Problem: Cartilage lesions are commonly found during routine knee arthroscopy (60 to 63%). Among these injuries 11% to 23% are located in the patella and 6% to 15% in the trochlea. A low percentage of good to very good results (7%) treating patellar an trochlear lesions with ACI have been reported compared with 90% of success on femoral condyles. Few reports have evaluated quantitative assessment of cartilage repair in the PFJ with Chondrocyte Implantation comparing to Microfracture. Methods: Seventeen patients with full-thickness articular cartilage lesion in the Patello-femoral joint (PFJ) were randomized into two groups: Matrix Encapsulated Chondrocyte Implantation (MECI) or Microfracture (MF). Both procedures were performed by arthroscopy combining cartilage restoration procedures with unloading/realigning PFJ techniques. An identical rehabilitation protocol was implemented for both groups. Clinical assessment and T2-mapping-MRI were evaluated at 3, 12, 24 and 48 months. Results: Clinically the difference between baseline and 48 months post-op for both MECI and MF improve significant in Lysholm, IKDCs, KOOS (pain, DLA, Sport/Rec, symptoms & QoL) and Kujala (p<0.05). Tegner was significant between baseline and 48 months only for MECI (p<0.05). No significant difference was observed between groups for any of the evaluated scores at 3, 12, 24 & 4-years follow-up (p>0.05) (Tab. 1). T2-mapping values improved significantly over time in MECI compared to MF at 24 & 48-months (p<0.05). When comparing control values to MECI repaired tissue at 12, 24 and 48-month no significant different was (p<0.05) (Tab. 2). Conclusion: Clinically both techniques showed significant difference over the time. However, quantitative assessment showed that new-formed tissue with MECI improves significantly since 12-months post-operatively and maintain stable values compared to native cartilage until 48 months follow-up.