Introduction

Since the first introduction of the MOCART score, cartilage repair techniques and MR imaging have undergone significant change. Novel, scaffold-based surgical treatment options render the assessment of subchondral bone more important. At the same time, other aspects, such as the assessment of adhesions, which were formerly frequent complications with periosteal flaps, became less relevant due to the introduction of second-generation ACI. Furthermore, the continuous development of new MR sequences and improved MR hardware - in particular, MR scanners that operate at high field-strengths (3 Tesla) and better coil configuration (phased array designs) have improved routine clinical MR examinations and MR protocols over the last decade. These developments will be addressed with this update to the MOCART score.

Furthermore, we recognized that the linguistically defined categories of the original MOCART score may be interpreted in different ways by different readers, thus introducing variability and decreasing interrater reliability.

Hence, the aim of this study was to develop an incremental update to the original MOCART score for the assessment of cartilage repair of the knee joint, which would account for the above-mentioned advancements and address issues identified in the clinical routine. Intra- and inter-rater reliability should be evaluated by expert readers.

Content

Materials and Methods: The degree of defect filling is now assessed in 25% increments, with hypertrophic filling of up to 150% receiving the same scoring as complete repair. Integration now assesses only the integration to neighboring cartilage, and the severity of surface damage is assessed in reference to cartilage repair length rather than depth. The signal intensity of the repair tissue is scored as minor abnormal or severely abnormal on a proton density-weighted TSE sequence only and differentiates between hyperintene and hypointense signal alterations. The assessment of the variables “subchondral lamina”, “adhesions” and “synovitis” was removed and the points were reallocated to the newly introduced variable “bony defect or bony overgrowth”. The variable “subchondral bone” was renamed to “subchondral changes” and assesses minor and severe edema-like marrow signal, as well as subchondral cysts or osteonecrosis-like signal. Overall, a MOCART score ranging from 0 to 100 points may be reached. Four independent readers (two expert readers and two radiology residents with limited experience) assessed the 3 Tesla MRI examinations of 24 patients, who had undergone cartilage repair of a femoral cartilage defect using the new MOCART 2.0 knee score. One of the expert readers and both inexperienced readers performed two readings, separated by a four-week interval. For the inexperienced readers, the first reading was based on the evaluation sheet only. For the second reading, a newly introduced atlas was used as an additional reference. Interrater reliability was assessed using intraclass correlation coefficients (ICCs). ICCs were interpreted according to the criteria of Landis and Koch.

Results: The overall intra-rater (ICC = 0.88, p < 0.001) as well as the inter-rater (ICC = 0.84, p < 0.001) reliability of the expert readers was almost perfect. Based on the evaluation sheet of the MOCART 2.0 knee score, the overall inter-rater reliability of the inexperienced readers compared to expert reader 1 was moderate (ICC = 0.45, p < 0.01), ranging from poor (structure: ICC=0.15, p = 0.09) to substantial (“bony defect or overgrowth”: ICC = 0.65, p < 0.001) for different variables. With the additional use of the atlas, the overall inter-rater reliability of the inexperienced readers was substantial (ICC = 0.63, p < 0.001), ranging from moderate (signal: ICC = 0.42, p < 0.01) to substantial (integration ICC = 0.73, p < 0.001).

Conclusions: The MOCART 2.0 knee score was updated to account for important changes in the past decade and demonstrates almost-perfect inter- and intra-rater reliability in expert readers. In inexperienced readers use of the atlas may improve inter-rater reliability, and thus, increase the comparability of results across studies.

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