, nerve stimulators, metal particles, stents, clips or implants, (possible) pregnancy or breast feeding.
• Patients with severe anxiety for MRI scans and/or needles

All patients were monitored for the duration of 18 months after surgery, at fixed time points (at 7 days, 6 weeks and 3,6,12 and 18 months after surgery), for inflammation and signs of a foreign body response by an independent physician (rheumatologist) using standardized clinical measures, pain assessment by numeric rating scale for pain and blood analysis including serum C-reactive protein (CRP), erythrocyte sedimentation rate (ESR) and leukocyte count.