Osteochondral unit–based management of focal articular cartilage and osteochondral defects: a narrative review of surgical repair, clinical decision-making, and tissue engineering

The therapeutic goal for articular cartilage and osteochondral defects has increasingly emphasized osteochondral unit reconstruction. This review uses the principal osteochondral tissues targeted by each strategy as a framework to compare marrow stimulation, scaffold enhancement, osteochondral transplantation (autograft or allograft), cell-mediated regeneration, and engineered regeneration strategies in terms of their indications, clinical outcomes, limitations, and translational boundaries. A structured narrative synthesis was performed after searching PubMed and screening clinical studies, systematic reviews, and representative translational and preclinical studies; 127 references were ultimately included. Current evidence indicates that procedure selection is primarily informed by defect size and depth, subchondral bone status, lesion location, prior surgical history, and joint mechanical environment. Microfracture may be used for small, contained defects with limited subchondral bone involvement, but the long-term durability of the repair tissue remains inadequate. Autologous Matrix-Induced Chondrogenesis (AMIC) can enhance the reparative environment after marrow stimulation, yet evidence heterogeneity remains substantial across lesions and techniques. Osteochondral Autograft Transplantation (OAT) is suitable for small-to-medium, well-defined osteochondral defects in patients with high functional demands, although it is limited by autologous donor-site availability. Osteochondral Allograft Transplantation (OCA) can provide single-stage structural reconstruction for medium-to-large lesions involving subchondral bone or after previous treatment failure, but still faces challenges in graft availability, osseous integration, graft failure, and reoperation burden. Autologous Chondrocyte Implantation/Matrix-induced autologous chondrocyte implantation (ACI/MACI) is more applicable to medium-to-large focal full-thickness chondral defects, provided that the subchondral bone is largely intact or can be reconstructed concomitantly; its long-term outcomes are constrained by patient selection, correction of joint mechanics, rehabilitation duration, and cost. Hydrogels, biphasic or multiphasic scaffolds, and 3D bioprinting enable stratified biomimetic reconstruction, yet clinical evidence lags behind basic research. Therefore, articular cartilage repair should be individualized according to the osteochondral tissues involved and the extent of involvement, with concomitant correction of malalignment, joint instability, and meniscal deficiency. Future research should use standardized outcomes, long-term follow-up, and high-quality comparative studies to clarify the true added value and clinical translatability of emerging strategies relative to established procedures.