To determine in vivo biomechanical properties of articular cartilage and cartilage repair tissue of the patella, using biochemical MRI by means of quantitative T2 mapping.

SY19-1107 MRI of cartilage Identification of early changes G.H. Welsch, S. Domayer, S. Apprich, M. Blanke, S. Marlovits, S. Trattnig Universitätsklinikum Erlangen, Trauma Surgery, Erlangen, Germany, Medical University of Vienna, Orthopedic Surgery, Vienna, Austria, Medical University of Vienna, Radiology, Vienna, Austria, Medizinische Universität Wien, Abt. Traumatologie, Wien, Austria Objectives: Besides the morphological description of cartilage repair tissue by means of MRI, different biochemical MRI techniques are seen to reflect different components of articular cartilage ultrastructure. Aim of this study was to exploit delayed gadolinium-enhanced MRI of cartilage (dGEMRIC), T2 mapping and diffusion weighted imaging (DWI) in a clinical approach in patients after cartilage repair: 1. to compare the ultrastructure of the repair tissue and native cartilage; 2. to correlate the biochemical parameters; 3. to assess their relation to the clinical outcome. Methods: Twenty patients (age: 34.7 ± 9 years, follow-up: 35.1 ± 20 months) after matrix-associated autologous chondrocyte transplantation (MACT) of the knee were included at 3T MRI. Besides morphological MRI, dGEMRIC, T2 mapping and DWI sequences were accomplished. A semi-automated zonal region of interest analysis was performed in the cartilage repair tissue and the surrounding native cartilage. Clinical testing was performed by the Lysholm score and the international knee documentation committee (IKDC) score. Statistical analysis-of-variance and Pearson correlation was performed. Results: 1. The repair tissue showed significant (p \ 0.001) lower dGEMRIC values compared to the reference cartilage. Comparably, DWI values showed significant (p \ 0.001) higher values for the repair tissue compared to the control cartilage, whereas T2 mapping showed less differences (p = 0.003 to p = 0.092). 2. The correlation of dGEMRIC and DWI was clearly significant (Pearson: 0.265–0.483). Nearly no correlation could be assessed in between dGEMRIC and T2 mapping, whereas T2 mapping and DWI showed in parts significant correlations (Pearson: 0.208– 0.415). 3. The correlation in between the clinical scores and the biochemical scores showed in many of the cases significant correlations, with moderate Pearson correlation coefficients in between 0.216 and 0.523. The clearest correlation could be assessed in between DWI and the clinical outcome, whereas T2 mapping as well as dGEMRIC and the clinical scoring revealed lower, and in parts not significant correlation coefficients. Conclusions: The results of the present study showed comparable results to existing in vitro and in vivo studies, however there is no study available reporting and comparing all three methodologies together in a clinical approach. Reflecting the composition of the repair tissue, dGEMRIC is seen to be sensitive for the glycosaminoglycan (GAG) content, T2 mapping for the collagen matrix and the hydration, and DWI for the diffusivity (intraand extracellular borders) within the tissue. In relation to the clinical results, the diffusivity might provide the most sensitive parameter for the present quality of the repair tissue, whereas GAG content and the collagen matrix might predict its future quality. Based on the present approach, in future clinical studies and trials, the composition/ultrastructure of the repair tissue can be quantified and assessed non-invasively.

The aim of this study was to investigate the effect of transplanted chondrocytes on endochondral bone formation in cartilage repair tissue. In the knee joint of miniature pigs, cartilage lesions were treated by microfracturing and were then either left empty, covered with a collagen membrane, or treated by matrix-associated autologous chondrocyte transplantation. In control lesions, the subchondral bone plate was left intact (partial-thickness lesion). The repair tissues were analyzed after 12 weeks by histological methods focusing on bone formation and vascularization. The effect of chondrocytes on angiogenesis was assessed by in vitro assays. The presence of antiangiogenic proteins in cartilage repair tissue, including thrombospondin-1 (TSP-1) and chondromodulin-I (ChM-I), was detected immunohistochemically and their expression in chondrocytes and bone marrow stromal cells was measured by quantitative RT-PCR. Significant outgrowths of subchondral bone and excessive endochondral ossification within the repair tissue were regularly observed in lesions with an exposed or microfractured subchondral bone plate. In contrast, such excessive bone formation was significantly inhibited by the additional transplantation of chondrocytes. Cartilaginous repair tissue that resisted ossification was strongly positive for the antiangiogenic proteins, TSP-1 and ChM-I, which were, however, not detectable in vascularized osseous outgrowths. Chondrocytes were identified to be the major source of TSP-1- and ChM-I expression and were shown to counteract the angiogenic activity of endothelial cells. These data suggest that the resistance of cartilaginous repair tissue against endochondral ossification following the transplantation of chondrocytes is associated with the presence of antiangiogenic proteins whose individual relevance has yet to be further explored.

The surface replacement of the hip as an alternative method to the implantation of a conventional hip prosthesis seems to be advantageous in consideration to bone conservation particularly for young patients.