The Incidence and Clinical Relevance of Graft Hypertrophy After Matrix-Based Autologous Chondrocyte Implantation

Background: Graft hypertrophy is the most common complication of periosteal autologous chondrocyte implantation (p-ACI). Purpose: The aim of this prospective study was to analyze the development, the incidence rate, and the persistence of graft hypertrophy after matrix-based autologous chondrocyte implantation (mb-ACI) in the knee joint within a 2-year postoperative course. Study Design: Case series; Level of evidence, 4. Methods: Between 2004 and 2007, a total of 41 patients with 44 isolated cartilage defects of the knee were treated with the mb-ACI technique. The mean age of the patients was 35.8 years (standard deviation [SD], 11.3 years), and the mean body mass index was 25.9 (SD, 4.2; range, 19-35.3). The cartilage defects were arthroscopically classified as Outerbridge grades III and IV. The mean area of the cartilage defect measured 6.14 cm2 (SD, 2.3 cm2). Postoperative clinical and magnetic resonance imaging (MRI) examinations were conducted at 3, 6, 12, and 24 months to analyze the incidence and course of the graft. Results: Graft hypertrophy developed in 25% of the patients treated with mb-ACI within a postoperative course of 1 year; 16% of the patients developed hypertrophy grade 2, and 9% developed hypertrophy grade 1. Graft hypertrophy occurred primarily in the first 12 months and regressed in most cases within 2 years. The International Knee Documentation Committee (IKDC) and visual analog scale (VAS) scores improved during the postoperative follow-up time of 2 years. There was no difference between the clinical results regarding the IKDC and VAS pain scores and the presence of graft hypertrophy. Conclusion: The mb-ACI technique does not lead to graft hypertrophy requiring treatment as opposed to classic p-ACI. The frequency of occurrence of graft hypertrophy after p-ACI and mb-ACI is comparable. Graft hypertrophy can be considered as a temporary excessive growth of regenerative cartilage tissue rather than a true graft hypertrophy. It is therefore usually not a persistent or systematic complication in the treatment of circumscribed cartilage defects with mb-ACI

Graft Maturation of Autologous Chondrocyte Implantation

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 cm2. 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