The MOBCART (magnetic resonance observation of bone and cartilage repair tissue) add-on score

Abstract Objectives To introduce the magnetic resonance observation of bone and cartilage repair tissue (MOBCART) bone score as a dedicated add-on to the established MOCART 2.0 knee score, and to evaluate its reproducibility for MRI-based assessment of the osseous component after osteochondral reconstruction of the knee. Materials and methods Thirty-two postoperative knee MRI examinations from 23 patients were scored using the three-domain MOBCART add-on (Integration, Normalization, Cysts; 0–50 points) by four independent readers (expert musculoskeletal radiologist, expert orthopedic cartilage specialist, radiology resident, orthopedic resident). Inter- and intrarater reliability were assessed using linear weighted kappa for individual ordinal domains and intraclass correlation coefficients (ICC; two-way mixed, absolute agreement, single measures) for the total score. Two readers repeated scoring for intrarater reliability. Results Interrater reliability across all four readers was moderate-to-good for the total score (ICC(A,1) = 0.72) and substantial-to-almost perfect for domain scores (κ = 0.71–0.82). Expert-reader agreement was good for the total score (ICC(A,1) = 0.90) and almost perfect for all domains (κ = 0.93–0.95). Intrarater reliability was excellent for Reader 1 (ICC(A,1) = 0.98) and good for Reader 4 (ICC(A,1) = 0.85). Conclusions The MOBCART add-on score is a reproducible, bone-focused supplement to the MOCART 2.0 knee score that enables standardized MRI reporting of osseous features after osteochondral reconstruction. Key Points Question Can a dedicated MRI add-on score to MOCART 2.0 reliably assess the osseous component after osteochondral knee repair across readers of varying experience? Findings The MOBCART add-on showed moderate-to-good interrater reliability across mixed-experience readers, good agreement between experts, and high test–retest reliability for both experienced and resident readers. Critical relevance statement As a complement to the MOCART 2.0 knee score, the MOBCART add-on score may facilitate standardized reporting of the osseous compartment after osteochondral reconstruction and enable objective comparison of bone-related imaging outcomes across procedures and studies.