Cell Co-Implantations With Chondrocytes for Cartilage Repair: A Systematic Review of <i>In Vivo</i> Results

ObjectivesDamaged articular cartilage cannot regenerate spontaneously. Chondrocyte therapy, the current treatment of choice, requires laboratory expansion, necessitating two surgical procedures. Adding a second cell type to intraoperatively isolated chondrocytes enables single-stage chondrocyte-based repair strategies and has shown promise <i>in vitro</i>. The benefit of this strategy <i>in vivo</i> and in the clinic has not yet been comprehensively assessed. This systematic review assesses the efficacy of cartilage repair by co-implantations of chondrocytes with other cell types over all available <i>in vivo</i> studies.DesignMedline, Embase and Cochrane databases were searched for studies on co-implantations of chondrocytes with other cell types for hyaline cartilage repair. For each study, extracted data were tabulated and reporting quality and risk of bias were assessed. Studies were categorized based on their control groups for qualitative synthesis.ResultsThe search yielded 48 studies across 46 publications: 44 animal studies (26 ectopic and 18 orthotopic) and four clinical trials. Ectopic studies scored poorly on reporting quality and bias, while orthotopic studies were only moderately better. Twenty-seven of 27 experiments with chondrocyte-only controls demonstrated synergistic cartilage formation through co-implantation. Cartilage formation by co-implantations was also found in 15 of 17 experiments without such control and in four clinical trials.ConclusionCartilage repair by articular chondrocytes is improved by adding a second cell type, like mesenchymal stromal cells. This is likely caused by the second cell types' stimulatory support. Other second cell types and chondrocyte sources have shown promising results too. This is encouraging for further clinical exploration of single-stage co-implantation strategies.