• Jakob Ackermann, Gergo Merkely, Alexandre Barbieri Mestriner, Nehal Shah, and Andreas H Gomoll.
• Sports Medicine Center, Massachusetts General Hospital, Boston, Massachusetts, USA.
• Am J Sports Med. 2019 Oct 1; 47 (12): 2919-2926.

BackgroundAssays to quantitate the quality of autologous chondrocyte implants have recently become available. However, the correlation of the assay score with radiological and clinical outcomes has not been established.Purpose/HypothesisThe purpose was to assess the influence of cell identity (chondrocyte/synoviocyte gene expression ratio) and viability on patient-reported outcome measures, graft survival, and repair tissue quality. It was hypothesized that greater cell product quality as assessed through an identity assay and cell viability is associated with superior outcomes after autologous chondrocyte implantation (ACI) for symptomatic cartilage defects.Study DesignCohort study; Level of evidence, 3.MethodsSeventy-nine patients with a minimum follow-up of 2 years were included in this study. Of these, 67 patients were available for imaging assessment utilizing the Magnetic Resonance Observation of Cartilage Repair Tissue (MOCART) scoring system. Patients were assigned to groups either below or above the cohort's mean based on their individual cell identity score and viability percentage.ResultsPatients were predominantly female (57.7%) with a mean age of 30.0 ± 9.3 years. No differences were seen between Knee injury and Osteoarthritis Outcome Score, Lysholm, Tegner, or International Knee Documentation Committee Subjective Knee Evaluation Form within the viability and cell identity groups at a final follow-up of 3.8 ± 1.4 years after ACI (P > .05). In a subset of patients, the mean MOCART score was 68.3 ± 15.6 at an average magnetic resonance imaging follow-up of 17.7 ± 9.56 months. Low cell identity was significantly associated with the degree of defect filling (P = .025), integration of border zone (P = .01), effusion (P = .024), and ACI graft failure (P = .002). Patients with above-average cell identity scores had a significantly higher survival rate at 5-year follow-up compared with patients with below-average scores (95.8% vs 64.7%; P = .013). Cell viability did not influence MOCART subscales or graft failure (all P > .05). Cell viability and identity showed no significant correlation with each other (r = -0.045; P = .694).ConclusionCell identity was significantly correlated with structural repair quality and graft survival after second-generation ACI for symptomatic chondral lesions in the knee. While improved imaging outcome and higher graft survivorship were associated with a higher individual cell identity score indicating a higher chondrocyte/synoviocyte gene expression ratio in the final cell product, clinical outcome did not correlate with the identity score.

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