Extrusion, meniscal signal change, loss of shape, synovitis and bone marrow oedema are reliable scoring parameters to assess MRI appearance post meniscal transplant

Purpose Meniscal allograft transplantation (MAT) has shown good promise in restoring normal knee joint biomechanics in a meniscal deficient patient. However, MRI appearance of the meniscal allograft is often questioned and raises concerns of its viability and function. This paper aims to introduce and validate a new scoring system for MAT MRI appearance at 12 months [MRI appearance in Meniscal Transplant Score (MIMS)], using key changes such as extrusion, meniscal signal change, loss of shape, synovitis and bone marrow oedema. Methods A retrospective analysis of 10 patients from a single surgeon series was conducted. All MAT were performed with soft tissue fixation technique. MRI was performed at 12 months post-transplant with two independent consultant musculoskeletal radiologists and one experienced meniscal transplant surgeon scoring the images obtained. Interobserver agreement and intraclass correlation were measured. Results Interobserver agreement between examiners on individual features of the MIMS was superior for tibial bone oedema, substantial for meniscal extrusion and femoral bone oedema, moderate for meniscal shape and synovitis, and fair for meniscal signal changes. Absolute agreement between raters found good reliability (ICC = 0.774; 95% 0.359, 0.960) for single measures and excellent reliability (ICC = 0.911; 95% 0.627, 0.986) for average measures. Conclusion MIMS is a reliable method of evaluating the meniscal allograft transplant 12 months post-transplant. Further research with larger MAT cohort groups and patient reported outcome measures may be helpful to correlate its clinical significance and guide further management. Level of evidence Level III.