BACKGROUND

Autologous chondrocyte implantation (ACI) using tissue-engineered cartilage is a successful therapy for full-thickness cartilage lesions in the knee joint. However, in vivo graft maturation is still unclear.

PURPOSE

The aim of this prospective study was to analyze graft maturation after ACI in the knee using objective T2 mapping in correlation with the clinical outcomes within a 3-year postoperative course.

STUDY DESIGN

Case series; Level of evidence, 4.

METHODS

A total of 13 patients with isolated cartilage defects of the knee were treated with Novocart 3D, a matrix-based ACI procedure in the knee joint. The patients had complete data from International Knee Documentation Committee (IKDC) scores and MRI examinations for 6 to 36 months postoperatively. All cartilage defects were arthroscopically classified as Outerbridge grades III and IV. The mean area of the cartilage defect was 5.6 cm(2). Postoperative clinical and MRI examinations were conducted at 6, 12, 24, and 36 months after surgery. The modified magnetic resonance observation of cartilage repair tissue (MOCART) score was used to evaluate the quality and integration of the Novocart 3D implants on MRI. The T2 relaxation time values of the ACI graft and healthy native cartilage areas were determined to assess graft maturation using T2 mapping.

RESULTS

The T2 relaxation times of the ACI graft showed significant improvement, with decreasing values from 41.6 milliseconds at 6-month follow-up to 32.4 and 30.9 milliseconds after 24 and 36 months, respectively. These values were similar to the T2 relaxation times of the native surrounding cartilage. There was no correlation between the clinical outcomes (IKDC score) and T2 relaxation time values.

CONCLUSION

The T2 relaxation time in the repaired tissue showed similar values compared with normal hyaline cartilage. Graft maturation after ACI in the knee joint needs at least 1 year, with ongoing adjustment of the T2 relaxation time values compared with native surrounding cartilage. A correlation between increasing ACI graft maturation and clinical outcomes (IKDC score) could not be found with the data available.