Inter-rater reliability between two examiners with different professional roles in the evaluation of fat infiltration in the lumbar paraspinal muscles using magnetic resonance imaging.

[Purpose] To clarify the inter-rater reliability of the evaluation criteria for paraspinal muscle fat infiltration on magnetic resonance images between two examiners with different professional roles in interdisciplinary physical therapy teams. [Participants and Methods] In this retrospective study, we reviewed the clinical data of 225 patients with degenerative lumbar diseases who underwent posterior lumbar surgery at our hospital. A physical therapist and a spinal surgeon visually quantified fat infiltration of the multifidus muscles at the level of L4/5 on the preoperative magnetic resonance images of the patients using Kjaer's criteria (Grade 0: 0-10%, Grade 1: 10-50%, and Grade 2: >50%). We used the kappa coefficient to assess inter-rater reliability. [Results] The participants included 142 males and 83 females (mean age, 64.7 years; range, 21-89 years). The number of patients with grades 0/1/2 were 50/160/15, respectively, for examiner 1; and 59/155/11, respectively, for examiner 2. The kappa coefficient was 0.69, indicating a substantial agreement. [Conclusion] Our study, which is the first to assess the inter-rater reliability of Kjaer's criteria between examiners with different medical occupations, revealed that these criteria could be a reliable tool for evaluating fat infiltration in the multifidus muscles and sharing information between interdisciplinary physical therapy teams.