Objective: To investigate whether T2 relaxation time measurements of cartilage repair tissue and structural changes of the knee joint are associated with subchondral bone architecture after spongiosaaugmented matrix-associated autologous chondrocyte implantation (MACI). Design: Both knees of 25 patients (25.5 ± 7.8y; 10 women) were examined preoperatively and 2.7 years after unilateral spongiosa-augmented MACI with 3T magnetic resonance (MR) imaging. Cartilage composition was assessed using T2 relaxation time measurements, subchondral trabecular bone microstructure was quantified using a 3D phase-cycled balanced steady state free-precision sequence. Structural knee joint changes were assessed using the modified Whole-Organ Magnetic Resonance Imaging Score (WORMS). The Magnetic Resonance Observation of Cartilage Repair Tissue (MOCART) score was used for the postoperative description of the area that underwent MACI. Correlations were assessed using Spearman's rank correlation coefficients. Results: Hypertrophy of the cartilage repair tissue was found in 2 of 25 patients, both after a MACI procedure at the patella, 21 patients showed congruent filling. In subchondral bone of the cartilage repair compartment, apparent trabecular thickness was significantly higher in compartments with elevated cartilage T2 (n ¼ 17; 0.37 ± 0.05 mm) compared to those showing no difference in cartilage T2 compared to the same compartment in the contralateral knee (n ¼ 8; 0.27 ± 0.05 mm; P ¼ 0.042). Significant correlations were found between the overall progression of WORMS and the ipsilateral vs contralateral ratio of average trabecular thickness (r ¼ 0.48, P ¼ 0.031) and bone fraction (r ¼ 0.57, P ¼ 0.007). Conclusions: After spongiosa-augmented MACI, T2 values of cartilage repair tissue and structural knee joint changes correlated with the quality of the underlying trabecular bone.

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.

Background: Quantitative magnetic resonance (MR) imaging techniques are established for evaluation of cartilage composition and trabecular bone microstructure at the knee. It remains unclear whether quantitative MR parameters predict the midterm morphological outcome after matrix-associated chondrocyte implantation (MACI) with autologous bone grafting (ABG). Purpose: To assess longitudinal changes and associations of the biochemical composition of cartilage repair tissue, the subchondral bone architecture, and morphological knee joint abnormalities on 3-T MR imaging after MACI with ABG at the knee. Study Design: Case series; Level of evidence, 4. Methods: Knees of 18 patients (28.7 ± 8.4 years [mean ± SD]; 5 women) were examined preoperatively and 3, 6, 12, and 24 months after MACI and ABG using 3-T MR imaging. Cartilage composition was assessed using T2 relaxation time measurements. Subchondral bone microstructure was quantified using a 3-dimensional phase-cycled balanced steady-state free precision sequence. Trabecular bone parameters were calculated using a dual threshold algorithm (apparent bone fraction, apparent trabecular number, and apparent trabecular separation). Morphological abnormalities were assessed using the MOCART (magnetic resonace observation of cartilage repair tissue) score, the WORMS (Whole-Organ Magnetic Resonance Imaging Score), and the CROAKS (Cartilage Repair Osteoarthritis Knee Score). Clinical symptoms were assessed using the Tegner activity and Lysholm knee scores. Statistical analyses were performed by using multiple linear regression analysis. Results: Total WORMS ( P = .02) and MOCART ( P = .001) scores significantly improved over 24 months after MACI. Clinical symptoms were significantly associated with the presence of bone marrow edema pattern abnormalities 24 months after surgery ( P = .035). Overall there was a good to excellent radiological outcome found after 24 months (MOCART score, 88.8 ± 10.1). Cartilage repair T2 values significantly decreased between 12 and 24 months after MACI ( P = .009). Lower global T2 values after 3 months were significantly associated with better MOCART scores after 24 months ( P = .04). Moreover, trabecular bone parameters after 3 months were significantly associated with the total WORMS after 24 months (apparent bone fraction, P = .048; apparent trabecular number, P = .013; apparent trabecular separation, P = .013). Conclusion: After MACI with ABG, early postoperative quantitative assessment of biochemical composition of cartilage and microstructure of subchondral bone may predict the outcome after 24 months. The perioperative global joint cartilage matrix quality is essential for proper proliferation of the repair tissue, reflected by MOCART scores. The subchondral bone quality of the ABG site is essential for proper maturation of the cartilage repair tissue, reflected by cartilage T2 values.