Cartilage Repair Tissue Composition Assessed with 3-T MRI Correlates with Trabecular Bone Remodeling in Patients with Spongiosa-augmented Matrix-induced Autologous Chondrocyte Implantation

Introduction: To investigate whether maturation of cartilage repair tissue is associated with maturation of the subchondral bone in patients after spongiosa-augmented matrix-induced autologous chondrocyte implantation (MACI).

Materials and Methods: Both knees of 25 patients (25.5 ± 7.8 years of age; 10 female) were examined 2 years after unilateral spongiosa-augmented MACI at one femoral condyle using 3-T magnetic resonance imaging. Cartilage composition was assessed in all knee compartments using magnetic resonance imaging T2 relaxation time mapping. Three-dimensional phase-cycled balanced steady-state free-precision sequences were used to quantify the subchondral trabecular bone structure. Cartilage T2 values in the compartment treated with MACI (patella, medial, or lateral femur condyle) that were higher than those of the corresponding compartment of the contralateral knee were considered elevated. Values were compared using t tests.

Results: Cartilage T2 values were significantly higher in compartments undergoing cartilage repair compared with the corresponding compartment of the contralateral knee (mean ± standard error 41.1 ± 1.2 ms versus 38.8 ± 1.6 ms; p = 0.035). Apparent trabecular thickness and bone fraction were also significantly higher in the compartment undergoing cartilage repair compared with the contralateral side (each comparison, p < 0.001). The apparent trabecular thickness in the compartment undergoing cartilage repair was significantly higher in 17 patients with elevated cartilage T2 in the cartilage repair compartment (0.37 ± 0.05 mm) compared with 8 without elevated cartilage T2 (0.27 ± 0.05 mm; p = 0.042).

Conclusion: After spongiosa-augmented MACI, patients with elevated cartilage T2 values of the cartilage repair tissue showed thickened subchondral trabecular bone structure. The observed findings suggest a synergetic maturation of cartilage and subchondral bone after osteochondral transplantation.