Quantitative 3-T Magnetic Resonance Imaging After Matrix-Associated Autologous Chondrocyte Implantation With Autologous Bone Grafting of the Knee: The Importance of Subchondral Bone Parameters

Background: Matrix-associated autologous chondrocyte implantation (MACI) with autologous bone grafting (ABG) is an effective surgical treatment for osteochondral defects. Quantitative magnetic resonance imaging (MRI) techniques are increasingly applied as noninvasive biomarkers to assess the biochemical composition of cartilage repair tissue. Purpose: To evaluate the association of quantitative MRI parameters of cartilage repair tissue and subchondral bone marrow with magnetic resonance morphologic and clinical outcomes after MACI with ABG of the knee. Study Design: Case series; Level of evidence, 4. Methods: Qualitative and quantitative 3 T MRI of the knee was performed in 21 patients (16 male) at 2.5 years after MACI with ABG at the medial (18/21) or lateral (3/21) femoral condyle for the treatment of osteochondral defects. Morphologic MRI sequences were assessed using MOCART (magnetic resonance observation of cartilage repair tissue) 2.0 scores. T2 relaxation time measurements for the assessment of cartilage repair tissue (CRT2) were obtained. Single-voxel magnetic resonance spectroscopy was performed in underlying subchondral bone marrow (BM) and at both central femoral condyles. The presence of pain and Tegner scores were noted. Statistical analyses included Student t tests, correlation analyses, and multivariate regression models. Results: The mean defect size was 4.9 ± 1.9 cm². At a follow-up of 2.5 ± 0.3 years, 9 of 21 patients were asymptomatic. Perfect defect filling was achieved in 66.7% (14/21) of patients. MOCART 2.0 scores (74.1 ± 18.4) did not indicate pain (68.3 ± 19.0 [pain] vs 81.7 ± 15.4 [no pain]; P =.102). However, knee pain was present in 85.7% (6/7) of patients with deep bony defects (odds ratio, 8.0; P =.078). Relative CRT2 was higher in hypertrophic cartilage repair tissue than in repair tissue with normal filling (1.54 ± 0.42 vs 1.13 ± 0.21, respectively; P =.022). The underlying BM edema–like lesion (BMEL) volume was larger in patients with underfilling compared with patients with perfect defect filling (1.87 ± 1.32 vs 0.31 ± 0.51 cm³, respectively; P =.002). Patients with severe pain showed a higher BMEL volume (1.2 ± 1.3 vs 0.2 ± 0.4 cm³, respectively; P =.046) and had a higher BM water fraction (26.0% ± 12.3% vs 8.6% ± 8.1%, respectively; P =.026) than did patients without pain. Conclusion: Qualitative and quantitative MRI parameters including the presence of subchondral defects, CRT2, BMEL volume, and BM water fraction were correlated with cartilage repair tissue quality and clinical symptoms. Therefore, the integrity of subchondral bone was associated with outcomes after osteochondral transplantation.