Medial Scapular Body (MSB) Goutallier Classification - MRI based reliability and validity of evaluation of the Goutallier classification for grading fatty infiltration of the rotator cuff.

The degree of atrophy and fatty infiltration of rotator cuff muscle belly is a key predictor for cuff repairability. Traditionally, Goutallier grading of fatty infiltration is assessed at sagittal scapular Y-view. Massive rotator cuff tears are associated with tendon retraction and medial retraction of cuff musculature, resulting in medialization of the muscle bulk. Thus, standard Y-view can misrepresent the region of interest and may misguide clinicians when assessing repairability. It is hypothesized that by assessing the muscle belly with multiple medial sagittal MRI sections at medial scapular body, the Medial Scapular Body - Goutallier Classification (MSB-GC) will improve reliability and repeatability giving a more representative approximation to the degree of fatty infiltration, as compared with original Y-view. Fatty infiltration of the rotator cuff muscles were classified based on the Goutallier grade (0 to 4) at three defined sections section 1: original Y-view; section 2: level of suprascapular notch; section 3: three cm medial to suprascapular notch on MRI scans. Six sub-specialist fellowship trained shoulder surgeons, and three musculoskeletal radiologists independently evaluated deidentified MRI scans of included patients. Out of 80 scans, 78% (n=62) were massive cuff tears involving supraspinatus, infraspinatus and subscapularis tendon. Inter-observer reliability (consistency between observers) for Goutallier grade was excellent for all three predefined sections (range:0.87-0.95). Intra-observer reliability (repeatability) for Goutallier grade was excellent for all three sections and four rotator cuff muscles (range:0.83-0.97). There was a moderate to strong positive correlation of Goutallier grades between sections 1 and 3 and between sections 2 and 3 and these were statistically significant (p<0.001). There was a reduction in the severity of fatty infiltration on the Goutallier classification from sections 1 to 3 across all muscles. 42.5% of both supraspinatus and infraspinatus were downgraded by one, 20% of supraspinatus and 3.8% of infraspinatus were downgraded by 2 and 2.5% of supraspinatus were downgraded by 3. This study found that applying the Goutallier classification to more medial MRI sections (MSB-GC) resulted in assignment of lower grades for all rotator cuff muscles. Additionally, this method demonstrated excellent test-retest reliability and repeatability. Inclusion of a more medial view or whole scapula on MRI, especially in advanced levels of tear retraction, could be more reliable and representative for assessment of the degree of fatty infiltration within the muscle bulk that could help predict tear repairability and therefore improve clinical decision-making which should be studied further in clinical studies.

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